WorldWideScience

Sample records for heterostructure unipolar spin

  1. Thermoelectric unipolar spin battery in a suspended carbon nanotube

    Science.gov (United States)

    Cao, Zhan; Fang, Tie-Feng; He, Wan-Xiu; Luo, Hong-Gang

    2017-04-01

    A quantum dot formed in a suspended carbon nanotube exposed to an external magnetic field is predicted to act as a thermoelectric unipolar spin battery which generates pure spin current. The built-in spin flip mechanism is a consequence of the spin-vibration interaction resulting from the interplay between the intrinsic spin-orbit coupling and the vibrational modes of the suspended carbon nanotube. On the other hand, utilizing thermoelectric effect, the temperature difference between the electron and the thermal bath to which the vibrational modes are coupled provides the driving force. We find that both magnitude and direction of the generated pure spin current are dependent on the strength of spin-vibration interaction, the sublevel configuration in dot, the temperatures of electron and thermal bath, and the tunneling rate between the dot and the pole. Moreover, in the linear response regime, the kinetic coefficient is non-monotonic in the temperature T and it reaches its maximum when {{k}\\text{B}}T is about one phonon energy. The existence of a strong intradot Coulomb interaction is irrelevant for our spin battery, provided that high-order cotunneling processes are suppressed.

  2. Thermoelectric unipolar spin battery in a suspended carbon nanotube.

    Science.gov (United States)

    Cao, Zhan; Fang, Tie-Feng; He, Wan-Xiu; Luo, Hong-Gang

    2017-04-26

    A quantum dot formed in a suspended carbon nanotube exposed to an external magnetic field is predicted to act as a thermoelectric unipolar spin battery which generates pure spin current. The built-in spin flip mechanism is a consequence of the spin-vibration interaction resulting from the interplay between the intrinsic spin-orbit coupling and the vibrational modes of the suspended carbon nanotube. On the other hand, utilizing thermoelectric effect, the temperature difference between the electron and the thermal bath to which the vibrational modes are coupled provides the driving force. We find that both magnitude and direction of the generated pure spin current are dependent on the strength of spin-vibration interaction, the sublevel configuration in dot, the temperatures of electron and thermal bath, and the tunneling rate between the dot and the pole. Moreover, in the linear response regime, the kinetic coefficient is non-monotonic in the temperature T and it reaches its maximum when [Formula: see text] is about one phonon energy. The existence of a strong intradot Coulomb interaction is irrelevant for our spin battery, provided that high-order cotunneling processes are suppressed.

  3. Topological superconductivity in metal/quantum-spin-ice heterostructures

    Science.gov (United States)

    She, Jian-Huang; Kim, Choong H.; Fennie, Craig J.; Lawler, Michael J.; Kim, Eun-Ah

    2017-11-01

    We propose a strategy to achieve an unconventional superconductor in a heterostructure: use a quantum paramagnet (QPM) as a substrate for heterostructure growth of metallic films to design exotic superconductors. The proposed setup allows us to "customize" electron-electron interaction imprinted on the metallic layer. The QPM material of our choice is quantum spin ice. Assuming the metallic layer forms a single isotropic Fermi pocket, we predict its coupling to spin fluctuations in quantum spin ice will drive topological odd-parity pairing. We further present guiding principles for materializing the suitable heterostructure using ab initio calculations and describe the band structure we predict for the case of Y2Sn2-xSbxO7 grown on the (111) surface of Pr2Zr2O7. Using this microscopic information, we predict topological odd-parity superconductivity at a few Kelvin in this heterostructure, which is comparable to the Tc of the only other confirmed odd-parity superconductor Sr2RuO4.

  4. Spin-torque generation in topological insulator based heterostructures

    KAUST Repository

    Fischer, Mark H.

    2016-03-11

    Heterostructures utilizing topological insulators exhibit a remarkable spin-torque efficiency. However, the exact origin of the strong torque, in particular whether it stems from the spin-momentum locking of the topological surface states or rather from spin-Hall physics of the topological-insulator bulk, remains unclear. Here, we explore a mechanism of spin-torque generation purely based on the topological surface states. We consider topological-insulator-based bilayers involving ferromagnetic metal (TI/FM) and magnetically doped topological insulators (TI/mdTI), respectively. By ascribing the key theoretical differences between the two setups to location and number of active surface states, we describe both setups within the same framework of spin diffusion of the nonequilibrium spin density of the topological surface states. For the TI/FM bilayer, we find large spin-torque efficiencies of roughly equal magnitude for both in-plane and out-of-plane spin torques. For the TI/mdTI bilayer, we elucidate the dominance of the spin-transfer-like torque. However, we cannot explain the orders of magnitude enhancement reported. Nevertheless, our model gives an intuitive picture of spin-torque generation in topological-insulator-based bilayers and provides theoretical constraints on spin-torque generation due to topological surface states.

  5. Spin-polarized photoemission from SiGe heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Ferrari, A.; Bottegoni, F.; Isella, G.; Cecchi, S.; Chrastina, D.; Finazzi, M.; Ciccacci, F. [LNESS-Dipartimento di Fisica, Politecnico di Milano, Piazza Leonardo da Vinci 32, 20133 Milano (Italy)

    2013-12-04

    We apply the principles of Optical Orientation to measure by Mott polarimetry the spin polarization of electrons photoemitted from different group-IV heterostructures. The maximum measured spin polarization, obtained from a Ge/Si{sub 0.31}Ge{sub 0.69} strained film, undoubtedly exceeds the maximum value of 50% attainable in bulk structures. The explanation we give for this result lies in the enhanced band orbital mixing between light hole and split-off valence bands as a consequence of the compressive strain experienced by the thin Ge layer.

  6. Unipolar and bipolar operation of InAs/InSb nanowire heterostructure field-effect transistors

    Science.gov (United States)

    Nilsson, Henrik A.; Caroff, Philippe; Lind, Erik; Pistol, Mats-Erik; Thelander, Claes; Wernersson, Lars-Erik

    2011-09-01

    We present temperature dependent electrical measurements on n-type InAs/InSb nanowire heterostructure field-effect transistors. The barrier height of the heterostructure junction is determined to be 220 meV, indicating a broken bandgap alignment. A clear asymmetry is observed when applying a bias to either the InAs or the InSb side of the junction. Impact ionization and band-to-band tunneling is more pronounced when the large voltage drop occurs in the narrow bandgap InSb segment. For small negative gate-voltages, the InSb segment can be tuned toward p-type conduction, which induces a strong band-to-band tunneling across the heterostructucture junction.

  7. Spin-orbit-coupled transport and spin torque in a ferromagnetic heterostructure

    KAUST Repository

    Wang, Xuhui

    2014-02-07

    Ferromagnetic heterostructures provide an ideal platform to explore the nature of spin-orbit torques arising from the interplay mediated by itinerant electrons between a Rashba-type spin-orbit coupling and a ferromagnetic exchange interaction. For such a prototypic system, we develop a set of coupled diffusion equations to describe the diffusive spin dynamics and spin-orbit torques. We characterize the spin torque and its two prominent—out-of-plane and in-plane—components for a wide range of relative strength between the Rashba coupling and ferromagnetic exchange. The symmetry and angular dependence of the spin torque emerging from our simple Rashba model is in an agreement with experiments. The spin diffusion equation can be generalized to incorporate dynamic effects such as spin pumping and magnetic damping.

  8. Giant thermopower in superconducting heterostructures with spin-active interfaces

    Energy Technology Data Exchange (ETDEWEB)

    Kalenkov, Mikhail S. [I.E. Tamm Department of Theoretical Physics, P.N. Lebedev Physical Institute, 119991 Moscow (Russian Federation); Laboratory of Cryogenic Nanoelectronics, Nizhny Novgorod State Technical University, 603950 Nizhny Novgorod (Russian Federation); Zaikin, Andrei D. [Institut für Nanotechnologie, Karlsruher Institut für Technologie (KIT), 76021 Karlsruhe (Germany); I.E. Tamm Department of Theoretical Physics, P.N. Lebedev Physical Institute, 119991 Moscow (Russian Federation)

    2015-06-01

    We predict parametrically strong enhancement of the thermoelectric effect in metallic bilayers consisting of two superconductors separated by a spin-active interface. The physical mechanism for such an enhancement is directly related to electron–hole imbalance generated by spin-sensitive quasiparticle scattering at the interface between superconducting layers. We explicitly evaluate the thermoelectric currents flowing in the system and demonstrate that they can reach maximum values comparable to the critical ones for superconductors under consideration. - Highlights: • Strong enhancement of the thermoelectric effect in superconducting heterostructures. • Generation of the electron-hole imbalance by spin-sensitive quasiparticle scattering. • Thermoelectric currents can reach maximum values comparable to the critical ones.

  9. Spin-Dependent Transport Phenomena in Ferromagnet/Semiconductor Heterostructures

    Science.gov (United States)

    Geppert, Chad Christopher

    This dissertation examines several aspects of spin-dependent transport phenomena in epitaxially grown ferromagnet/n-GaAs heterostructures. Further maturation of the field of semiconductor-based spintronics is hindered by difficulties in evaluating device performance across materials systems. Using Fe/n-GaAs and Co2MnSi/n-GaAs heterostructures as a test case, the main goal of this work is to demonstrate how such difficulties may be overcome by (1) specifying a more quantitative framework for evaluating transport parameters and (2) the introduction of a new spin-to-charge conversion phenomenon which may be parameterized by bulk semiconductor parameters. In the introductory chapter, this work is placed in the broader context of developing improved methods for the generation, modulation, and detection of spins. The lateral spin-valve geometry is presented as a concrete example of the typical measurement procedures employed. Chapter 2 presents the charge-based transport properties of these samples and establishes the notation and calculation techniques to be employed in subsequent chapters. In particular, we examine in detail the calculation of the electrochemical potential for a given carrier concentration. Chapter 3 provides a full derivation of the equations governing spin-dependent transport in the large polarization regime. This is applied to the case of extracting spin lifetimes and diffusion rates, demonstrating how quantitative agreement with theoretical predictions may be obtained upon properly accounting for both device geometry and material parameters. Further examination of the boundary conditions applicable to the heterojunctions of these samples demonstrates to what extent device performance may be parameterized across materials systems. Chapter 4 presents experimental observations of a new spin-to-charge conversion phenomenon using a non-magnetic probe. In the presence of a large non-equilibrium spin accumulation, the combination of a non-constant density

  10. Spin accumulation in permalloy-ZnO heterostructures from both electrical injection and spin pumping

    Science.gov (United States)

    Wang, Xiaowei; Yang, Yumeng; Wang, Ying; Luo, Ziyan; Xie, Hang; Wu, Yihong

    2017-11-01

    We report the results of room temperature spin injection and detection studies in ZnO using both electrical injection and spin pumping. At ferromagnetic resonance, an interfacial voltage with a constant polarity upon magnetization reversal is observed in permalloy-ZnO heterostructures, which is attributed to spin accumulation after ruling out other origins. Simultaneous electrical injection during spin pumping is achieved in samples with large interface resistance or insertion of a thin MgO layer at the interface of permalloy and ZnO. From the pumping frequency dependence of detected voltage, a spin lifetime of 32 ps is extracted for ZnO at room temperature, despite the fact that there was no Hanle effect observed in the same device using the conventional three-terminal DC measurement.

  11. Gate-Tunable Spin Transport and Giant Electroresistance in Ferromagnetic Graphene Vertical Heterostructures

    Science.gov (United States)

    Myoung, Nojoon; Park, Hee Chul; Lee, Seung Joo

    2016-04-01

    Controlling tunneling properties through graphene vertical heterostructures provides advantages in achieving large conductance modulation which has been known as limitation in lateral graphene device structures. Despite of intensive research on graphene vertical heterosturctures for recent years, the potential of spintronics based on graphene vertical heterostructures remains relatively unexplored. Here, we present an analytical device model for graphene-based spintronics by using ferromagnetic graphene in vertical heterostructures. We consider a normal or ferroelectric insulator as a tunneling layer. The device concept yields a way of controlling spin transport through the vertical heterostructures, resulting in gate-tunable spin-switching phenomena. Also, we revealed that a ‘giant’ resistance emerges through a ferroelectric insulating layer owing to the anti-parallel configuration of ferromagnetic graphene layers by means of electric fields via gate and bias voltages. Our findings discover the prospect of manipulating the spin transport properties in vertical heterostructures without use of magnetic fields.

  12. Physics and application of persistent spin helix state in semiconductor heterostructures

    Science.gov (United States)

    Kohda, Makoto; Salis, Gian

    2017-07-01

    In order to utilize the spin degree of freedom in semiconductors, control of spin states and transfer of the spin information are fundamental requirements for future spintronic devices and quantum computing. Spin orbit (SO) interaction generates an effective magnetic field for moving electrons and enables spin generation, spin manipulation and spin detection without using external magnetic field and magnetic materials. However, spin relaxation also takes place due to a momentum dependent SO-induced effective magnetic field. As a result, SO interaction is considered to be a double-edged sword facilitating spin control but preventing spin transport over long distances. The persistent spin helix (PSH) state solves this problem since uniaxial alignment of the SO field with SU(2) symmetry enables the suppression of spin relaxation while spin precession can still be controlled. Consequently, understanding the PSH becomes an important step towards future spintronic technologies for classical and quantum applications. Here, we review recent progress of PSH in semiconductor heterostructures and its device application. Fundamental physics of SO interaction and the conditions of a PSH state in semiconductor heterostructures are discussed. We introduce experimental techniques to observe a PSH and explain both optical and electrical measurements for detecting a long spin relaxation time and the formation of a helical spin texture. After emphasizing the bulk Dresselhaus SO coefficient γ, the application of PSH states for spin transistors and logic circuits are discussed.

  13. Green's function formalism for spin transport in metal-insulator-metal heterostructures

    Science.gov (United States)

    Zheng, Jiansen; Bender, Scott; Armaitis, Jogundas; Troncoso, Roberto E.; Duine, Rembert A.

    2017-11-01

    We develop a Green's function formalism for spin transport through heterostructures that contain metallic leads and insulating ferromagnets. While this formalism in principle allows for the inclusion of various magnonic interactions, we focus on Gilbert damping. As an application, we consider ballistic spin transport by exchange magnons in a metal-insulator-metal heterostructure with and without disorder. For the former case, we show that the interplay between disorder and Gilbert damping leads to spin current fluctuations. For the case without disorder, we obtain the dependence of the transmitted spin current on the thickness of the ferromagnet. Moreover, we show that the results of the Green's function formalism agree in the clean and continuum limit with those obtained from the linearized stochastic Landau-Lifshitz-Gilbert equation. The developed Green's function formalism is a natural starting point for numerical studies of magnon transport in heterostructures that contain normal metals and magnetic insulators.

  14. Gate-Controlled Electron Spin Resonance in a GaAs/AlGaAs Heterostructure

    OpenAIRE

    Jiang, H. W.; Yablonovitch, E.

    2001-01-01

    The electron spin resonance (ESR) of two-dimensional electrons is investigated in a gated GaAs/AlGaAs heterostructure. We found that the ESR resonance frequency can be turned by means of a gate voltage. The front and back gates of the heterostructure produce opposite g-factor shift, suggesting that electron g-factor is being electrostatically controlled by shifting the equilibrium position of the electron wave function from one epitaxial layer to another with different g-factors.

  15. Inversion of Spin Signal and Spin Filtering in Ferromagnet|Hexagonal Boron Nitride-Graphene van der Waals Heterostructures

    Science.gov (United States)

    Kamalakar, M. Venkata; Dankert, André; Kelly, Paul J.; Dash, Saroj P.

    2016-01-01

    Two dimensional atomically thin crystals of graphene and its insulating isomorph hexagonal boron nitride (h-BN) are promising materials for spintronic applications. While graphene is an ideal medium for long distance spin transport, h-BN is an insulating tunnel barrier that has potential for efficient spin polarized tunneling from ferromagnets. Here, we demonstrate the spin filtering effect in cobalt|few layer h-BN|graphene junctions leading to a large negative spin polarization in graphene at room temperature. Through nonlocal pure spin transport and Hanle precession measurements performed on devices with different interface barrier conditions, we associate the negative spin polarization with high resistance few layer h-BN|ferromagnet contacts. Detailed bias and gate dependent measurements reinforce the robustness of the effect in our devices. These spintronic effects in two-dimensional van der Waals heterostructures hold promise for future spin based logic and memory applications. PMID:26883717

  16. Effect of rare earth metal on the spin-orbit torque in magnetic heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Ueda, Kohei; Pai, Chi-Feng; Tan, Aik Jun; Mann, Maxwell; Beach, Geoffrey S. D., E-mail: gbeach@mit.edu [Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States)

    2016-06-06

    We report the effect of the rare earth metal Gd on current-induced spin-orbit torques (SOTs) in perpendicularly magnetized Pt/Co/Gd heterostructures, characterized using harmonic measurements and spin-torque ferromagnetic resonance (ST-FMR). By varying the Gd metal layer thickness from 0 nm to 8 nm, harmonic measurements reveal a significant enhancement of the effective fields generated from the Slonczewski-like and field-like torques. ST-FMR measurements confirm an enhanced effective spin Hall angle and show a corresponding increase in the magnetic damping constant with increasing Gd thickness. These results suggest that Gd plays an active role in generating SOTs in these heterostructures. Our finding may lead to spin-orbitronics device application such as non-volatile magnetic random access memory, based on rare earth metals.

  17. Tunable Short-Wavelength Spin-Wave Emission and Confinement in Anisotropy-Modulated Multiferroic Heterostructures

    Science.gov (United States)

    Hämäläinen, Sampo J.; Brandl, Florian; Franke, Kévin J. A.; Grundler, Dirk; van Dijken, Sebastiaan

    2017-07-01

    We report on the generation and confinement of short-wavelength spin waves in a continuous film with periodically modulated magnetic anisotropy. The concept, which is demonstrated for strain-coupled Co40Fe40B20/BaTiO3 heterostructures, relies on abrupt rotation of magnetic anisotropy at the boundaries of magnetic stripe domains. In combination with an external bias field, this modulation of magnetic anisotropy produces a lateral variation of the effective magnetic field, leading to local spin-wave excitation when irradiated by a microwave magnetic field. In domains with small effective field, spin waves are perfectly confined by the spin gap in neighboring domains. In contrast, standing spin waves in domains with large effective field radiate into neighboring domains. Using micromagnetic simulation, we show that the wavelength of emitted spin waves is tunable from a few micrometers down to about 100 nm by rotation of the bias field. Importantly, the orientation of the wave front remains fixed. We also demonstrate that dynamic fluctuations of the effective magnetic field produce exchange-dominated spin waves at single-anisotropy boundaries. The multiferroic heterostructures presented here enable the use of global excitation fields from a microwave antenna to emit tunable spin waves from a nanometer-wide line source at well-defined locations of a continuous ferromagnetic film.

  18. Large spin-orbit torques in Pt/Co-Ni/W heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Yu, Jiawei; Qiu, Xuepeng; Legrand, William; Yang, Hyunsoo, E-mail: eleyang@nus.edu.sg [Department of Electrical and Computer Engineering, National University of Singapore, Singapore 117576 (Singapore)

    2016-07-25

    The spin orbit torques (SOTs) in perpendicularly magnetized Co-Ni multilayers sandwiched between two heavy metals (HM) have been studied. By exploring various HM materials, we show an efficient enhancement or cancellation of the total SOT, depending on the combination of the two HM materials. The maximum SOT effective field is obtained in Pt/Co-Ni/W heterostructures. We also model our double HM system and show that the effective spin Hall angle has a peak value at certain HM thicknesses. Measuring the SOT in Pt/Co-Ni/W for various W thicknesses confirms an effective spin Hall angle up to 0.45 in our double HM system.

  19. Angular dependence and symmetry of Rashba spin torque in ferromagnetic heterostructures

    KAUST Repository

    Ortiz Pauyac, Christian

    2013-06-26

    In a ferromagnetic heterostructure, the interplay between Rashba spin-orbit coupling and exchange splitting gives rise to a current-driven spin torque. In a realistic device setup, we investigate the Rashba spin torque in the diffusive regime and report two major findings: (i) a nonvanishing torque exists at the edges of the device even when the magnetization and effective Rashba field are aligned; (ii) anisotropic spin relaxation rates driven by the Rashba spin-orbit coupling assign the spin torque a general expression T = T y (θ) m × (y × m) + T y (θ) y × m + T z (θ) m × (z × m) + T z (θ) z × m, where the coefficients T, y, z depend on the magnetization direction. Our results agree with recent experiments. © 2013 AIP Publishing LLC.

  20. Spin-Orbit Torque from a Magnetic Heterostructure of High-Entropy Alloy

    Science.gov (United States)

    Chen, Tian-Yue; Chuang, Tsao-Chi; Huang, Ssu-Yen; Yen, Hung-Wei; Pai, Chi-Feng

    2017-10-01

    High-entropy alloy (HEA) is a family of metallic materials with nearly equal partitions of five or more metals, which might possess mechanical and transport properties that are different from conventional binary or tertiary alloys. In this work, we demonstrate current-induced spin-orbit torque (SOT) magnetization switching in a Ta-Nb-Hf-Zr-Ti HEA-based magnetic heterostructure with perpendicular magnetic anisotropy. The maximum dampinglike SOT efficiency from this particular HEA-based magnetic heterostructure is further determined to be |ζDLHEA | ≈0.033 by hysteresis-loop-shift measurements, while that for the Ta control sample is |ζDLTa | ≈0.04 . Our results indicate that HEA-based magnetic heterostructures can serve as an alternative group of potential candidates for SOT device applications due to the possibility of tuning buffer-layer properties with more than two constituent elements.

  1. Van der Waals engineering of ferromagnetic semiconductor heterostructures for spin and valleytronics

    Science.gov (United States)

    Zhong, Ding; Seyler, Kyle L.; Linpeng, Xiayu; Cheng, Ran; Sivadas, Nikhil; Huang, Bevin; Schmidgall, Emma; Taniguchi, Takashi; Watanabe, Kenji; McGuire, Michael A.; Yao, Wang; Xiao, Di; Fu, Kai-Mei C.; Xu, Xiaodong

    2017-01-01

    The integration of magnetic material with semiconductors has been fertile ground for fundamental science as well as of great practical interest toward the seamless integration of information processing and storage. We create van der Waals heterostructures formed by an ultrathin ferromagnetic semiconductor CrI3 and a monolayer of WSe2. We observe unprecedented control of the spin and valley pseudospin in WSe2, where we detect a large magnetic exchange field of nearly 13 T and rapid switching of the WSe2 valley splitting and polarization via flipping of the CrI3 magnetization. The WSe2 photoluminescence intensity strongly depends on the relative alignment between photoexcited spins in WSe2 and the CrI3 magnetization, because of ultrafast spin-dependent charge hopping across the heterostructure interface. The photoluminescence detection of valley pseudospin provides a simple and sensitive method to probe the intriguing domain dynamics in the ultrathin magnet, as well as the rich spin interactions within the heterostructure. PMID:28580423

  2. Interface symmetry and spin control in topological-insulator-semiconductor heterostructures

    Science.gov (United States)

    Asmar, Mahmoud M.; Sheehy, Daniel E.; Vekhter, Ilya

    2017-06-01

    Heterostructures combining topological and nontopological materials constitute the next frontier in the effort to incorporate topological insulators (TIs) into electronic devices. We show that the properties of the interface states appearing at the boundary between a topologically trivial semiconductor (SE) and a TI are controlled by the lowering of the interface symmetry due to the presence of the SE. For the [111]-grown heterostructure, SE-TI interface states exhibit elliptical contours of constant energy and complex spin textures with broken helicity, in contrast to the well-studied helical Dirac surface states. We derive a general effective Hamiltonian for SE-TI junctions, and propose experimental signatures such as an out of plane spin accumulation under a transport current and the opening of a spectral gap that depends on the direction of an applied in-plane magnetic field.

  3. Tunable Rashba spin splitting in two-dimensional graphene/As-I heterostructures

    Science.gov (United States)

    Yu, Niannian; Yuan, Junhui; Li, Kaixuan; Wang, Jiafu

    2018-01-01

    Interlayer distance induced Rashba spin splitting is predicted in graphene and monolayer iodinated arsenene (As-I) van der Waals heterostructures based on first-principle calculations. The equilibrium structure of graphene/As-I exhibits a linear Dirac-like dispersion relation at K point in Brillouin zone. With the change of interlayer distance, large and tunable Rashba spin splitting can be realized from zero to more than 100 meV. Projected band structure analysis is performed, which indicates a strong relation between the extent of band splitting and the hybridization of C and As orbitals near the Fermi level. Meanwhile, charge density difference calculations reveal a pronounce charge transfer between graphene and As-I with varying interlayer distances, leading to the change of built-in electric filed along z direction that modifies the electronic structures significantly. Our work may make a special contribution to the realization and application of spintronic devices based on van der Waals heterostructures.

  4. Hole spin coherence in a Ge/Si heterostructure nanowire.

    Science.gov (United States)

    Higginbotham, A P; Larsen, T W; Yao, J; Yan, H; Lieber, C M; Marcus, C M; Kuemmeth, F

    2014-06-11

    Relaxation and dephasing of hole spins are measured in a gate-defined Ge/Si nanowire double quantum dot using a fast pulsed-gate method and dispersive readout. An inhomogeneous dephasing time T2* 0.18 μs exceeds corresponding measurements in III–V semiconductors by more than an order of magnitude, as expected for predominately nuclear-spin-free materials. Dephasing is observed to be exponential in time, indicating the presence of a broadband noise source, rather than Gaussian, previously seen in systems with nuclear-spin-dominated dephasing.

  5. Spin-polarized ballistic conduction through correlated Au-NiMnSb-Au heterostructures

    Science.gov (United States)

    Morari, C.; Appelt, W. H.; Östlin, A.; Prinz-Zwick, A.; Schwingenschlögl, U.; Eckern, U.; Chioncel, L.

    2017-11-01

    We examine the ballistic conduction through Au-NiMnSb-Au heterostructures consisting of up to four units of the half-metallic NiMnSb in the scattering region, using density functional theory (DFT) methods. For a single NiMnSb unit the transmission function displays a spin polarization of around 50 % in a window of 1 eV centered around the Fermi level. By increasing the number of layers, an almost complete spin polarization of the transmission is obtained in this energy range. Supplementing the DFT calculations with local electronic interactions, of Hubbard-type on the Mn sites, leads to a hybridization between the interface and many-body states. The significant reduction of the spin polarization seen in the density of states is not apparent in the spin polarization of the conduction electron transmission, which suggests that the hybridized interface and many-body induced states are localized.

  6. Spin-polarized ballistic conduction through correlated Au-NiMnSb-Au heterostructures

    KAUST Repository

    Morari, C.

    2017-11-20

    We examine the ballistic conduction through Au-NiMnSb-Au heterostructures consisting of up to four units of the half-metallic NiMnSb in the scattering region, using density functional theory (DFT) methods. For a single NiMnSb unit the transmission function displays a spin polarization of around 50% in a window of 1eV centered around the Fermi level. By increasing the number of layers, an almost complete spin polarization of the transmission is obtained in this energy range. Supplementing the DFT calculations with local electronic interactions, of Hubbard-type on the Mn sites, leads to a hybridization between the interface and many-body states. The significant reduction of the spin polarization seen in the density of states is not apparent in the spin polarization of the conduction electron transmission, which suggests that the hybridized interface and many-body induced states are localized.

  7. Kane model for the spin-splitting of holes in semiconductor heterostructures

    Science.gov (United States)

    Wong, Arturo; Mireles, Francisco

    2006-03-01

    We present a theoretical study of the Rashba-like spin-orbit coupling in two dimensional hole systems formed in zincblende semiconductor heterostructures. Using an 8X8 band Kane model within the envelope function approximation we derive exact analytical expressions for the Rashba-like Hamiltonians of the heavy, light and split-off holes [1]. The linear and cubic dependence in the wave vector of such Hamiltonians will be discussed. Simple analytical expressions for the spin-orbit coupling parameters can be also extracted from our model. A variational approach has been used in order to estimate the hole spin-splitting energies in typical III-V semiconductor quantum wells. Our preliminary results indicate that the magnitude of the spin-splitting energies for heavy holes is generically larger than their counterparts for electrons. This results could be of relevance for the design and implementation of novel (hole) transport spintronic devices. [1] A. Wong and F. Mireles (in preparation)

  8. Hole Spin Coherence in a Ge/Si Heterostructure Nanowire

    OpenAIRE

    Higginbotham, A. P.; Larsen, T. W.; Yao, J.; Yan, H.; Lieber, C. M.; Marcus, C. M.; Kuemmeth, F.

    2014-01-01

    Relaxation and dephasing of hole spins are measured in a gate-defined Ge/Si nanowire double quantum dot using a fast pulsed-gate method and dispersive readout. An inhomogeneous dephasing time $T_2^* \\sim 0.18~\\mathrm{\\mu s}$ exceeds corresponding measurements in III-V semiconductors by more than an order of magnitude, as expected for predominately nuclear-spin-free materials. Dephasing is observed to be exponential in time, indicating the presence of a broadband noise source, rather than Gaus...

  9. Spin manipulation at the interface of a topological insulator/GaAs heterostructure

    Science.gov (United States)

    Qu, Dongxia; Che, Xiaoyu; Kou, Xufeng; Lang, Murong; Crowhurst, Jonathan; Armstrong, Michael R.; Zaug, Joseph; Wang, Kang L.; Chapline, George F.; Lawrence Livermore National Laboratory Team; University of California, Los Angeles Team

    One primary goal of spintronics is to discover materials and devices, which enable efficient electrical control of spins. The emerging field of topological insulator (TI) provides intriguing opportunities for spin generation and manipulation, owing to its strong spin-orbit character. Here we report that spins can be driven from a topological insulator thin film (Bi0.5Sb0.5)2 Te3 into an adjacent semiconductor GaAs at room temperature. In a TI/GaAs heterostructure, a photo-induced spin current flows across the interface and induces an electrical current via the inverse spin Hall effect, which converts the spin current into a charge current. We find that the magnitude and direction of the helicity-dependent photocurrent can be controlled by gate-voltage, indicative of electric tuning of the spin configuration. This work is supported by Grants 15-LW-018 and 16-SI-004 from the Department of Energy, Laboratory Directed Research and Development (LDRD) funding.

  10. Hole spin coherence in a Ge/Si heterostructure nanowire

    DEFF Research Database (Denmark)

    Higginbotham, Andrew P; Larsen, Thorvald Wadum; Yao, Jun

    2014-01-01

    Relaxation and dephasing of hole spins are measured in a gate-defined Ge/Si nanowire double quantum dot using a fast pulsed-gate method and dispersive readout. An inhomogeneous dephasing time T2(*)≈ 0.18 μs exceeds corresponding measurements in III-V semiconductors by more than an order of magnit......Relaxation and dephasing of hole spins are measured in a gate-defined Ge/Si nanowire double quantum dot using a fast pulsed-gate method and dispersive readout. An inhomogeneous dephasing time T2(*)≈ 0.18 μs exceeds corresponding measurements in III-V semiconductors by more than an order...

  11. Gate-controlled electron spin resonance in GaAs/AlxGa1-xAs heterostructures

    Science.gov (United States)

    Jiang, H. W.; Yablonovitch, Eli

    2001-07-01

    The electron spin resonance (ESR) of two-dimensional electrons is investigated in a gated GaAs/AlGaAs heterostructure. We found that the ESR resonance frequency can be tuned by means of a gate voltage. The front and back gates of the heterostructure produce opposite g-factor shift, suggesting that electron g factor is being electrostatically controlled by shifting the equilibrium position of the electron wave function from one epitaxial layer to another with different g factors.

  12. Spin State Control using Oxide Interfaces in LaCoO3-based Heterostructures

    Science.gov (United States)

    Lee, Sangjae; Disa, Ankit; Walker, Frederick; Ahn, Charles

    The flexibility of the spin degree of freedom of the Co 3d orbitals in LaCoO3 suggests that they can be changed through careful design of oxide heterostructures. Interfacial coupling and dimensional confinement can be used to control the magnetic exchange, crystal fields, and Hund's coupling, through orbital and charge reconstructions. These parameters control the balance between multiple spin configurations, thereby modifying the magnetic ordering of LaCoO3. We study (LaCoO3)m /(LaTiO3)2 heterostructures grown by molecular beam epitaxy, which allow interfacial charge transfer from Ti to Co, in addition to structural and dimensional constraints. The electronic polarization at the interface and consequent structural distortions suppress the ferromagnetism in the LaCoO3 layers. This effect extends well beyond the interface, with ferromagnetic order absent up to LaCoO3 layer thickness of m =10. We compare the properties of the LaCoO3/LaTiO3heterostructureswithLaCoO3/SrTiO3, to untangle how charge transfer and structural modifications control the spin and magnetic configuration in cobaltates.

  13. Graphene-WS2 heterostructures for tunable spin injection and spin transport

    Science.gov (United States)

    Omar, S.; van Wees, B. J.

    2017-02-01

    We report the first measurements of spin injection into graphene through a 20-nm-thick tungsten disulphide (WS2) layer, along with a modified spin relaxation time (τs) in graphene in the WS2 environment, via spin-valve and Hanle spin-precession measurements, respectively. First, during the spin injection into graphene through a WS2-graphene interface, we can tune the interface resistance at different current bias and modify the spin injection efficiency, in a correlation with the conductivity-mismatch theory. Temperature assisted tunneling is identified as a dominant mechanism for the charge transport across the interface. Second, we measure the spin transport in graphene, underneath the WS2 crystal, and observe a significant reduction in the τs down to 17 ps in graphene in the WS2 covered region, compared to that in its pristine state. The reduced τs indicates the WS2-proximity induced additional dephasing of the spins in graphene.

  14. Room temperature magnetization switching in topological insulator-ferromagnet heterostructures by spin-orbit torques.

    Science.gov (United States)

    Wang, Yi; Zhu, Dapeng; Wu, Yang; Yang, Yumeng; Yu, Jiawei; Ramaswamy, Rajagopalan; Mishra, Rahul; Shi, Shuyuan; Elyasi, Mehrdad; Teo, Kie-Leong; Wu, Yihong; Yang, Hyunsoo

    2017-11-08

    Topological insulators with spin-momentum-locked topological surface states are expected to exhibit a giant spin-orbit torque in the topological insulator/ferromagnet systems. To date, the topological insulator spin-orbit torque-driven magnetization switching is solely reported in a Cr-doped topological insulator at 1.9 K. Here we directly show giant spin-orbit torque-driven magnetization switching in a Bi2Se3/NiFe heterostructure at room temperature captured using a magneto-optic Kerr effect microscope. We identify a large charge-to-spin conversion efficiency of ~1-1.75 in the thin Bi2Se3 films, where the topological surface states are dominant. In addition, we find the current density required for the magnetization switching is extremely low, ~6 × 105 A cm-2, which is one to two orders of magnitude smaller than that with heavy metals. Our demonstration of room temperature magnetization switching of a conventional 3d ferromagnet using Bi2Se3 may lead to potential innovations in topological insulator-based spintronic applications.

  15. Theoretical models of Rashba spin splitting in asymmetric SrTiO3-based heterostructures

    Science.gov (United States)

    van Heeringen, L. W.; McCollam, A.; de Wijs, G. A.; Fasolino, A.

    2017-04-01

    Rashba spin splitting in two-dimensional (2D) semiconductor systems is generally calculated in a k .p Luttinger-Kohn approach where the spin splitting due to asymmetry emerges naturally from the bulk band structure. In recent years, several new classes of 2D systems have been discovered where electronic correlations are believed to have an important role. In these correlated systems, the effects of asymmetry leading to Rashba splitting have typically been treated phenomenologically. We compare these two approaches for the case of 2D electron systems in SrTiO3-based heterostructures, and find that the two models produce fundamentally different behavior in regions of the Brillouin zone that are particularly relevant for magnetotransport. Our results demonstrate the importance of identifying the correct approach in the quantitative interpretation of experimental data, and are likely to be relevant to a range of 2D systems in correlated materials.

  16. Spin Qubits in GaAs Heterostructures and Gating of InAs Nanowires for Lowtemperature Measurements

    DEFF Research Database (Denmark)

    Nissen, Peter Dahl

    voltages for barrier induction (Vg 􀀀1 to 􀀀2V), but low temperature gate sweeps suggest that device stability could be affected by the differences in device processing for the two gate geometries. For the GaAs heterostructure we investigate two new ideas for realizing spin qubits...

  17. Boosting the superconducting spin valve effect in a metallic superconductor/ferromagnet heterostructure

    Energy Technology Data Exchange (ETDEWEB)

    Leksin, Pavel [Leibniz Institute for Solid State and Materials Research Dresden, IFW Dresden (Germany); Zavoisky Physical-Technical Institute, Russian Academy of Sciences, Kazan (Russian Federation); Kamashev, Andrey; Garifullin, Ilgiz [Zavoisky Physical-Technical Institute, Russian Academy of Sciences, Kazan (Russian Federation); Schumann, Joachim; Kataev, Vladislav; Thomas, Juergen [Leibniz Institute for Solid State and Materials Research Dresden, IFW Dresden (Germany); Buechner, Bernd [Leibniz Institute for Solid State and Materials Research Dresden, IFW Dresden (Germany); Technical University Dresden (Germany)

    2016-07-01

    We demonstrate a crucial role of the morphology of the superconducting layer for the operation of the multilayer S/F1/F2 spin valve. For that, we studied two types of superconducting spin valve heterostructures, with a rough and with a smooth superconducting layer, respectively, with transmission electron microscopy in combination with transport and magnetic characterization. We have found that the quality of the S/F interface is not critical for the S/F proximity effect as regards the suppression of the critical temperature of the S layer. However, it appears to be of a paramount importance for the performance of the S/F1/F2 spin valve. The magnitude of the conventional superconducting spin valve effect significantly increases, when the morphology of the S layer is changed from the type of overlapping islands to a smooth one. We attribute this drastic effect to a homogenization of the Green function of the superconducting condensate over the S/F interface in the S/F1/F2 valve with a smooth S layer surface.

  18. Thickness dependence of the triplet spin-valve effect in superconductor-ferromagnet-ferromagnet heterostructures.

    Science.gov (United States)

    Lenk, Daniel; Zdravkov, Vladimir I; Kehrle, Jan-Michael; Obermeier, Günter; Ullrich, Aladin; Morari, Roman; Krug von Nidda, Hans-Albrecht; Müller, Claus; Kupriyanov, Mikhail Yu; Sidorenko, Anatolie S; Horn, Siegfried; Deminov, Rafael G; Tagirov, Lenar R; Tidecks, Reinhard

    2016-01-01

    In nanoscale layered S/F1/N/F2/AF heterostructures, the generation of a long-range, odd-in-frequency spin-projection one triplet component of superconductivity, arising at non-collinear alignment of the magnetizations of F1 and F2, exhausts the singlet state. This yields the possibility of a global minimum of the superconducting transition temperature T c, i.e., a superconducting triplet spin-valve effect, around mutually perpendicular alignment. The superconducting triplet spin valve is realized with S = Nb a singlet superconductor, F1 = Cu41Ni59 and F2 = Co ferromagnetic metals, AF = CoO x an antiferromagnetic oxide, and N = nc-Nb a normal conducting (nc) non-magnetic metal, which serves to decouple F1 and F2. The non-collinear alignment of the magnetizations is obtained by applying an external magnetic field parallel to the layers of the heterostructure and exploiting the intrinsic perpendicular easy-axis of the magnetization of the Cu41Ni59 thin film in conjunction with the exchange bias between CoO x and Co. The magnetic configurations are confirmed by superconducting quantum interference device (SQUID) magnetic moment measurements. The triplet spin-valve effect has been investigated for different layer thicknesses, d F1, of F1 and was found to decay with increasing d F1. The data is described by an empirical model and, moreover, by calculations using the microscopic theory. The long-range triplet component of superconducting pairing is generated from the singlet component mainly at the N/F2 interface, where the amplitude of the singlet component is suppressed exponentially with increasing distance d F1. The decay length of the empirical model is found to be comparable to twice the electron mean free path of F1 and, thus, to the decay length of the singlet component in F1. Moreover, the obtained data is in qualitative agreement with the microscopic theory, which, however, predicts a (not investigated) breakdown of the triplet spin-valve effect for d F1 smaller

  19. Thickness dependence of the triplet spin-valve effect in superconductor–ferromagnet–ferromagnet heterostructures

    Directory of Open Access Journals (Sweden)

    Daniel Lenk

    2016-07-01

    Full Text Available Background: In nanoscale layered S/F1/N/F2/AF heterostructures, the generation of a long-range, odd-in-frequency spin-projection one triplet component of superconductivity, arising at non-collinear alignment of the magnetizations of F1 and F2, exhausts the singlet state. This yields the possibility of a global minimum of the superconducting transition temperature Tc, i.e., a superconducting triplet spin-valve effect, around mutually perpendicular alignment.Results: The superconducting triplet spin valve is realized with S = Nb a singlet superconductor, F1 = Cu41Ni59 and F2 = Co ferromagnetic metals, AF = CoOx an antiferromagnetic oxide, and N = nc-Nb a normal conducting (nc non-magnetic metal, which serves to decouple F1 and F2. The non-collinear alignment of the magnetizations is obtained by applying an external magnetic field parallel to the layers of the heterostructure and exploiting the intrinsic perpendicular easy-axis of the magnetization of the Cu41Ni59 thin film in conjunction with the exchange bias between CoOx and Co. The magnetic configurations are confirmed by superconducting quantum interference device (SQUID magnetic moment measurements. The triplet spin-valve effect has been investigated for different layer thicknesses, dF1, of F1 and was found to decay with increasing dF1. The data is described by an empirical model and, moreover, by calculations using the microscopic theory.Conclusion: The long-range triplet component of superconducting pairing is generated from the singlet component mainly at the N/F2 interface, where the amplitude of the singlet component is suppressed exponentially with increasing distance dF1. The decay length of the empirical model is found to be comparable to twice the electron mean free path of F1 and, thus, to the decay length of the singlet component in F1. Moreover, the obtained data is in qualitative agreement with the microscopic theory, which, however, predicts a (not investigated breakdown of the

  20. Delta(X)-L intervalley mixing in SiGe heterostructures for electron spin manipulation

    Science.gov (United States)

    Kiselev, A. A.; Kim, K. W.; Yablonovitch, E.

    2004-03-01

    The technical ability to manipulate quantum information can result from the intervalley mixing in heterostructures. A SiGe structure with two active layers, Si-rich and Ge-rich can serve as an example. g factors for Delta and L electrons are way different, so shifting electron across the interface can be used for the practical spin manipulation, with the degree of modulation governed by the strength of intervalley mixing. We propose a general approach to the problem of intervalley mixing of electron states in heterostructures in the framework of transparent effective mass method. Calculation of the mixing potentials can be done, considering changes in the constituent concentrations of individual heterolayers from some "virtual crystal level" as a bunch of microscopic single-ion perturbations. For the Delta and L states at the (001) interface, the magnitude of mixing is random and residually small. For the (111) interface, large mixing does take place, but only for one of the higher confinement-shifted L valleys. The (311) interface presents a solution, allowing, simultaneously, to (i) lift degeneracy of the Delta states; (ii) lift degeneracy of the L states, and (iii) allow strong mixing between lowest L and Delta states.

  1. Investigation of the field dependent spin structure of exchange coupled magnetic heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Gurieva, Tatiana

    2016-05-15

    This thesis describes the investigation of the field dependent magnetic spin structure of an antiferromagnetically (AF) coupled Fe/Cr heterostructure sandwiched between a hardmagnetic FePt buffer layer and a softmagnetic Fe top layer. The depth-resolved experimental studies of this system were performed via Magneto-optical Kerr effect (MOKE), Vibrating Sample Magnetometry (VSM) and various measuring methods based on nuclear resonant scattering (NRS) technique. Nucleation and evolution of the magnetic spiral structure in the AF coupled Fe/Cr multilayer structure in an azimuthally rotating external magnetic field were observed using NRS. During the experiment a number of time-dependent magnetic side effects (magnetic after-effect, domain-wall creep effect) caused by the non-ideal structure of a real sample were observed and later explained. Creation of the magnetic spiral structure in rotating external magnetic field was simulated using a one-dimensional micromagnetic model.The cross-sectional magnetic X-ray diffraction technique was conceived and is theoretically described in the present work. This method allows to determine the magnetization state of an individual layer in the magnetic heterostructure. It is also applicable in studies of the magnetic structure of tiny samples where conventional x-ray reflectometry fails.

  2. Electron-spin-resonance transistors for quantum computing in silicon-germanium heterostructures

    Science.gov (United States)

    Vrijen, Rutger; Yablonovitch, Eli; Wang, Kang; Jiang, Hong Wen; Balandin, Alex; Roychowdhury, Vwani; Mor, Tal; Divincenzo, David

    2000-07-01

    We apply the full power of modern electronic band-structure engineering and epitaxial heterostructures to design a transistor that can sense and control a single-donor electron spin. Spin-resonance transistors may form the technological basis for quantum information processing. One- and two-qubit operations are performed by applying a gate bias. The bias electric field pulls the electron wave function away from the dopant ion into layers of different alloy composition. Owing to the variation of the g factor (Si:g=1.998,Ge:g=1.563), this displacement changes the spin Zeeman energy, allowing single-qubit operations. By displacing the electron even further, the overlap with neighboring qubits is affected, which allows two-qubit operations. Certain silicon-germanium alloys allow a qubit spacing as large as 200 nm, which is well within the capabilities of current lithographic techniques. We discuss manufacturing limitations and issues regarding scaling up to a large size computer.

  3. Spin-orbit torque-driven magnetization switching in 2D-topological insulator heterostructure

    Science.gov (United States)

    Soleimani, Maryam; Jalili, Seifollah; Mahfouzi, Farzad; Kioussis, Nicholas

    2017-02-01

    Charge pumping and spin-orbit torque (SOT) are two reciprocal phenomena widely studied in ferromagnet (FM)/topological insulator (TI) heterostructures. However, the SOT and its corresponding switching phase diagram for a FM island in proximity to a two-dimensional topological insulator (2DTI) has not been explored yet. We have addressed these features, using the recently developed adiabatic expansion of time-dependent nonequilibrium Green's function (NEGF) in the presence of both precessing magnetization and bias voltage. We have calculated the angular and spatial dependence of different components of the SOT on the FM island. We determined the switching phase diagram of the FM for different orientations of the easy axis. The results can be used as a guideline for the future experiments on such systems.

  4. Spin and Charge Transport in 2D Materials and Magnetic Insulator/Metal Heterostructures

    Science.gov (United States)

    Amamou, Walid

    Spintronic devices are very promising for future information storage, logic operations and computation and have the potential to replace current CMOS technology approaching the scaling limit. In particular, the generation and manipulation of spin current enables the integration of storage and logic within the same circuit for more powerful computing architectures. In this thesis, we examine the manipulation of spins in 2D materials such as graphene and metal/magnetic insulator heterostructures. In particular, we investigate the feasibility for achieving magnetization switching of a nanomagnet using graphene as a nonmagnetic channel material for All Spin Logic Device applications. Using in-situ MBE deposition of nanomagnet on graphene spin valve, we demonstrate the presence of an interfacial spin dephasing at the interface between the graphene and the nanomagnet. By introducing a Cu spacer between the nanomagnet and graphene, we demonstrate that this interfacial effect is related to an exchange interaction between the spin current and the disordered magnetic moment of the nanomagnet in the first monolayer. In addition to the newly discovered interfacial spin relaxation effect, the extracted contact resistance area product of the nanomagnet/graphene interface is relatively high on the order of 1Omicrom2. In practice, reducing the contact resistance will be as important as eliminating the interfacial relaxation in order to achieve magnetization switching. Furthermore, we examine spin manipulation in a nonmagnetic Pt using an internal magnetic exchange field produced by the adjacent magnetic insulator CoFe2O4 grown by MBE. Here, we report the observation of a strong magnetic proximity effect of Pt deposited on top of a perpendicular magnetic anisotropy (PMA) inverse spinel material Cobalt Ferrite (CFO, CoFe 2O4). The CFO was grown by MBE and its magnetization was characterized by Vibrating Sample Magnetometry (VSM) demonstrating the strong out of plane magnetic

  5. Spin-orbit torque in 3D topological insulator-ferromagnet heterostructure: crossover between bulk and surface transport

    KAUST Repository

    Ghosh, Sumit

    2017-11-29

    Current-driven spin-orbit torques are investigated in a heterostructure composed of a ferromagnet deposited on top of a three dimensional topological insulator using the linear response formalism. We develop a tight-binding model of the heterostructure adopting a minimal interfacial hybridization scheme that promotes induced magnetic exchange on the topological surface states, as well as induced Rashba-like spin-orbit coupling in the ferromagnet. Therefore, our model accounts for spin Hall effect from bulk states together with inverse spin galvanic and magnetoelectric effects at the interface on equal footing. By varying the transport energy across the band structure, we uncover a crossover from surface-dominated to bulk-dominated transport regimes. We show that the spin density profile and the nature of the spin-orbit torques differ substantially in both regimes. Our results, which compare favorably with experimental observations, demonstrate that the large damping torque reported recently is more likely attributed to interfacial magnetoelectric effect, while spin Hall torque remains small even in the bulk-dominated regime.

  6. Materials Development and Spin Transport Study of Magnetic Insulator Based Heterostructures

    Science.gov (United States)

    Tang, Chi

    The subfield of magnetic insulator (MI) based spintronics is playing a substantial role in modern solid state physics research. Spin current in the MI is propagated in spin wave with a much longer decay length than spin-polarized carriers in conducting ferromagnet. In the MI-based hetereostructures, the adjacent non-magnetic materials can be magnetized in proximity of MI. Therefore, it is a promising system to study exotic transport phenomena such as quantum Anomalous Hall effect in topological insulator and graphene. Rare-earth Iron garnet (ReIG), a class of magnetic insulators with large electronic bandgap and high Curie temperature, stands out among various magnetic insulator materials and have attracted a great deal of attention in recent magnetic insulator based spintronics research. The first chapter of this dissertation gives a brief introduction to the spintronics research by introducing some essential concepts in the spintronics field and the most recent spin transport phenomena. The second chapter of this dissertation summarizes my work in the materials development of ReIG ferrimagnetic insulators, including exquisite control of high quality ultra-flat yttrium iron garnet (YIG) thin films with extremely low magnetic damping and engineering of strain induced robust perpendicular magnetic anisotropy in thulium iron garnet (TIG) and Bi-doped YIG films. The last chapter of this dissertation shows a systematic study in various ReIG based heterostructures, mainly divided into groups: ReIG (YIG & TIG)/heavy metal bilayers (Pd & Pt) and ReIG (YIG & TIG)/Dirac systems (graphene & topological insulator). The magneto-transport study disentangles the contribution from a spin current origin and proximity induced magnetism. Furthermore, the demonstration in the proximity coupling induced high-temperature ferromagnetic phase in low-dimensional Dirac systems, i.e. graphene and topological insulator surface states, provides new possibilities in the future spintronics

  7. Spin Qubits in GaAs Heterostructures and Gating of InAs Nanowires for Lowtemperature Measurements

    DEFF Research Database (Denmark)

    Nissen, Peter Dahl

    distant qubits. This thesis presents electric measurement on two of the materials systems currently at the forefront of the spin qubit race, namely InAs nanowires and GaAs/AlGaAs heterostructures. For the InAs nanowires we investigate dierent gating geometries towards the goal of dening stable quantum...... dots in the nanowire at mK temperatures. Three types of local gates are analyzed; narrow gates (50100nm) located on top of or below the nanowire, and wide gates overlapping the interfaces between nanowire and source and drain electrodes. We nd that applying negative potentials to the local gate...... voltages for barrier induction (Vg 􀀀1 to 􀀀2V), but low temperature gate sweeps suggest that device stability could be affected by the differences in device processing for the two gate geometries. For the GaAs heterostructure we investigate two new ideas for realizing spin qubits...

  8. L-valley electrons in SiGe heterostructures: highly anisotropic and tunable Zeeman and Rashba-like spin splittings

    Science.gov (United States)

    Kiselev, A. A.; Baron, F. A.; Kim, K. W.; Wang, K. L.; Yablonovitch, E.

    2005-06-01

    We have conducted a detailed and systematic analysis of Zeeman and Rashba-like (structure-asymmetry-induced) spin splittings in SiGe heterostructures. The calculations were performed in the framework of a relevant kp model, developed specifically for the L point states of the group IV semiconductors. Effects of the alloy composition, crystallographic orientation, spatial confinement, strain, and electric field are accounted for and documented for a realistic structure design. Notable Rashba effect, considerable anisotropy and deviation of the g tensor components from their respective bulk values make the SiGe structures a friendly choice for the effective spin manipulation.

  9. Magneto-optical investigation of spin-orbit torques in metallic and insulating magnetic heterostructures.

    Science.gov (United States)

    Montazeri, Mohammad; Upadhyaya, Pramey; Onbasli, Mehmet C; Yu, Guoqiang; Wong, Kin L; Lang, Murong; Fan, Yabin; Li, Xiang; Khalili Amiri, Pedram; Schwartz, Robert N; Ross, Caroline A; Wang, Kang L

    2015-12-08

    Manipulating magnetism by electric current is of great interest for both fundamental and technological reasons. Much effort has been dedicated to spin-orbit torques (SOTs) in metallic structures, while quantitative investigation of analogous phenomena in magnetic insulators remains challenging due to their low electrical conductivity. Here we address this challenge by exploiting the interaction of light with magnetic order, to directly measure SOTs in both metallic and insulating structures. The equivalency of optical and transport measurements is established by investigating a heavy-metal/ferromagnetic-metal device (Ta/CoFeB/MgO). Subsequently, SOTs are measured optically in the contrasting case of a magnetic-insulator/heavy-metal (YIG/Pt) heterostructure, where analogous transport measurements are not viable. We observe a large anti-damping torque in the YIG/Pt system, revealing its promise for spintronic device applications. Moreover, our results demonstrate that SOT physics is directly accessible by optical means in a range of materials, where transport measurements may not be possible.

  10. Superconducting spin valves based on epitaxial Fe/V-hybrid thin film heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Nowak, Gregor

    2010-12-10

    This study presents a systematic investigation of the SSV effect in FM/SC/FM and FM/N/FM/SC heterostructures. Before investigating the actual SSV effect, we first pre-analyzed structural, magnetic and superconducting properties of the Fe/V system. In these preliminary studies we demonstrated, that epitaxial Fe/V heterostructures of superior crystalline quality can be grown by DC sputter deposition. With a Fe/V interface thickness of only one monolayer, the chemical separation of the Fe and V layers is extremely sharp. Moreover, the magnetic investigation showed that from thicknesses of two Fe(001) monolayers on the Fe layers in the superlattice possess a magnetic moment. Furthermore, we demonstrated the interlayer exchange coupling as oscillatory function of the V interlayer thickness. The investigations of the superconducting parameters of the Fe/V system revealed a non-monotonic T{sub S} vs. d{sub Fe} dependence in sample series (1). This observation proves the presence of the FM/SC proximity effect. The studies of various heterostructures of the design AFM/FM/SC/FM revealed a strong counteracting influence on the SSV effect, the stray field effect. The sample containing Fe{sub 25}V{sub 75} alloy layers, has the highest ratio of Cooper pair coherence length and superconductor thickness (ξ{sub S})/(d{sub S}), and its superconducting transition temperature is comparable to the sample with Fe{sub 35}V{sub 65} alloy layers. Nevertheless, the SSV effect in sample Fe{sub 25}V{sub 75} with alloy layers is much smaller than in sample with Fe{sub 35}V{sub 65} alloy layers. For a high-performance superconducting spin valve based on a FM1/SC/FM2 heterostructure at least four parameters have to be optimized simultaneously. 1. The magnetic domain size in FM1 and FM2 has to be as large as possible in order to reduce the stray field effect resulting from magnetization components in the FM domain walls perpendicular to the SC layer. 2. When using ferromagnetic alloys as

  11. Materials optimization and ghz spin dynamics of metallic ferromagnetic thin film heterostructures

    Science.gov (United States)

    Cheng, Cheng

    Metallic ferromagnetic (FM) thin film heterostructures play an important role in emerging magnetoelectronic devices, which introduce the spin degree of freedom of electrons into conventional charge-based electronic devices. As the majority of magnetoelectronic devices operate in the GHz frequency range, it is critical to understand the high-frequency magnetization dynamics in these structures. In this thesis, we start with the static magnetic properties of FM thin films and their optimization via the field-sputtering process incorporating a specially designed in-situ electromagnet. We focus on the origins of anisotropy and hysteresis/coercivity in soft magnetic thin films, which are most relevant to magentic susceptibility and power dissipation in applications in the sub-GHz frequency regime, such as magnetic-core integrated inductors. Next we explore GHz magnetization dynamics in thin-film heterostructures, both in semi-infinite samples and confined geometries. All investigations are rooted in the Landau-Lifshitz-Gilbert (LLG) equation, the equation of motion for magnetization. The phenomenological Gilbert damping parameter in the LLG equation has been interpreted, since the 1970's, in terms of the electrical resistivity. We present the first interpretation of the size effect in Gilbert damping in single metallic FM films based on this electron theory of damping. The LLG equation is intrinsically nonlinear, which provides possibilities for rf signal processing. We analyze the frequency doubling effect at small-angle magnetization precession from the first-order expansion of the LLG equation, and demonstrate second harmonic generation from Ni81 Fe19 (Permalloy) thin film under ferromagnetic resonance (FMR), three orders of magnitude more efficient than in ferrites traditionally used in rf devices. Though the efficiency is less than in semiconductor devices, we provide field- and frequency-selectivity in the second harmonic generation. To address further the

  12. Electric-field tunable spin waves in PMN-PT/NiFe heterostructure: Experiment and micromagnetic simulations

    Energy Technology Data Exchange (ETDEWEB)

    Ziȩtek, Slawomir, E-mail: zietek@agh.edu.pl [AGH University of Science and Technology, Department of Electronics, Al. Mickiewicza 30, 30-059 Kraków (Poland); Chȩciński, Jakub [AGH University of Science and Technology, Department of Electronics, Al. Mickiewicza 30, 30-059 Kraków (Poland); AGH University of Science and Technology, Faculty of Physics and Applied Computer Science, Al. Mickiewicza 30, 30-059 Kraków (Poland); Frankowski, Marek; Skowroński, Witold; Stobiecki, Tomasz [AGH University of Science and Technology, Department of Electronics, Al. Mickiewicza 30, 30-059 Kraków (Poland)

    2017-04-15

    We present a comprehensive theoretical and experimental study of voltage-controlled standing spin waves resonance (SSWR) in PMN-PT/NiFe multiferroic heterostructures patterned into microstrips. A spin-diode technique was used to observe ferromagnetic resonance (FMR) mode and SSWR in NiFe strip mechanically coupled with a piezoelectric substrate. Application of an electric field to a PMN-PT creates a strain in permalloy and thus shifts the FMR and SSWR fields due to the magnetostriction effect. The experimental results are compared with micromagnetic simulations and a good agreement between them is found for dynamics of FMR and SSWR with and without electric field. Moreover, micromagnetic simulations enable us to discuss the amplitude and phase spatial distributions of FMR and SSWR modes, which are not directly observable by means of spin diode detection technique.

  13. Tunneling conductance for Majorana fermions in spin-orbit coupled semiconductor-superconductor heterostructures using superconducting leads

    Science.gov (United States)

    Sharma, Girish; Tewari, Sumanta

    2016-05-01

    It has been recently pointed out that the use of a superconducting (SC) lead instead of a normal metal lead can suppress the thermal broadening effects in tunneling conductance from Majorana fermions, helping reveal the quantized conductance of 2 e2/h . In this paper we discuss the specific case of tunneling conductance with SC leads of spin-orbit coupled semiconductor-superconductor (SM-SC) heterostructures in the presence of a Zeeman field, a system which has been extensively studied both theoretically and experimentally using a metallic lead. We examine the d I /d V spectra using a SC lead for different sets of physical parameters including temperature, tunneling strength, wire length, magnetic field, and induced SC pairing potential in the SM nanowire. We conclude that in a finite wire the Majorana splitting energy Δ E , which has nontrivial dependence on these physical parameters, remains responsible for the d I /d V peak broadening, even when the temperature broadening is suppressed by the SC gap in the lead. In a finite wire the signatures of Majorana fermions with a SC lead are oscillations of quasi-Majorana peaks about bias V =±Δlead , in contrast to the case of metallic leads where such oscillations are about zero bias. Our results will be useful for analysis of future experiments on SM-SC heterostructures using SC leads.

  14. Light-induced magnetization changes in a coordination polymer heterostructure of a Prussian blue analogue and a Hofmann-like Fe(II) spin crossover compound.

    Science.gov (United States)

    Gros, Corey R; Peprah, Marcus K; Hosterman, Brian D; Brinzari, Tatiana V; Quintero, Pedro A; Sendova, Mariana; Meisel, Mark W; Talham, Daniel R

    2014-07-16

    Coordination polymer thin film heterostructures of the Prussian blue analogue Ni(II)b[Cr(III)(CN)6](0.7)·nH2O (NiCr-PBA) and the 3D Hofmann-like spin crossover compound Fe(azpy)[Pt(CN)4]·xH2O {azpy = 4,4'-azopyridine} have been developed, and spin transition properties have been characterized via SQUID magnetometry and Raman spectroscopy. The magnetic response of the ferromagnetic NiCr-PBA layer (T(c) ≈ 70 K) can be altered by inducing the LIESST effect (light-induced excited spin state trapping) in the coupled paramagnetic Fe(II) spin crossover material. Whereas an increase in magnetization is measured for the single-phase Fe(azpy)[Pt(CN)4]·xH2O, a decrease in magnetization is observed for the heterostructure. These results indicate the LIESST effect alone cannot account for the sign and magnitude of the magnetization change in the heterostructure, but the temperature profile of the magnetization shows that significant changes in the NiCr-PBA network are correlated to the spin state of the Hofmann-like SCO network.

  15. Strong electron-hole symmetric Rashba spin-orbit coupling in graphene/monolayer transition metal dichalcogenide heterostructures

    Science.gov (United States)

    Yang, Bowen; Lohmann, Mark; Barroso, David; Liao, Ingrid; Lin, Zhisheng; Liu, Yawen; Bartels, Ludwig; Watanabe, Kenji; Taniguchi, Takashi; Shi, Jing

    2017-07-01

    Despite its extremely weak intrinsic spin-orbit coupling (SOC), graphene has been shown to acquire considerable SOC by proximity coupling with exfoliated transition metal dichalcogenides (TMDs). Here we demonstrate strong induced Rashba SOC in graphene that is proximity coupled to a monolayer TMD film, Mo S2 or WS e2 , grown by chemical-vapor deposition with drastically different Fermi level positions. Graphene/TMD heterostructures are fabricated with a pickup-transfer technique utilizing hexagonal boron nitride, which serves as a flat template to promote intimate contact and therefore a strong interfacial interaction between TMD and graphene as evidenced by quenching of the TMD photoluminescence. We observe strong induced graphene SOC that manifests itself in a pronounced weak-antilocalization (WAL) effect in the graphene magnetoconductance. The spin-relaxation rate extracted from the WAL analysis varies linearly with the momentum scattering time and is independent of the carrier type. This indicates a dominantly Dyakonov-Perel spin-relaxation mechanism caused by the induced Rashba SOC. Our analysis yields a Rashba SOC energy of ˜1.5 meV in graphene/WS e2 and ˜0.9 meV in graphene/Mo S2 . The nearly electron-hole symmetric nature of the induced Rashba SOC provides a clue to possible underlying SOC mechanisms.

  16. An origin behind Rashba spin splitting within inverted doped sGe heterostructures

    Science.gov (United States)

    Hassan, A. H. A.; Morris, R. J. H.; Mironov, O. A.; Gabani, S.; Dobbie, A.; Leadley, D. R.

    2017-01-01

    In this paper, we demonstrate why cubic Rashba spin splitting is observed within inverted doped strained germanium (sGe) hetrostructures. Magnetotransport measurements showed beating within the SdH oscillation, with fast Fourier analysis revealing cubic Rashba spin splitting to be present. A cubic Rashba coefficient of β=7.97 ×10-29 eVm3 and a spin-splitting energy of Δ=1.17 meV were determined. The source of the cubic Rashba spin splitting was identified from a combination of ultra low energy secondary ion mass spectrometry analysis and subsequent band structure modelling using Nextnano3. Ultra-low energy secondary ion mass spectrometry revealed an unintentional, highly B doped near surface region accounted for structure inversion asymmetry, whereas subsequent band structure modelling using Nextnano3 demonstrates how this asymmetric B doping generates structural inversion asymmetry within the sGe QW structure and cubic Rashba spin splitting realized.

  17. Inversion of Spin Signal and Spin Filtering in Ferromagnet/Hexagonal Boron Nitride-Graphene van der Waals Heterostructures

    NARCIS (Netherlands)

    Venkata Kamalakar, M; Dankert, Andre; Kelly, Paul J.; Dash, S.P.

    2016-01-01

    Two dimensional atomically thin crystals of graphene and its insulating isomorph hexagonal boron nitride (h-BN) are promising materials for spintronic applications. While graphene is an ideal medium for long distance spin transport, h-BN is an insulating tunnel barrier that has potential for

  18. Spin transport in two-layer-CVD-hBN/graphene/hBN heterostructures

    Science.gov (United States)

    Gurram, M.; Omar, S.; Zihlmann, S.; Makk, P.; Li, Q. C.; Zhang, Y. F.; Schönenberger, C.; van Wees, B. J.

    2018-01-01

    We study room-temperature spin transport in graphene devices encapsulated between a layer-by-layer-stacked two-layer-thick chemical vapor deposition (CVD) grown hexagonal boron nitride (hBN) tunnel barrier, and a few-layer-thick exfoliated-hBN substrate. We find mobilities and spin-relaxation times comparable to that of SiO2 substrate-based graphene devices, and we obtain a similar order of magnitude of spin relaxation rates for both the Elliott-Yafet and D'Yakonov-Perel' mechanisms. The behavior of ferromagnet/two-layer-CVD-hBN/graphene/hBN contacts ranges from transparent to tunneling due to inhomogeneities in the CVD-hBN barriers. Surprisingly, we find both positive and negative spin polarizations for high-resistance two-layer-CVD-hBN barrier contacts with respect to the low-resistance contacts. Furthermore, we find that the differential spin-injection polarization of the high-resistance contacts can be modulated by dc bias from -0.3 to +0.3 V with no change in its sign, while its magnitude increases at higher negative bias. These features point to the distinctive spin-injection nature of the two-layer-CVD-hBN compared to the bilayer-exfoliated-hBN tunnel barriers.

  19. Spin-Orbit Coupling in AlGaN/AlN/GaN Heterostructures with a Polarization Induced Two-Dimensional Electron Gas

    Science.gov (United States)

    Cheng, H.; Kurdak, C.; Biyikli, N.; Ozgur, U.; Morkoc, H.; Litvinov, V. I.

    2007-03-01

    Spin-orbit coupling is investigated by weak antilocalization and Shubnikov-de Haas measurements in wurtzite AlxGa1-xN/AlN/GaN heterostructures with a polarization induced two dimensional electron gas. By employing the persistent photoconductivity effect and by using five different heterostructures with different Al compositions, we cover a carrier density range extending from 0.8x10^12 cm-2 to 10.6x10^12 cm-2. We determine electron splitting energies for different carrier densities by analyzing the weak antilocalization measurements using the Iordanskii, Lyanda-Geller, and Pikus theory. We find the spin splitting energies do not scale linearly with the Fermi wavevector kF at high carrier densities. By fitting the spin splitting energies to a form ESS=2(αkF+γkF^3) we extract linear and cubic spin-orbit coupling parameters α=5.13x10-13 eV m and γ=1.2x10-31eV m^3, respectively. The cubic spin-orbit coupling parameter is purely due to the bulk inversion asymmetry of the wurtzite crystal and has not been previously measured for the GaN system.

  20. Spin-orbit torque in Cr/CoFeAl/MgO and Ru/CoFeAl/MgO epitaxial magnetic heterostructures

    Directory of Open Access Journals (Sweden)

    Zhenchao Wen

    2016-05-01

    Full Text Available We study the spin-orbit torque (SOT effective fields in Cr/CoFeAl/MgO and Ru/CoFeAl/MgO magnetic heterostructures using the adiabatic harmonic Hall measurement. High-quality perpendicular-magnetic-anisotropy CoFeAl layers were grown on Cr and Ru layers. The magnitudes of the SOT effective fields were found to significantly depend on the underlayer material (Cr or Ru as well as their thicknesses. The damping-like longitudinal effective field (ΔHL increases with increasing underlayer thickness for all heterostructures. In contrast, the field-like transverse effective field (ΔHT increases with increasing Ru thickness while it is almost constant or slightly decreases with increasing Cr thickness. The sign of ΔHL observed in the Cr-underlayer devices is opposite from that in the Ru-underlayer devices while ΔHT shows the same sign with a small magnitude. The opposite directions of ΔHL indicate that the signs of spin Hall angle in Cr and Ru are opposite, which are in good agreement with theoretical predictions. These results show sizable contribution from SOT even for elements with small spin orbit coupling such as 3d Cr and 4d Ru.

  1. Designing in-plane heterostructures of quantum spin Hall insulators from first principles: 1T'-MoS2 with adsorbates

    DEFF Research Database (Denmark)

    Olsen, Thomas

    2016-01-01

    Interfaces between normal and topological insulators are bound to host metallic states that are protected by time-reversal symmetry and are therefore robust against disorder and interface reconstruction. Two-dimensional topological insulators (quantum spin Hall insulators) offer a unique opportun....... This is in sharp contrast to topological edge states, which typically exhibit strong dispersion that are sensitive to a particular edge termination. The heterostructure is also suggestive of a simple design of one-dimensional metallic networks in sheets of 1T'-MoS2....

  2. Spin valve-like magnetic tunnel diode exhibiting giant positive junction magnetoresistance at low temperature in Co2MnSi/SiO2/p-Si heterostructure

    Science.gov (United States)

    Maji, Nilay; Kar, Uddipta; Nath, T. K.

    2018-02-01

    The rectifying magnetic tunnel diode has been fabricated by growing Co2MnSi (CMS) Heusler alloy film carefully on a properly cleaned p-Si (100) substrate with the help of electron beam physical vapor deposition technique and its structural, electrical and magnetic properties have been experimentally investigated in details. The electronic- and magneto-transport properties at various isothermal conditions have been studied in the temperature regime of 78-300 K. The current-voltage ( I- V) characteristics of the junction show an excellent rectifying magnetic tunnel diode-like behavior throughout that temperature regime. The current ( I) across the junction has been found to decrease with the application of a magnetic field parallel to the plane of the CMS film clearly indicating positive junction magnetoresistance (JMR) of the heterostructure. When forward dc bias is applied to the heterostructure, the I- V characteristics are highly influenced on turning on the field B = 0.5 T at 78 K, and the forward current reduces abruptly (99.2% current reduction at 3 V) which is nearly equal to the order of the magnitude of the current observed in the reverse bias. Hence, our Co2MnSi/SiO2/p-Si heterostructure can perform in off ( I off)/on ( I on) states with the application of non-zero/zero magnetic field like a spin valve at low temperature (78 K).

  3. Spin physics and transport in narrow-gap III-V based heterostructures and epilayers

    CERN Document Server

    Rowe, A C H

    2000-01-01

    mixing of the first subband SdH series and a magneto-intersubband oscillation, the onset of which occurs when the Fermi energy is close to the bottom of the second subband. It is only at the lowest concentrations where the well asymmetry is minimal that beat patterns due to two narrowly split SdH series are observed. This splitting energy is found to be dependent on magnetic field, dropping from approx 4.8 meV at B = 0 T to approx 3.2 meV at B 1.3 T. In contrast, no beating is found in gated InAs/AISb wells at 4.2K over the largest concentration range yet reported in a single sample (4.8x10 sup 1 sup 1 cm sup - sup 2 < n < 2.4x10 sup 1 sup 2 cm sup - sup 2). The Heusler alloy NiMnSb is identified as a candidate for an electrical spin injector for InAs. A simple technique for the fabrication of bulk NiMnSb targets for laser ablation is detailed, and attempts at laser ablation of NiMnSb thin films are reported. Oxygen is identified as the major contaminant for the production of stoichiometric films. High ...

  4. Spin dynamics in GaAs and (110)-GaAs heterostructures; Spindynamik in GaAs und (110)-GaAs-Heterostrukturen

    Energy Technology Data Exchange (ETDEWEB)

    Oertel, Stefan

    2012-07-01

    This thesis investigates the spin dynamics in both bulk GaAs and (llO)GaAs heterostructures using time- and polarization-resolved photoluminescence spectroscopy. In bulk GaAs the spin relaxation t ime is measured for the first time in the high temperature regime from 280 K to 400 K and is compared to numerical calculations. The numerical calculations are based on the spin relaxation theory of the Dyakonov-Perel mechanism effected by momentum scattering with polar optical phonons and electron-electron scattering and are in good agreement with the experimental results. Measurements of the dependence on the electron density serve to determine the energy dependent proportional factor between the electron density and the effective electron-electron scattering time. Also in bulk GaAs the interaction between the electron spin system and the nuclear spin system is investigated. The measured electron Lande g-factor under the influence of the nuclear magnetic field is used as an indicator to monitor the temporal evolution of the nuclear magnetic field under sustained dynamic nuclear polarization. Measurements with polarization modulated excitation enable the determination of the relevant time scale at which dynamic nuclear polarization takes place. Furthermore, the temporal evolution of the measured electron Lande g-factor shows the complex interplay of the dynamic nuclear polarization, the nuclear spin diffusion and the nuclear spin relaxation. In symmetric (110)-GaAs quantum wells the dependence of the inplane anisotropy of the electron Lande g-factor on the quantum well thickness is determined experimentally. The measurements are in very good agreement with calculations based upon k . p-theory and reveal a maximum of the anisotropy at maximum carrier localization in the quantum well. The origin of the anisotropy that is not present in symmetric (001) quantum wells is qualitatively described by means of a simplified model based on fourth-order perturbation theory. A

  5. Spin texture on top of flux avalanches in Nb/Al 2 O 3 /Co thin film heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Lopes, R. F.; Carmo, D.; Colauto, F.; Ortiz, W. A.; de Andrade, A. M. H.; Johansen, T. H.; Baggio-Saitovitch, E.; Pureur, P.

    2017-01-07

    We report on magneto-optical imaging, magnetization, Hall effect, and magneto-resistance experiments in Nb/Al2O3/Co thin film heterostructures. The magneto-transport measurements were performed in samples where electrical contacts were placed on the Co layer. The magnetic field is applied perpendicularly to the plane of the film and gives rise to abrupt flux penetration of dendritic form. A magnetization texture is imprinted in the Co layer in perfect coincidence with these ramifications. The spin domains that mimic the vortex dendrites are stable upon the field removal. Moreover, the imprinted spin structure remains visible up to room temperature. In the region of the field-temperature diagram where flux instabilities are known to occur in bare Nb films, irregular jumps are observed in the magnetic hysteresis and large amplitude noise is detected in the magneto-resistance and Hall resistivity data when measured as a function of the field. Published by AIP Publishing.

  6. Thermoelectric performance of spin Seebeck effect in Fe3O4/Pt-based thin film heterostructures

    OpenAIRE

    Ramos, R.; Anadon, A.; Lucas, I.; Uchida, K.; Algarabel, P. A.; Morellon, L.; Aguirre, M. H.; Saitoh, E.; Ibarra, M. R.

    2016-01-01

    We report a systematic study on the thermoelectric performance of spin Seebeck devices based on Fe3O4/Pt junction systems. We explore two types of device geometries: a spin Hall thermopile and spin Seebeck multilayer structures. The spin Hall thermopile increases the sensitivity of the spin Seebeck effect, while the increase in the sample internal resistance has a detrimental effect on the output power. We found that the spin Seebeck multilayers can overcome this limitation since the multilay...

  7. Strain effects on the spin polarized electron gas in ABO3/SrTiO3 (A = Pr, Nd and B = Al, Ga) heterostructures

    KAUST Repository

    Nazir, Safdar

    2013-04-11

    The spin polarized two dimensional electron gas in the correlated ABO3/SrTiO3 (A = Pr, Nd and B = Al, Ga) heterostructures is investigated by ab-initio calculations using density functional theory. Structural relaxation shows a strong buckling at and near the TiO2 terminated n-type interface (IFs) due to significant TiO6 octahedral distortions. We find in all cases, metallic states in a very narrow region of the SrTiO3, in agreement with experimental results. We demonstrate that the interface magnetism strongly reacts to the magnitude of the lattice strain. The orbital occupations and, hence, the charge carrier density change systematically as a function of the lattice mismatch between the component materials.

  8. Thermoelectric performance of spin Seebeck effect in Fe3O4/Pt-based thin film heterostructures

    Directory of Open Access Journals (Sweden)

    R. Ramos

    2016-10-01

    Full Text Available We report a systematic study on the thermoelectric performance of spin Seebeck devices based on Fe3O4/Pt junction systems. We explore two types of device geometries: a spin Hall thermopile and spin Seebeck multilayer structures. The spin Hall thermopile increases the sensitivity of the spin Seebeck effect, while the increase in the sample internal resistance has a detrimental effect on the output power. We found that the spin Seebeck multilayers can overcome this limitation since the multilayers exhibit the enhancement of the thermoelectric voltage and the reduction of the internal resistance simultaneously, therefore resulting in significant power enhancement. This result demonstrates that the multilayer structures are useful for improving the thermoelectric performance of the spin Seebeck effect.

  9. Low-temperature Spin Spray Deposited Ferrite/piezoelectric Thin Film Magnetoelectric Heterostructures with Strong Magnetoelectric Coupling

    Science.gov (United States)

    2014-01-08

    dissipa- tion, which can be readily integrated in different integrated circuits. 1 Introduction Layered magnetoelectric (ME) heterostructures with two...single crystal, such as lead zirconate titanate, barium titanate, lead zinc nio- bate lead titanate (PZN-PT), lead magnesium niobate - lead titanate...negligible inter-diffusion between Fe3O4 and ZnO layers was obtained from the low- temperature deposition, which led to a tight interface bonding and strong

  10. Hf thickness dependence of spin-orbit torques in Hf/CoFeB/MgO heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Ramaswamy, Rajagopalan; Qiu, Xuepeng; Dutta, Tanmay; Pollard, Shawn David; Yang, Hyunsoo, E-mail: eleyang@nus.edu.sg [Department of Electrical and Computer Engineering, National University of Singapore, 117576 Singapore (Singapore)

    2016-05-16

    We have studied the spin-orbit torques in perpendicularly magnetized Hf/CoFeB/MgO system, by systematically varying the thickness of Hf underlayer. We have observed a sign change of effective fields between Hf thicknesses of 1.75 and 2 nm, indicating that competing mechanisms, such as the Rashba and spin Hall effects, contribute to spin-orbit torques in our system. For larger Hf thicknesses (>2 nm), both the components of spin-orbit torques arise predominantly from the bulk spin Hall effect. We have also confirmed these results using spin-orbit torque induced magnetization switching measurements. Our results could be helpful in designing Hf based SOT devices.

  11. Magnetoelectric coupling and spin-dependent tunneling in Fe/PbTiO{sub 3}/Fe multiferroic heterostructure with a Ni monolayer inserted at one interface

    Energy Technology Data Exchange (ETDEWEB)

    Dai, Jian-Qing, E-mail: djqkust@sina.com; Zhang, Hu; Song, Yu-Min [School of Materials Science and Engineering, Kunming University of Science and Technology, Kunming 650093 (China)

    2015-08-07

    We report on first-principles calculations of a Ni monolayer inserted at one interface in the epitaxial Fe/PbTiO{sub 3}/Fe multiferroic heterostructure, focusing on the magnetoelectric coupling and the spin-dependent transport properties. The results of magnetoelectric coupling calculations reveal an attractive approach to realize cumulative magnetoelectric effects in the ferromagnetic/ferroelectric/ferromagnetic superlattices. The underlying physics is attributed to the combinations of several different magnetoelectric coupling mechanisms such as interface bonding, spin-dependent screening, and different types of magnetic interactions. We also demonstrate that inserting a Ni monolayer at one interface in the Fe/PbTiO{sub 3}/Fe multiferroic tunnel junction is an efficient method to produce considerable tunneling electroresistance effect by modifying the tunnel potential barrier and the interfacial electronic structure. Furthermore, coexistence of tunneling magnetoresistance and tunneling electroresistance leads to the emergence of four distinct resistance states, which can be served as a multistate-storage device. The complicated influencing factors including bulk properties of the ferromagnetic electrodes, decay rates of the evanescent states in the tunnel barrier, and the specific interfacial electronic structure provide us promising opportunities to design novel multiferroic tunnel junctions with excellent performances.

  12. The compositional, structural, and magnetic properties of a Fe{sub 3}O{sub 4}/Ga{sub 2}O{sub 3}/GaN spin injecting hetero-structure grown by metal-organic chemical vapor deposition

    Energy Technology Data Exchange (ETDEWEB)

    Xu, Zhonghua; Huang, Shimin [Nanjing National Laboratory of Microstructures and School of Electronic Science and Engineering, Nanjing University, Nanjing 210023 (China); Tang, Kun, E-mail: ktang@nju.edu.cn [Nanjing National Laboratory of Microstructures and School of Electronic Science and Engineering, Nanjing University, Nanjing 210023 (China); Gu, Shulin, E-mail: slgu@nju.edu.cn [Nanjing National Laboratory of Microstructures and School of Electronic Science and Engineering, Nanjing University, Nanjing 210023 (China); Zhu, Shunming [Nanjing National Laboratory of Microstructures and School of Electronic Science and Engineering, Nanjing University, Nanjing 210023 (China); Ye, Jiandong [Nanjing National Laboratory of Microstructures and School of Electronic Science and Engineering, Nanjing University, Nanjing 210023 (China); Nanjing University Institute of Optoelectronics at Yangzhou, Yangzhou 225009 (China); Xu, Mingxiang [Department of Physics, Southeast University, Nanjing 210096 (China); Wang, Wei; Zheng, Youdou [Nanjing National Laboratory of Microstructures and School of Electronic Science and Engineering, Nanjing University, Nanjing 210023 (China)

    2016-12-01

    Highlights: • The Fe{sub 3}O{sub 4}/Ga{sub 2}O{sub 3}/GaN hetero-structure has been fabricated by MOCVD successfully. • The formation mechanism of different layers in sample was revealed in details. • The properties of the hetero-structure have been presented and discussed extensively. • The effect of Ga diffusion on the magnetic properties of Fe{sub 3}O{sub 4} film has been shown. - Abstract: In this article, the authors have designed and fabricated a Fe{sub 3}O{sub 4}/Ga{sub 2}O{sub 3}/GaN spin injecting hetero-structure by metal-organic chemical vapor deposition. The compositional, structural, and magnetic properties of the hetero-structure have been characterized and discussed. From the characterizations, the hetero-structure has been successfully grown generally. However, due to the unintentional diffusion of Ga ions from Ga{sub 2}O{sub 3}/GaN layers, the most part of the nominal Fe{sub 3}O{sub 4} layer is actually in the form of Ga{sub x}Fe{sub 3−x}O{sub 4} with gradually decreased x values from the Fe{sub 3}O{sub 4}/Ga{sub 2}O{sub 3} interface to the Fe{sub 3}O{sub 4} surface. Post-annealing process can further aggravate the diffusion. Due to the similar ionic radius of Ga and Fe, the structural configuration of the Ga{sub x}Fe{sub 3−x}O{sub 4} does not differ from that of pure Fe{sub 3}O{sub 4}. However, the ferromagnetism has been reduced with the incorporation of Ga into Fe{sub 3}O{sub 4}, which has been explained by the increased Yafet-Kittel angles in presence of considerable amount of Ga incorporation. A different behavior of the magnetoresistance has been found on the as-grown and annealed samples, which could be modelled and explained by the competition between the spin-dependent and spin-independent conduction channels. This work has provided detailed information on the interfacial properties of the Fe{sub 3}O{sub 4}/Ga{sub 2}O{sub 3}/GaN spin injecting hetero-structure, which is the solid basis for further improvement and application of

  13. Spin structure of exchange biased heterostructures. Fe/MnF{sub 2} and Fe/FeF{sub 2}

    Energy Technology Data Exchange (ETDEWEB)

    Sahoo, B.

    2006-12-18

    In this work, the {sup 57}Fe probe layer technique is used in order to investigate the depth- and temperature-dependent Fe-layer spin structure of exchange biased Fe/MnF{sub 2} and Fe/FeF{sub 2} (pseudo-twinned) antiferromagnetic (AFM) systems by conversion electron Moessbauer spectroscopy (CEMS) and nuclear resonant scattering (NRS) of synchrotron radiation. Two kinds of samples with a 10 A {sup 57}Fe probe layer directly at or 35 A away from the interface, labeled as interface and center sample, respectively, were studied in this work. The results obtained by CEMS for Fe/MnF{sub 2} suggests that, at 80 K, i.e., above T{sub N}=67 K of MnF{sub 2}, the remanent state Fe-layer spin structure of the two studied samples are slightly different due to their different microstructure. In the temperature range from 300 K to 80 K, the Fe-layer spin structure does not change just by zero-field cooling the sample in remanence. For Fe/FeF{sub 2}, a continuous non-monotonic change of the remanent-state Fe spin structure was observed by cooling from 300 K to 18 K. NRS of synchrotron radiation was used to investigate the temperature- and depth-dependent Fe-layer spin structure during magnetization reversal in pseudo-twinned Fe/MnF{sub 2}. A depthdependent Fe spin structure in an applied magnetic field (applied along the bisector of the twin domains) was observed at 10 K, where the Fe spins closer to the interface are not aligned along the field direction. The depth-dependence disappears at 150 K. (orig.)

  14. Electric-Field Modulation of Interface Magnetic Anisotropy and Spin Reorientation Transition in (Co/Pt)3/PMN-PT Heterostructure.

    Science.gov (United States)

    Sun, Ying; Ba, You; Chen, Aitian; He, Wei; Wang, Wenbo; Zheng, Xiaoli; Zou, Lvkuan; Zhang, Yijun; Yang, Qu; Yan, Lingjia; Feng, Ce; Zhang, Qinghua; Cai, Jianwang; Wu, Weida; Liu, Ming; Gu, Lin; Cheng, Zhaohua; Nan, Ce-Wen; Qiu, Ziqiang; Wu, Yizheng; Li, Jia; Zhao, Yonggang

    2017-03-29

    We report electric-field control of magnetism of (Co/Pt) 3 multilayers involving perpendicular magnetic anisotropy with different Co-layer thicknesses grown on Pb(Mg,Nb)O 3 -PbTiO 3 (PMN-PT) FE substrates. For the first time, electric-field control of the interface magnetic anisotropy, which results in the spin reorientation transition, was demonstrated. The electric-field-induced changes of the bulk and interface magnetic anisotropies can be understood by considering the strain-induced change of magnetoelastic energy and weakening of Pt 5d-Co 3d hybridization, respectively. We also demonstrate the role of competition between the applied magnetic field and the electric field in determining the magnetization of the sample with the coexistence phase. Our results demonstrate electric-field control of magnetism by harnessing the strain-mediated coupling in multiferroic heterostructures with perpendicular magnetic anisotropy and are helpful for electric-field modulations of Dzyaloshinskii-Moriya interaction and Rashba effect at interfaces to engineer new functionalities.

  15. Spin-flip-Raman studies of semimagnetic II-VI heterostructures; Spin-flip-Raman-Untersuchungen an semimagnetischen II-VI-Halbleiter-Quantentroegen und Volumenproben

    Energy Technology Data Exchange (ETDEWEB)

    Lentze, Michael

    2009-03-18

    In the present doctoral thesis, spin flip Raman studies of semimagnetic (Zn,Mn)Se samples were in the focus of interest. Quantum wells as well as bulk-like materials were investigated. The main goal was a better understanding of the exchange interaction behaviour of heavily n-doped semimagnetic samples. The influence of doping on the exchange interaction is of special relevance with regard to spintronics applications. Several series of high quality MBE-grown (Zn,Mn)Se-samples samples were available. (orig.)

  16. Nonequilibrium green function approach to elastic and inelastic spin-charge transport in topological insulator-based heterostructures and magnetic tunnel junctions

    Science.gov (United States)

    Mahfouzi, Farzad

    ferromagnet (FM). I show that this could be due to the existence of Rashba spin-orbit coupling (SOC) at the interface of the FM and insulator. Assuming that the measured signals are quantum mechanical effect where a solution to the time dependent Schrodinger equation is required, I use Keldysh Green function formalism to introduce a "multi-photon" approach which takes into account the effects of time-dependent term exactly up to scatterings from a finite number of photons. We then proceed to find the corresponding Green function numerically using a recursive method which allows us to increase the size of the system significantly. We also implement other approximations such as adiabatic and rotating frame approaches and compared them with our approach. In Chapter 4, I investigate the spin and charge pumping from a precessing magnetization attached to the edge of a 2-dimensional topological insulator (2DTI). We show that, in this system a huge spin current (or voltage signal if the FM covers only one edge) can be pumped for very small cone angles of the precessing FM (proportional to the intensity of the applied microwave). In Chapter 5 I present the third project in this field of research, where, I investigated the pumping from FM attached to a 3-dimensional TI. Spin-transfer torque: Presented in Chapter 6, in this work I investigate the torque induced by a flow of spin-polarized current into a FM and check the condition in which it can cause the magnetization to flip. Motivated by recent experimental developments in the field, here I consider systems with strong SOC such as TIs within a magnetic tunnel junction (MTJ) heterostructure. In the theoretical part I show the correct way (as opposed to the conventional approach used in some theoretical works which suffers from violation of the gauge invariance) to calculate linear-response torque to the external applied voltage and for the numerical calculation I adopted a parallelized adaptive integration algorithm in order to take

  17. Deterministic Switching of Perpendicular Magnetic Anisotropy by Voltage Control of Spin Reorientation Transition in (Co/Pt)3/Pb(Mg1/3Nb2/3)O3-PbTiO3Multiferroic Heterostructures.

    Science.gov (United States)

    Peng, Bin; Zhou, Ziyao; Nan, Tianxiang; Dong, Guohua; Feng, Mengmeng; Yang, Qu; Wang, Xinjun; Zhao, Shishun; Xian, Dan; Jiang, Zhuang-De; Ren, Wei; Ye, Zuo-Guang; Sun, Nian X; Liu, Ming

    2017-04-25

    One of the central challenges in realizing multiferroics-based magnetoelectric memories is to switch perpendicular magnetic anisotropy (PMA) with a control voltage. In this study, we demonstrate electrical flipping of magnetization between the out-of-plane and the in-plane directions in (Co/Pt) 3 /(011) Pb(Mg 1/3 Nb 2/3 )O 3 -PbTiO 3 multiferroic heterostructures through a voltage-controllable spin reorientation transition (SRT). The SRT onset temperature can be dramatically suppressed at least 200 K by applying an electric field, accompanied by a giant electric-field-induced effective magnetic anisotropy field (ΔH eff ) up to 1100 Oe at 100 K. In comparison with conventional strain-mediated magnetoelastic coupling that provides a ΔH eff of only 110 Oe, that enormous effective field is mainly related to the interface effect of electric field modification of spin-orbit coupling from Co/Pt interfacial hybridization via strain. Moreover, electric field control of SRT is also achieved at room temperature, resulting in a ΔH eff of nearly 550 Oe. In addition, ferroelastically nonvolatile switching of PMA has been demonstrated in this system. E-field control of PMA and SRT in multiferroic heterostructures not only provides a platform to study strain effect and interfacial effect on magnetic anisotropy of the ultrathin ferromagnetic films but also enables the realization of power efficient PMA magnetoelectric and spintronic devices.

  18. Unipolar Depression in Paroxysmal Schizophrenia

    Directory of Open Access Journals (Sweden)

    Alexander S. Bobrov

    2013-12-01

    Full Text Available Based on the current study, the clinical characteristics of unipolar depression in the clinical picture of schizophrenia with the paroxysmal type of disease course are presented. Given the concomitant depression with phobic symptoms, the following clinical variants are marked: depression with generalized social phobia and/or anthropophobia and depression with generalized pathological body sensations and hypochondriacal phobias. In other words, we are talking about a necessity to allocate a special type of schizophrenia with affective structure episodes and comorbid neurosis-like symptoms. Information on the basic treatment strategy of schizophrenia with depressive structure episodes and comorbid neurosis-like symptoms in everyday psychiatric practice is also provided.

  19. Recognition of Unipolar and Generalised Split Graphs

    Directory of Open Access Journals (Sweden)

    Colin McDiarmid

    2015-02-01

    Full Text Available A graph is unipolar if it can be partitioned into a clique and a disjoint union of cliques, and a graph is a generalised split graph if it or its complement is unipolar. A unipolar partition of a graph can be used to find efficiently the clique number, the stability number, the chromatic number, and to solve other problems that are hard for general graphs. We present an O(n2-time algorithm for recognition of n-vertex generalised split graphs, improving on previous O(n3-time algorithms.

  20. Psychological management of unipolar depression.

    Science.gov (United States)

    Lampe, L; Coulston, C M; Berk, L

    2013-01-01

    To be used in conjunction with 'Pharmacological management of unipolar depression' [Malhi et al. Acta Psychiatr Scand 2013;127(Suppl. 443):6-23] and 'Lifestyle management of unipolar depression' [Berk et al. Acta Psychiatr Scand 2013;127(Suppl. 443):38-54]. To provide clinically relevant recommendations for the use of psychological treatments in depression derived from a literature review. Medical databases including MEDLINE and PubMed were searched for pertinent literature, with an emphasis on recent publications. Structured psychological treatments such as cognitive behaviour therapy and interpersonal therapy (IPT) have a robust evidence base for efficacy in treating depression, even in severe cases of depression. However, they may not offer benefit as quickly as antidepressants, and maximal efficacy requires well-trained and experienced therapists. These therapies are effective across the lifespan and may be preferred where it is desired to avoid pharmacotherapy. In some instances, combination with pharmacotherapy may enhance outcome. Psychological therapy may have more enduring protective effects than medication and be effective in relapse prevention. Newer structured psychological therapies such as mindfulness-based cognitive therapy and acceptance and commitment therapy lack an extensive outcome literature, but the few published studies yielding positive outcomes suggest they should be considered options for treatment. Cognitive behaviour therapy and IPT can be effective in alleviating acute depression for all levels of severity and in maintaining improvement. Psychological treatments for depression have demonstrated efficacy across the lifespan and may present a preferred treatment option in some groups, for example, children and adolescents and women who are pregnant or postnatal. © 2013 John Wiley & Sons A/S. Published by Blackwell Publishing Ltd.

  1. Spin effects in high- and low-field magnetotransport experiments in semimagnetic Cd{sub 1-x}Mn{sub x}Te heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Betthausen, Christian

    2012-07-09

    Within the framework of this PhD we report on the very first observation of the fractional Quantum Hall Effect (FQHE) in both, a non-magnetic CdTe and a semimagnetic Cd{sub 1-x}Mn{sub x}Te quantum well device. To our knowledge, this constitutes the first demonstration of this effect in the II-VI material family. Furthermore, our results reveal that the formation of fractional Quantum Hall states is not inhibited by the presence of magnetic impurities in a quantum structure. The second part of this thesis addresses an alternative route to realize efficient spin transistor action. Typically, spin transistor designs relying on spin-orbit interaction principally suffer from low signal levels due to limitations in spin injection efficiency and fast spin decay. Here we present an approach to realize spin transistor action in systems where spin information is protected by propagating it adiabatically. This is achieved by inducing tunable diabatic Landau-Zener transitions that lead to a backscattering of spins and hence allow controlling the transmission of spin-polarized charge carriers through the device, i.e. switching between 'on' and 'off' states. We demonstrate the validity of our approach in a Cd{sub 1-x}Mn{sub x}Te diluted magnetic semiconductor quantum well structure where efficient spin transport is observed over device distances of 50 {mu}m. In contrast to other spin transistor designs we find that our concept is exceptionally tolerant against disorder.

  2. Quantum interference and spin-orbit effects in the heterostructure with the 2D hole gas in the Si sub 0 sub . sub 2 Ge sub 0 sub . 8 quantum well

    CERN Document Server

    Andrievskij, V V; Komnik, Y F; Mironov, M; Mironov, O A; Whall, T E

    2003-01-01

    The magnetic field (approx 110 kOe)dependences of resistance of the Si sub 0 sub . sub 7 Ge sub 0 sub . sub 3 /Si sub 0 sub . sub 2 Ge sub 0 sub . sub 8 /Si sub 0 sub . sub 7 Ge sub 0 sub . sub 3 heterostructure with a 2D hole gas in the Si sub 0 sub . sub 2 Ge sub 0 sub . sub 8 quantum well were measured at T = 0.335-10 K with varying current between 100 nA and 50 mA. It was found that in high magnetic fields there occurred Shubnikov-de-Haas oscillations, while in weak fields (H<= kOe) a positive magnetoresistance transforming than in a negative one was observed. This peculiarity is due to the effects of weak localization of 2D charge carriers with very close spin-orbit and inelastic scattering time,tau sub s sub o and tau subphi, respectively. This suggests that the spin states are splitted in response to the perturbing potential associated with the generation of a two-dimensional potential well (Rashba mechanism). The analysis of the effects of weak localization yields the characteristic relaxation time...

  3. Magnetic Nanostructures Spin Dynamics and Spin Transport

    CERN Document Server

    Farle, Michael

    2013-01-01

    Nanomagnetism and spintronics is a rapidly expanding and increasingly important field of research with many applications already on the market and many more to be expected in the near future. This field started in the mid-1980s with the discovery of the GMR effect, recently awarded with the Nobel prize to Albert Fert and Peter Grünberg. The present volume covers the most important and most timely aspects of magnetic heterostructures, including spin torque effects, spin injection, spin transport, spin fluctuations, proximity effects, and electrical control of spin valves. The chapters are written by internationally recognized experts in their respective fields and provide an overview of the latest status.

  4. Hole-spin dynamics in p-doped GaAs/AlGaAs heterostructures; Lochspindynamik in p-dotierten GaAs/AlGaAs-Heterostrukturen

    Energy Technology Data Exchange (ETDEWEB)

    Kugler, Michael

    2012-11-15

    This work investigates the spin dynamics of holes in p-doped GaAs/AlGaAs quantum wells (QW) at low temperatures. To examine the energetic structure of the used samples, PL and PLE-spectroscopy were employed. Time resolved Kerr and Faraday-Rotation (TRKR/FR) and 'Resonant Spin Amplification' (RSA) were used to analyse the spin dynamics. First, the signal formation in TRKR/FR and RSA experiments is discussed taking into account the interconnected charge carrier dynamics and spin dynamics of electrons and holes. An excitation energy dependent sign change of the Kerr signal amplitude could be observed, whose energetic position corresponds to an absorption maximum in PLE experiments. This behavior could be explained by an energy dependent splitting of the spin niveaus, which leads to an energy dependence of the Faraday and Kerr signal. Furthermore, two initialization processes were investigated, which could be used to transfer optically generated spin information into the resident hole spin system. This could be achieved by either applying a magnetic field, or by rapid dephasing of hole spins immediately after excitation. Changes in excitation energy, excitation density or temperature could be used to influence the fast dephasing processes and therefore the initial ratio of hole to electron spins. The complex, interconnected charge carrier and spin dynamics of electrons and holes could be accurately reproduced using a rate equation model. This allowed for the extraction of physically relevant parameters like spin lifetimes and g-factors from RSA and TRKR/FR data. An analytical model that was developed at the Wroclaw University of Technology delivered matching results. In the second part of the experimental work, the dependence of the hole spin lifetime and the hole g-factor on various parameters was analysed. Here, the RSA method could for the first time be applied to two-dimensional hole systems, allowing for new insights into the regime of long lived hole

  5. Spin-polarized electron gas in Co2MSi/SrTiO3(M= Ti, V, Cr, Mn, and Fe) heterostructures

    KAUST Repository

    Nazir, S.

    2016-06-08

    Spin-polarized density functional theory is used to study the TiO2 terminated interfaces between the magnetic Heusler alloys Co2Si (M = Ti, V, Cr, Mn, and Fe) and the non-polar band insulator SrTiO3. The structural relaxation at the interface turns out to depend systematically on the lattice mis- match. Charge transfer from the Heusler alloys (mainly the M 3d orbitals) to the Ti dxy orbitals of the TiO2 interface layer is found to gradually grow from M = Ti to Fe, resulting in an electron gas with increasing density of spin-polarized charge carriers. (© 2016 WILEY-VCH Verlag GmbH &Co. KGaA, Weinheim). © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

  6. Scaling down the two-dimensional electron gas spin resonance (ESR) phenomena in GaAs/AlGaAs heterostructures to sub-micron samples

    Science.gov (United States)

    Bandaru, Prabhakar; Yablonovitch, Eli; Jiang, Hong-Wen

    2002-03-01

    Electron Spin Resonance (ESR) has been proposed as a technique for achieving single electron and subsequently single spin control, important for the emerging fields of spintronics and quantum computing. In this paper, we report on ESR in the quantum Hall regime, of sub-micron structures containing a few hundred electrons. These phenomena are contrasted with ESR phenomena in structures containing 10^7 - 10^9 electrons, which have been performed so far (Reference 1). There are several novel features observed in the ESR of small structures, such as a very large decrease of resistance and shift in the quantum Hall minima to lower magnetic fields after the resonance. These imply a reduction in the number of electrons and could result from the greater influence of the surface and impurity potential fluctuations intrinsic to a small sample. The ESR peak intensity is hypothesized to result from the transfer of electrons from the localized states to the extended states. References: 1.H.W.Jiang and E. Yablonovitch, Phys. Rev.B., 64, R041307, (2001) 2.M.Dobers, K.v. Klitzing and G. Weimann,Phys. Rev. B, 38, 5453, (1988).

  7. Motor imagery in unipolar major depression

    Directory of Open Access Journals (Sweden)

    Djamila eBennabi

    2014-12-01

    Full Text Available Background: Motor imagery is a potential tool to investigate action representation, as it can provide insights into the processes of action planning and preparation. Recent studies suggest that depressed patients present specific impairment in mental rotation. The present study was designed to investigate the influence of unipolar depression on motor imagery ability.Methods: Fourteen right-handed patients meeting DSM-IV criteria for unipolar depression were compared to fourteen matched healthy controls. Imagery ability was accessed by the timing correspondence between executed and imagined movements during a pointing task, involving strong spatiotemporal constraints (speed/accuracy trade off paradigm.Results: Compared to controls, depressed patients showed marked motor slowing on both actual and imagined movements. Furthermore, we observed greater temporal discrepancies between actual and mental movements in depressed patients than in healthy controls. Lastly, depressed patients modulated, to some extent, mental movement durations according to the difficulty of the task, but this modulation was not as strong as that of healthy subjects.Conclusion: These results suggest that unipolar depression significantly affects the higher stages of action planning and point out a selective decline of motor prediction.

  8. Anisotropic magnetoresistance in topological insulator Bi1.5Sb0.5Te1.8Se1.2/CoFe heterostructures

    National Research Council Canada - National Science Library

    Xia, B; Ren, P; Sulaev, Azat; Li, Z. P; Liu, P; Dong, Z. L; Wang, L

    2012-01-01

    ... Bi1.5Sb0.5Te1.8Se1.2/CoFe heterostructures. To explain the novel effect, we propose that the Bi1.5Sb0.5Te1.8Se1.2/CoFe heterostructure forms a spin-valve or Giant magnetoresistance device due to spin-momentum locking...

  9. Pre-Earthquake Unipolar Electromagnetic Pulses

    Science.gov (United States)

    Scoville, J.; Freund, F.

    2013-12-01

    Transient ultralow frequency (ULF) electromagnetic (EM) emissions have been reported to occur before earthquakes [1,2]. They suggest powerful transient electric currents flowing deep in the crust [3,4]. Prior to the M=5.4 Alum Rock earthquake of Oct. 21, 2007 in California a QuakeFinder triaxial search-coil magnetometer located about 2 km from the epicenter recorded unusual unipolar pulses with the approximate shape of a half-cycle of a sine wave, reaching amplitudes up to 30 nT. The number of these unipolar pulses increased as the day of the earthquake approached. These pulses clearly originated around the hypocenter. The same pulses have since been recorded prior to several medium to moderate earthquakes in Peru, where they have been used to triangulate the location of the impending earthquakes [5]. To understand the mechanism of the unipolar pulses, we first have to address the question how single current pulses can be generated deep in the Earth's crust. Key to this question appears to be the break-up of peroxy defects in the rocks in the hypocenter as a result of the increase in tectonic stresses prior to an earthquake. We investigate the mechanism of the unipolar pulses by coupling the drift-diffusion model of semiconductor theory to Maxwell's equations, thereby producing a model describing the rock volume that generates the pulses in terms of electromagnetism and semiconductor physics. The system of equations is then solved numerically to explore the electromagnetic radiation associated with drift-diffusion currents of electron-hole pairs. [1] Sharma, A. K., P. A. V., and R. N. Haridas (2011), Investigation of ULF magnetic anomaly before moderate earthquakes, Exploration Geophysics 43, 36-46. [2] Hayakawa, M., Y. Hobara, K. Ohta, and K. Hattori (2011), The ultra-low-frequency magnetic disturbances associated with earthquakes, Earthquake Science, 24, 523-534. [3] Bortnik, J., T. E. Bleier, C. Dunson, and F. Freund (2010), Estimating the seismotelluric current

  10. Premorbid intelligence and educational level in bipolar and unipolar disorders

    DEFF Research Database (Denmark)

    Sørensen, Holger Jelling; Sæbye, Ditte; Urfer-Parnas, Annick

    2012-01-01

    Registry-based studies have found no or weak associations between premorbid intelligence and the broad entity of affective spectrum disorder, but none of the studies compared bipolar/unipolar subgroups.......Registry-based studies have found no or weak associations between premorbid intelligence and the broad entity of affective spectrum disorder, but none of the studies compared bipolar/unipolar subgroups....

  11. [Differences in Subjective Experience Between Unipolar and Bipolar Depression].

    Science.gov (United States)

    Fierro, Marco; Bustos, Andrés; Molina, Carlos

    2016-01-01

    It is important to make distinction between bipolar and unipolar depression because treatment and prognosis are different. Since the diagnosis of the two conditions is purely clinical, find symptomatic differences is useful. Find differences in subjective experience (first person) between unipolar and bipolar depression. Phenomenological-oriented qualitative exploratory study of 12 patients (7 with bipolar depression and 5 with unipolar depression, 3 men and 9 women). We used a semi-structured interview based on Examination of Anomalous Self-Experience (EASE). The predominant mood in bipolar depression is emotional dampening, in unipolar is sadness. The bodily experience in bipolar is of a heavy, tired body; an element that inserts between the desires of acting and performing actions and becomes an obstacle to the movement. In unipolar is of a body that feels more comfortable with the stillness than activity, like laziness of everyday life. Cognition and the stream of consciousness: in bipolar depression, compared with unipolar, thinking is slower, as if to overcome obstacles in their course. There are more difficult to understand what is heard or read. Future perspective: in bipolar depression, hopelessness is stronger and broader than in unipolar, as if the very possibility of hope was lost. Qualitative differences in predominant mood, bodily experience, cognition and future perspective were found between bipolar and unipolar depression. Copyright © 2015 Asociación Colombiana de Psiquiatría. Publicado por Elsevier España. All rights reserved.

  12. Mortality and life expectancy in persons with severe unipolar depression

    DEFF Research Database (Denmark)

    Laursen, Thomas Munk; Musliner, Katherine L; Benros, Michael E

    2016-01-01

    rate ratios (MRRs) and life expectancy in persons with unipolar depression were calculated using survival analysis techniques. RESULTS: The overall MRR was 2.07 (95% Confidence Interval (CI): 2.05-2.09) in people with a previous unipolar depression diagnosis compared to the general Danish population...

  13. Heterostructures and quantum devices

    CERN Document Server

    Einspruch, Norman G

    1994-01-01

    Heterostructure and quantum-mechanical devices promise significant improvement in the performance of electronic and optoelectronic integrated circuits (ICs). Though these devices are the subject of a vigorous research effort, the current literature is often either highly technical or narrowly focused. This book presents heterostructure and quantum devices to the nonspecialist, especially electrical engineers working with high-performance semiconductor devices. It focuses on a broad base of technical applications using semiconductor physics theory to develop the next generation of electrical en

  14. Theory of unidirectional magnetoresistance in magnetic heterostructures

    Science.gov (United States)

    Zhang, Steven S.-L.; Vignale, Giovanni

    2017-09-01

    We present a general drift-diffusion theory beyond linear response to explain the unidirectional magnetoresistance (UMR) observed in recent experiments in various magnetic heterostructures. In general, such nonlinear magnetoresistance may originate from the concerted action of current-induced spin accumulation and spin asymmetry in electron mobility. As a case study, we calculate the UMR in a bilayer system consisting of a heavy-metal (HM) and a ferromagnetic metal (FM), where the spin accumulation is induced via the spin Hall effect in the bulk of the HM layer. Our previous formulation [cf. PRB 94, 140411(R) (2016)] is generalized to include the interface resistance and spin memory loss, which allows us to analyze in details their effects on the UMR. We found that the UMR turns out to be independent of the spin asymmetry of the interfacial resistance, at variance with the linear giant-magnetoresistance (GMR) effect. A linear relation between the UMR and the conductivity-spin asymmetry is revealed, which provides an alternative way to control the sign and magnitude of the UMR and hence may serve as an experimental signature of our proposed mechanism.

  15. Screening for cognitive dysfunction in unipolar depression

    DEFF Research Database (Denmark)

    Ott, Caroline Vintergaard; Bjertrup, Anne Juul; Jensen, Johan Høy

    2016-01-01

    with the executive skills domain only (r =-0.3, p=0.05). LIMITATIONS: A modest sample size. CONCLUSIONS: The SCIP-D and COBRA are valid measures of objective and subjective cognitive impairment, respectively, and should ideally be implemented together in the screening for cognitive dysfunction in UD.......BACKGROUND: Persistent cognitive dysfunction in unipolar depression (UD) contributes to socio-occupational impairment, but there are no feasible methods to screen for and monitor cognitive dysfunction in this patient group. The present study investigated the validity of two new instruments...... to screen for cognitive dysfunction in UD, and their associations with socio-occupational capacity. METHOD: Participants (n=53) with UD in partial or full remission and healthy control persons (n=103) were assessed with two new screening instruments, the Danish translations of the Screen for Cognitive...

  16. Electric field control of magnetism in multiferroic heterostructures.

    Science.gov (United States)

    Vaz, C A F

    2012-08-22

    We review the recent developments in the electric field control of magnetism in multiferroic heterostructures, which consist of heterogeneous materials systems where a magnetoelectric coupling is engineered between magnetic and ferroelectric components. The magnetoelectric coupling in these composite systems is interfacial in origin, and can arise from elastic strain, charge, and exchange bias interactions, with different characteristic responses and functionalities. Moreover, charge transport phenomena in multiferroic heterostructures, where both magnetic and ferroelectric order parameters are used to control charge transport, suggest new possibilities to control the conduction paths of the electron spin, with potential for device applications.

  17. Cognitive deficits in the remitted state of unipolar depressive disorder

    DEFF Research Database (Denmark)

    Hasselbalch, Jacob; Knorr, Ulla; Hasselbalch, Steen Gregers

    2012-01-01

    Patients with unipolar depressive disorder may present with cognitive deficits in the remitted state, and the aim of the present study was to investigate whether cognitive deficits within specific cognitive domains are present....

  18. Myers Briggs Type indicator personality profiles in unipolar depressed patients.

    Science.gov (United States)

    Janowsky, David S; Hong, Elliot; Morter, Shirley; Howe, Laura

    2002-10-01

    The current study was designed to compare the distribution of Myers Briggs Type Indicator (MBTI) personality types in patients with Unipolar Depression compared to normative data. The MBTI divides individuals into four dichotomous types: Extroverted and Introverted, Sensing and Intuitive, Thinking and Feeling, and Judging and Perceiving. This yields eight single-factor and sixteen four-factor types. One-hundred-thirty Unipolar Depressed patients were administered the MBTI-Form F. Unipolar Depressed patients were significantly more often Introverted, Sensing, Feeling, and Perceiving single-factor types respectively, and Introverted-Sensing-Feeling-Perceiving, and Introverted-Intuitive-Feeling-Perceiving four-factor types. The male Introverted-Sensing-Feeling-Perceiving four-factor type was the most dramatically over-represented. The MBTI effectively discriminates a patient group with Unipolar Depression from a normative population.

  19. Sleep patterns and the risk for unipolar depression: a review

    OpenAIRE

    Wiebe ST; Cassoff J; Gruber R

    2012-01-01

    Sabrina T Wiebe, Jamie Cassoff, Reut GruberAttention, Behavior and Sleep Laboratory, Douglas Mental Health University Institute, Montréal; McGill University, Montréal, Quebec, CanadaAbstract: Psychological disorders, particularly mood disorders, such as unipolar depression, are often accompanied by comorbid sleep disturbances, such as insomnia, restless sleep, and restricted sleep duration. The nature of the relationship between unipolar depression and these sleep distur...

  20. Differences between bipolar and unipolar depression on Rorschach testing.

    Science.gov (United States)

    Kimura, Hiromi; Osaki, Akemi; Kawashima, Rui; Inoue, Takeshi; Nakagawa, Shin; Suzuki, Katsuji; Asakura, Satoshi; Tanaka, Teruaki; Kitaichi, Yuji; Masui, Takuya; Kitagawa, Nobuki; Kako, Yuki; Abekawa, Tomohiro; Kusumi, Ichiro; Yamanaka, Hiroyoshi; Denda, Kenzo; Koyama, Tsukasa

    2013-01-01

    The bipolar-unipolar distinction in patients with a major depressive episode is the most important issue related to the diagnosis and treatment of mood disorders, but remains unresolved. This study was undertaken to compare bipolar and unipolar depression on Rorschach testing using the Comprehensive System with reference to healthy Japanese controls. Patients with bipolar or unipolar depression who had undergone the Rorschach test for routine clinical purposes were followed up naturalistically for a long period. Based on diagnostic confirmation after long-term follow-up, scores on this test for patients with bipolar and unipolar depression were compared with those published elsewhere for healthy Japanese controls. The bipolar depression group showed significantly higher scores or positive findings in five variables of the Rorschach test, ie, WSum6, DR2 > 0, (CF + C) > FC + 2, PureC > 1, and Populars > 7, as assessed using the Comprehensive System, than did the unipolar depression group and healthy controls. These scores did not differ between the unipolar depression and control groups. The results of this study show thought disorder or cognitive slippage and marked laxness in modulating emotion in bipolar depression, indicating the psychopathological characteristics of bipolar disorder.

  1. Black phosphorene/monolayer transition-metal dichalcogenides as two dimensional van der Waals heterostructures: a first-principles study.

    Science.gov (United States)

    You, Baiqing; Wang, Xiaocha; Zheng, Zhida; Mi, Wenbo

    2016-03-14

    The electronic structure of black phosphorene (BP)/monolayer 1H-XT2 (X = Mo, W; T = S, Se, Te) two dimensional (2D) van der Waals heterostructures have been calculated by the first-principles method. It is found that the electronic band structures of both BP and XT2 are preserved in the combined van der Waals heterostructures. The WSe2/BP van der Waals heterostructure demonstrates a type-I band alignment, but the MoS2/BP, MoSe2/BP, MoTe2/BP, WS2/BP and WTe2/BP van der Waals heterostructures demonstrate a type-II band alignment. In particular, the n-type XT2/p-type BP van der Waals heterostructures can be applied in p-n diode and logical devices. Strong spin splitting appears in all of the heterostructures when considering the spin orbital coupling. Our results play a significant role in the prediction of novel 2D van der Waals heterostructures that have potential applications in spin-filter devices, spin field effect transistors, optoelectronic devices, etc.

  2. Personality traits and maladaptivity: Unipolarity versus bipolarity.

    Science.gov (United States)

    Williams, Trevor F; Simms, Leonard J

    2017-11-24

    Dimensional personality trait models have gained favor as an alternative to categorical personality disorder (PD) diagnosis; however, debate persists regarding whether these traits should be conceptualized as maladaptive at both extremes (i.e., maladaptively bipolar) or just one trait pole (i.e., unipolar). To inform the debate on maladaptive bipolarity, linear and nonlinear relations between personality traits and dysfunction were examined in a large psychiatric patient sample (N = 365). Participants self-reported on normal-range and pathological personality domains, life satisfaction, specific interpersonal problems, and broad psychosocial functioning. In addition, participants were interviewed regarding specific psychiatric symptoms and broad psychosocial functioning. All traits related moderately to strongly with at least one dysfunction variable. All traits were predominantly correlated with dysfunction at one pole; however, several small linear relations provided some evidence for maladaptively high Extraversion and Agreeableness. None of the significant nonlinear effects provided clear evidence for maladaptivity at both ends of any trait. Taken together, these results suggest that broad personality traits are predominantly maladaptive at one extreme; however, in limited cases, the opposite extreme may also be maladaptive. © 2017 Wiley Periodicals, Inc.

  3. Peculiar Black-Hole Unipolar Induction

    Science.gov (United States)

    Okamoto, Isao

    2012-06-01

    It is argued that a posteriori without conflicting with the dubbed no-hair theorem, a Kerr black hole acquires its own proper magnetosphere in the steady eigen-state. The angular frequency of field lines, ΩF, given as the eigenvalue in terms of the hole's angular frequency, ΩH , couples with the frame-dragging angular frequency, ω, to create an inner general-relativistic domain of ΩH > ω > ΩF, in which the gradient of the electric potential is, when viewed by the fiducial observers (FIDOs), reversed in direction from that in the outer quasi-classical domain of ΩF > ω > 0. The field lines are pinned down in the plasma source at the interface between the two domains (upper null surface SN), from which pair-particles well up, charge-separated into the ingoing and outgoing winds. The EMFs due to unipolar induction operate to drive the surface currents, following Ohm's law, on the resistive membranes terminating the force-free domains (say, SffH and Sff∞), to exert the surface torques onto the respective membranes, thereby extracting angular momentum from the hole and transferring to the domain of astrophysical loads.

  4. From Two to One: Unipolar Sexual Reproduction

    Science.gov (United States)

    Sun, Sheng; Heitman, Joseph

    2015-01-01

    While sexual reproduction is universal in eukaryotes, and shares conserved core features, the specific aspects of sexual reproduction can differ dramatically from species to species. This is also true in Fungi. Among fungal species, mating determination can vary from tetrapolar with more than a thousand different mating types, to bipolar with only two opposite mating types, and finally to unipolar without the need of a compatible mating partner for sexual reproduction. Cryptococcus neoformans is a human pathogenic fungus that belongs to the Basidiomycota. While C. neoformans has a well-defined bipolar mating system with two opposite mating types, MATa and MATα, it can also undergo homothallic unisexual reproduction from one single cell or between two cells of the same mating type. Recently, it was shown that, as in a-α bisexual reproduction, meiosis is also involved in α-α unisexual reproduction in C. neoformans. Briefly, recombination frequencies, the number of crossovers along chromosomes, as well as frequencies at which aneuploid and diploid progeny are produced, are all comparable between a-α bisexual and α-α unisexual reproduction. The plasticity observed in C. neoformans sexual reproduction highlights the extensive diversity in mating type determination, mating recognition, as well as modes of sexual reproduction across fungal species. PMID:26744600

  5. Modelo experimental de un motor unipolar

    Directory of Open Access Journals (Sweden)

    Luz Karine Sandoval

    2010-01-01

    Full Text Available Se describe la caracterización experimental de un prototipo de motor unipolar con el objeto de validar su modelo matemático. Este tipo de motor es bastante controversial a la hora de pretender explicar su modelo y fundamento de operación. Ha existido por cerca de casi dos siglos y aún persiste su misteriosa forma de funcionamiento; parece eludir cualquier explicación convencional a la luz de las ecuaciones de Maxwell. Es un dispositivo que genera una fuerza electromotriz (fem, aunque el flujo magnético que atraviesa el circuito no varía con el tiempo. El prototipo construido mostró la validez del modelo, esto es, una resistencia eléctrica y una fuente de tensión, puesto que al medir la velocidad angular alcanzada durante un intervalo de tiempo, se observó su crecimiento exponencial. La función de transferencia del motor es de primer orden, justo como se esperaba, dado que carece de elementos como bobinas o capacitores; sin embargo, tarda de treinta a cuarenta segundos en alcanzar su estado estable. Esto se debe, según el modelo planteado, a la resistencia eléctrica interna de este dispositivo.

  6. Interface-engineered oxygen octahedral coupling in manganite heterostructures

    Science.gov (United States)

    Huijben, M.; Koster, G.; Liao, Z. L.; Rijnders, G.

    2017-12-01

    Control of the oxygen octahedral coupling (OOC) provides a large degree of freedom to manipulate physical phenomena in complex oxide heterostructures. Recently, local tuning of the tilt angle has been found to control the magnetic anisotropy in ultrathin films of manganites and ruthenates, while symmetry control can manipulate the metal insulator transition in nickelate thin films. The required connectivity of the octahedra across the heterostructure interface enforces a geometric constraint to the 3-dimensional octahedral network in epitaxial films. Such geometric constraint will either change the tilt angle to retain the connectivity of the corner shared oxygen octahedral network or guide the formation of a specific symmetry throughout the epitaxial film. Here, we will discuss the control of OOC in manganite heterostructures by interface-engineering. OOC driven magnetic and transport anisotropies have been realized in LSMO/NGO heterostructures. Competition between the interfacial OOC and the strain further away from the interface leads to a thickness driven sharp transition of the anisotropic properties. Furthermore, octahedral relaxation leading to a change of p-d hybridization driven by interfacial OOC appears to be the strongest factor in thickness related variations of magnetic and transport properties in epitaxial LSMO films on NGO substrates. The results unequivocally link the atomic structure near the interfaces to the macroscopic properties. The strong correlation between a controllable oxygen network and the functionalities will have significant impact on both fundamental research and technological application of correlated perovskite heterostructures. By controlling the interfacial OOC, it is possible to pattern in 3 dimensions the magnetization to achieve non-collinear magnetization in both in-plane and out of plane directions, thus making the heterostructures promising for application in orthogonal spin transfer devices, spin oscillators, and low

  7. Treatment of Femoral Neck Fractures: Unipolar Versus Bipolar Hemiarthroplasty

    Directory of Open Access Journals (Sweden)

    Somashekar

    2013-07-01

    Full Text Available BACKGROUND AND OBJECTIVE: Intracapsular femoral neck fractures are common in the elderly population. To avoid the poor outcome of internal fixation and for early mobilization, hemiarthroplasty is performed. However, there is inadequate evidence to support the choice between unipolar or bipolar hemiarthroplasty. The aim of this study was to compare the outcome of unipolar with the bipolar prosthesis in geriatric patients. METHODS: Forty-one patients above 60 years of age and an acute displaced fracture of the femoral neck were randomly allocated to treatment by either unipolar or bipolar hemiarthroplasty, in the Department of Orthopaedics, between September 2009 and October 2012. Functional outcome was assessed and compared using Harris hip score and radiological parameters with a follow-up of one year. RESULTS: The two groups of patients with mean age of 67.3 in bipolar group and 75.6 in unipolar group did not differ in their pre-injury characteristics and perioperative parameters. The mean Harris hip score in bipolar and unipolar groups was 86.18±12.18 and 79.79±15.55, respectively (p=0.183; range of motion was 210.63±28.39 and 181.58±37(p=0.015 with bipolar and unipolar groups, respectively. Functional activities were better in the bipolar group. Complications like painful hip, posterior dislocation, periprosthetic fracture and acetabular erosion were encountered in unipolar prostheses. CONCLUSION: The use of bipolar endoprosthesis in the management of displaced femoral neck fractures in the elderly was associated with better mean Harris hip score and incidence of complications was limited. Hence, bipolar would be a better option in elderly patients with fracture neck of femur.

  8. Differences between bipolar and unipolar depression on Rorschach testing

    Directory of Open Access Journals (Sweden)

    Kimura H

    2013-05-01

    Full Text Available Hiromi Kimura, Akemi Osaki, Rui Kawashima, Takeshi Inoue, Shin Nakagawa, Katsuji Suzuki, Satoshi Asakura, Teruaki Tanaka, Yuji Kitaichi, Takuya Masui, Nobuki Kitagawa, Yuki Kako, Tomohiro Abekawa, Ichiro Kusumi, Hiroyoshi Yamanaka, Kenzo Denda, Tsukasa KoyamaDepartment of Psychiatry, Hokkaido University Graduate School of Medicine, Kita-ku, Sapporo, JapanBackground: The bipolar-unipolar distinction in patients with a major depressive episode is the most important issue related to the diagnosis and treatment of mood disorders, but remains unresolved. This study was undertaken to compare bipolar and unipolar depression on Rorschach testing using the Comprehensive System with reference to healthy Japanese controls.Methods: Patients with bipolar or unipolar depression who had undergone the Rorschach test for routine clinical purposes were followed up naturalistically for a long period. Based on diagnostic confirmation after long-term follow-up, scores on this test for patients with bipolar and unipolar depression were compared with those published elsewhere for healthy Japanese controls.Results: The bipolar depression group showed significantly higher scores or positive findings in five variables of the Rorschach test, ie, WSum6, DR2 > 0, (CF + C > FC + 2, PureC > 1, and Populars > 7, as assessed using the Comprehensive System, than did the unipolar depression group and healthy controls. These scores did not differ between the unipolar depression and control groups.Conclusion: The results of this study show thought disorder or cognitive slippage and marked laxness in modulating emotion in bipolar depression, indicating the psychopathological characteristics of bipolar disorder.Keywords: bipolar depression, bipolar disorder, Rorschach test, thought disorder, unipolar depression

  9. Quantum spin Hall phase in multilayer graphene

    OpenAIRE

    García-Martínez, N. A.; Lado, Jose L.; Fernández Rossier, Joaquín

    2015-01-01

    The so-called quantum spin Hall phase is a topologically nontrivial insulating phase that is predicted to appear in graphene and graphenelike systems. In this paper we address the question of whether this topological property persists in multilayered systems. We consider two situations: purely multilayer graphene and heterostructures where graphene is encapsulated by trivial insulators with a strong spin-orbit coupling. We use a four-orbital tight-binding model that includes full atomic spin-...

  10. Anomalous subjective experiences in schizophrenia, bipolar disorder, and unipolar depression.

    Science.gov (United States)

    Kim, Jong-Hoon; Lee, Ju-Hee; Lee, Jinyoung

    2013-07-01

    The purpose of the present study was to compare anomalous subjective experiences in patients with schizophrenia, bipolar disorder, and unipolar depression, in order to elucidate differences in subjective experiences and examine their potential clinical correlates in schizophrenia and mood disorders. The subjective experiences of 78 outpatients with schizophrenia (n=32), bipolar disorder (n=24) and unipolar depression (n=22), and 32 healthy controls were comprehensively assessed using the Frankfurt Complaint Questionnaire (FCQ). The FCQ total score was significantly higher in the schizophrenia and depression groups than in the healthy control group. There were no significant differences in the FCQ total or subscale scores among the schizophrenia, unipolar depression, and bipolar disorder groups. In the schizophrenia group, the Positive and Negative Syndrome Scale negative factor score was a significant negative predictor of the severity of subjective experiences assessed by the FCQ total score. Disruption of subjective experiences in patients with unipolar depression was associated with greater severity of depressive symptoms and younger age. In the bipolar disorder group, women reported more disruptions in subjective experience. Anomalous subjective experiences measured by the FCQ are not specific to schizophrenia, and the severity of these experiences in unipolar depression is substantially high. The finding of a dissimilar pattern of predictors of subjective experiences across different diagnostic groups suggests the complexity and variety of factors contributing to anomalous subjective experiences in schizophrenia and mood disorders. Copyright © 2013 Elsevier Inc. All rights reserved.

  11. Early maladaptive schemas in patients with bipolar and unipolar disorder.

    Science.gov (United States)

    Özdin, Selçuk; Sarisoy, Gökhan; Şahin, Ahmet Rıfat; Arik, Ali Cezmi; Özyıldız Güz, Hatice; Böke, Ömer; Karabekiroğlu, Aytül

    2018-06-01

    The aim of our study is to determine the difference between the bipolar disorder, unipolar disorder and control groups in terms of maladaptive schemes and childhood trauma. Two groups of patients under monitoring with a diagnosis of bipolar or unipolar disorder and one group of healthy controls were enrolled in this study. Each group consisted of 60 subjects. The Young Mania Rating Scale and Beck Depression Inventory were used to confirm that patients were in remission. The Childhood Trauma Questionnaire and Young Schema Questionnaire-Short Form 3 were used to identify childhood traumas and early maladaptive schemas. In bipolar disorder, a positive, low power correlation was observed between the vulnerability to threats schema and emotional, physical and sexual abuse. In the unipolar disorder group, there was a positive, low power correlation between the emotional inhibition, failure, approval seeking, dependence, abandonment and defectiveness schemas and social isolation, and a positive, moderate correlation between social isolation and emotional abuse. Individuals with bipolar disorder suffered greater childhood trauma compared to subjects with unipolar disorder and healthy individuals. Greater maladaptive schema activation were present in individuals with bipolar disorder compared to those with unipolar disorder and healthy individuals.

  12. Ketamine for Treatment-Resistant Unipolar Depression

    Science.gov (United States)

    Mathew, Sanjay J.; Shah, Asim; Lapidus, Kyle; Clark, Crystal; Jarun, Noor; Ostermeyer, Britta; Murrough, James W.

    2013-01-01

    Currently available drugs for unipolar major depressive disorder (MDD), which target monoaminergic systems, have a delayed onset of action and significant limitations in efficacy. Antidepressants with primary pharmacological targets outside the monoamine system may offer the potential for more rapid activity with improved therapeutic benefit. The glutamate system has been scrutinized as a target for antidepressant drug discovery. The purpose of this article is to review emerging literature on the potential rapid-onset antidepressant properties of the glutamate NMDA receptor antagonist ketamine, an established anaesthetic agent. The pharmacology of ketamine and its enantiomer S-ketamine is reviewed, followed by examples of its clinical application in chronic, refractory pain conditions, which are commonly co-morbid with depression. The first generation of studies in patients with treatment-resistant depression (TRD) reported the safety and acute efficacy of a single subanaesthetic dose (0.5 mg/kg) of intravenous ketamine. A second generation of ketamine studies is focused on testing alternate routes of drug delivery, identifying methods to prevent relapse following resolution of depressive symptoms and understanding the neural basis for the putative antidepressant actions of ketamine. In addition to traditional depression rating endpoints, ongoing research is examining the impact of ketamine on neurocognition. Although the first clinical report in MDD was published in 2000, there is a paucity of adequately controlled double-blind trials, and limited clinical experience outside of research settings. Given the potential risks of ketamine, safety considerations will ultimately determine whether this old drug is successfully repositioned as a new therapy for TRD. PMID:22303887

  13. Defining the light emitting area for displays in the unipolar regime of highly efficient light emitting transistors

    Science.gov (United States)

    Ullah, Mujeeb; Armin, Ardalan; Tandy, Kristen; Yambem, Soniya D.; Burn, Paul L.; Meredith, Paul; Namdas, Ebinazar B.

    2015-01-01

    Light-emitting field effect transistors (LEFETs) are an emerging class of multifunctional optoelectronic devices. It combines the light emitting function of an OLED with the switching function of a transistor in a single device architecture. The dual functionality of LEFETs has the potential applications in active matrix displays. However, the key problem of existing LEFETs thus far has been their low EQEs at high brightness, poor ON/OFF and poorly defined light emitting area - a thin emissive zone at the edge of the electrodes. Here we report heterostructure LEFETs based on solution processed unipolar charge transport and an emissive polymer that have an EQE of up to 1% at a brightness of 1350 cd/m2, ON/OFF ratio > 104 and a well-defined light emitting zone suitable for display pixel design. We show that a non-planar hole-injecting electrode combined with a semi-transparent electron-injecting electrode enables to achieve high EQE at high brightness and high ON/OFF ratio. Furthermore, we demonstrate that heterostructure LEFETs have a better frequency response (fcut-off = 2.6 kHz) compared to single layer LEFETs. The results presented here therefore are a major step along the pathway towards the realization of LEFETs for display applications. PMID:25743444

  14. The Unipolar illusion: Why new great powers will rise

    Energy Technology Data Exchange (ETDEWEB)

    Layne, C.

    The Soviet Union's collapse transformed the international system from bipolarity to unipolarity. To be sure, the United States has not imposed a [open quotes]universal monarchy[close quotes] on the international system. There are other states that are formidable militarily (Russia) or economically (Japan and Germany).[close quote] However, because only the United States possesses imposing strength in all categories of great power capability, it enjoys a preeminent role in international politics. Following the Gulf War and the Soviet Union's collapse, many commentators suggested that America should adopt a new grand strategy that would aim at perpetuating unipolarity. Belief that unipolarity favors the United States, and hence should be maintained, resonated in official Washington as well.

  15. Rate and predictors of conversion from unipolar to bipolar disorder

    DEFF Research Database (Denmark)

    Kessing, Lars Vedel; Willer, Inge Stoel; Andersen, Per Kragh

    2017-01-01

    OBJECTIVES: For the first time to present a systematic review and meta-analysis of the conversion rate and predictors of conversion from unipolar disorder to bipolar disorder. METHODS: A systematic literature search up to October 2016 was performed. For the meta-analysis, we only included studies...... that used survival analysis to estimate the conversion rate. RESULTS: A total of 31 studies were identified, among which 11 used survival analyses, including two register-based studies. The yearly rate of conversion to bipolar disorder decreased with time from 3.9% in the first year after study entry...... with a diagnosis of unipolar disorder to 3.1% in years 1-2, 1.0% in years 2-5 and 0.8% in years 5-10. A total of eight risk factors were evaluated comprising gender, age at onset of unipolar disorder, number of depressive episodes, treatment resistance to antidepressants, family history of bipolar disorder...

  16. Sleep patterns and the risk for unipolar depression: a review

    Science.gov (United States)

    Wiebe, Sabrina T; Cassoff, Jamie; Gruber, Reut

    2012-01-01

    Psychological disorders, particularly mood disorders, such as unipolar depression, are often accompanied by comorbid sleep disturbances, such as insomnia, restless sleep, and restricted sleep duration. The nature of the relationship between unipolar depression and these sleep disturbances remains unclear, as sleep disturbance may be a risk factor for development, an initial manifestation of the disorder, or a comorbid condition affected by similar mechanisms. Various studies have examined the impact of sleep deprivation on the presence of (or exacerbation of) depressive symptoms, and have examined longitudinal and concurrent associations between different sleep disturbances and unipolar depression. This review examines the evidence for sleep disturbances as a risk factor for the development and presence of depression, as well as examining common underlying mechanisms. Clinical implications pertaining to the comorbid nature of various sleep patterns and depression are considered. PMID:23620679

  17. Electronic properties of blue phosphorene/graphene and blue phosphorene/graphene-like gallium nitride heterostructures.

    Science.gov (United States)

    Sun, Minglei; Chou, Jyh-Pin; Yu, Jin; Tang, Wencheng

    2017-07-05

    Blue phosphorene (BlueP) is a graphene-like phosphorus nanosheet which was synthesized very recently for the first time [Nano Lett., 2016, 16, 4903-4908]. The combination of electronic properties of two different two-dimensional materials in an ultrathin van der Waals (vdW) vertical heterostructure has been proved to be an effective approach to the design of novel electronic and optoelectronic devices. Therefore, we used density functional theory to investigate the structural and electronic properties of two BlueP-based heterostructures - BlueP/graphene (BlueP/G) and BlueP/graphene-like gallium nitride (BlueP/g-GaN). Our results showed that the semiconducting nature of BlueP and the Dirac cone of G are well preserved in the BlueP/G vdW heterostructure. Moreover, by applying a perpendicular electric field, it is possible to tune the position of the Dirac cone of G with respect to the band edge of BlueP, resulting in the ability to control the Schottky barrier height. For the BlueP/g-GaN vdW heterostructure, BlueP forms an interface with g-GaN with a type-II band alignment, which is a promising feature for unipolar electronic device applications. Furthermore, we discovered that both G and g-GaN can be used as an active layer for BlueP to facilitate charge injection and enhance the device performance.

  18. Electrically-Generated Spin Polarization in Non-Magnetic Semiconductors

    Science.gov (United States)

    2016-03-31

    AFRL-AFOSR-VA-TR-2016-0143 Electrically-generated spin polarization in non -magnetic semiconductors Vanessa Sih UNIVERSITY OF MICHIGAN Final Report 03...SUBTITLE (YIP) - Electrically-generated spin polarization in non -magnetic semiconductors 5a. CONTRACT NUMBER 5b. GRANT NUMBER FA9550-12-1-0258 5c...that produced electrically-generated electron spin polarization in non -magnetic semiconductor heterostructures. Electrically-generated electron spin

  19. Unipolar arcing phenomena observed in laboratory and nature

    Energy Technology Data Exchange (ETDEWEB)

    Sanduloviciu, M. [Al. I. Cuza Univ. (Romania)

    1995-12-31

    Unipolar arcing phenomena observed as coherent {open_quotes}plasma{close_quotes} balls operating on a surface of constant potential are explained in the frame of a new already proposed self-organisation mechanism considered at the origin of the formation and stability of extended coherent structures observed in plasma devices.

  20. Executive functions in young patients with unipolar depression

    Directory of Open Access Journals (Sweden)

    Totić-Poznanović Sanja

    2006-01-01

    Full Text Available Neuropsychological deficits associated with unipolar depression are seen in a broad range of cognitive domains. Executive deficits may be prominent in depression. Investigation of executive functions in younger adult patients with unipolar depression has been the focus of our study. Twenty-two consecutively depressive inpatients (24-36 years and 21 healthy control subjects, matched on age, gender, education and verbal IQ were included in the study. Neuropsychological tests for executive functions were applied to all subjects. Unipolar young depressives showed significantly reduced number of completed categories and more trials for completion of the first category on Wisconsin Card Sorting Test (WCST. No difference of tasks assessing the short-term memory, total errors on WCST, perseverative and non-perseverative errors, and of both phonemic and semantic conditions of verbal fluency was found between groups. The results suggested that unipolar depressives had specific cognitive style characterized by "negative cognitive set" (stronger negative reaction to negative feedback and by failure to use negative feedback to improve their performance.

  1. A Ge/Si heterostructure nanowire-based double quantum dot with integrated charge sensor

    OpenAIRE

    Hu, Yongjie; Churchill, Hugh; Reilly, David; Xiang, Jie; Lieber, Charles; M. Marcus, Charles

    2007-01-01

    Coupled electron spins in semiconductor double quantum dots hold promise as the basis for solid-state qubits. To date, most experiments have used III-V materials, in which coherence is limited by hyperfine interactions. Ge/Si heterostructure nanowires seem ideally suited to overcome this limitation: the predominance of spin-zero nuclei suppresses the hyperfine interaction and chemical synthesis creates a clean and defect-free system with highly controllable properties. Here we present a top g...

  2. Spin Orbit Interaction Engineering for beyond Spin Transfer Torque memory

    Science.gov (United States)

    Wang, Kang L.

    Spin transfer torque memory uses electron current to transfer the spin torque of electrons to switch a magnetic free layer. This talk will address an alternative approach to energy efficient non-volatile spintronics through engineering of spin orbit interaction (SOC) and the use of spin orbit torque (SOT) by the use of electric field to improve further the energy efficiency of switching. I will first discuss the engineering of interface SOC, which results in the electric field control of magnetic moment or magneto-electric (ME) effect. Magnetic memory bits based on this ME effect, referred to as magnetoelectric RAM (MeRAM), is shown to have orders of magnitude lower energy dissipation compared with spin transfer torque memory (STTRAM). Likewise, interests in spin Hall as a result of SOC have led to many advances. Recent demonstrations of magnetization switching induced by in-plane current in heavy metal/ferromagnetic heterostructures have been shown to arise from the large SOC. The large SOC is also shown to give rise to the large SOT. Due to the presence of an intrinsic extraordinarily strong SOC and spin-momentum lock, topological insulators (TIs) are expected to be promising candidates for exploring spin-orbit torque (SOT)-related physics. In particular, we will show the magnetization switching in a chromium-doped magnetic TI bilayer heterostructure by charge current. A giant SOT of more than three orders of magnitude larger than those reported in heavy metals is also obtained. This large SOT is shown to come from the spin-momentum locked surface states of TI, which may further lead to innovative low power applications. I will also describe other related physics of SOC at the interface of anti-ferromagnetism/ferromagnetic structure and show the control exchange bias by electric field for high speed memory switching. The work was in part supported by ERFC-SHINES, NSF, ARO, TANMS, and FAME.

  3. Physics and Applications of Unipolar Barriers in Infrared (IR) Detectors

    Science.gov (United States)

    2016-08-23

    APPLIED PHYSICS LETTERS 106, 173505 (2015) 0003-6951/2015/106(17)/173505/4/$30.00 CV 2015 AIP Publishing LLC This article is copyrighted as... Physics Letters 106, 173505 (2015); doi: 10.1063/1.4919450 View online: http://dx.doi.org/10.1063/1.4919450 View Table of Contents: http...AFRL-RV-PS- TR-2016-0120 AFRL-RV-PS- TR-2016-0120 PHYSICS AND APPLICATIONS OF UNIPOLAR BARRIERS IN INFRARED (IR) DETECTORS Gary Wicks University

  4. Sleep patterns and the risk for unipolar depression: a review

    Directory of Open Access Journals (Sweden)

    Wiebe ST

    2012-05-01

    Full Text Available Sabrina T Wiebe, Jamie Cassoff, Reut GruberAttention, Behavior and Sleep Laboratory, Douglas Mental Health University Institute, Montréal; McGill University, Montréal, Quebec, CanadaAbstract: Psychological disorders, particularly mood disorders, such as unipolar depression, are often accompanied by comorbid sleep disturbances, such as insomnia, restless sleep, and restricted sleep duration. The nature of the relationship between unipolar depression and these sleep disturbances remains unclear, as sleep disturbance may be a risk factor for development, an initial manifestation of the disorder, or a comorbid condition affected by similar mechanisms. Various studies have examined the impact of sleep deprivation on the presence of (or exacerbation of depressive symptoms, and have examined longitudinal and concurrent associations between different sleep disturbances and unipolar depression. This review examines the evidence for sleep disturbances as a risk factor for the development and presence of depression, as well as examining common underlying mechanisms. Clinical implications pertaining to the comorbid nature of various sleep patterns and depression are considered.Keywords: sleep, depression, insomnia, sleep deprivation, development

  5. Unipolar Mania: Recent Updates and Review of the Literature

    Directory of Open Access Journals (Sweden)

    Shubham Mehta

    2014-01-01

    Full Text Available Introduction. Unipolar mania (UM has received less than the expected attention, when compared to its contemporary mood disorders, unipolar depression (UD and bipolar disorder (BD. Method. The literature search included PUBMED and PSYCINFO databases. Cross-searches of key references were made to identify other articles of importance. Results. There seems to be a bipolar subgroup with a stable, unipolar recurrent manic course. Although UM does not have significant differences from bipolar mania in terms of sociodemographic variables, there are certain significant differences in clinical features. UM is reported to have more grandiosity, psychotic symptoms, and premorbid hyperthymic temperament, but less rapid cycling, suicidality, seasonality, and comorbid anxiety disorders. It seems to have a better course of illness with better social and professional adjustment. However, its response to lithium prophylaxis is found to be poor as compared to classical BD and valproate could be a better choice in this case. Conclusion. The available literature suggests that UM has certain differences from classical BD. The evidence, however, is insufficient to categorize it as separate diagnostic entity. However, considering UM as a course specifier of BD would be a reasonable step.

  6. Early Maladaptive Schemas Related to Unipolar and Bipolar Depression: Similarities and Differences

    Directory of Open Access Journals (Sweden)

    Nergis LAPSEKİLİ

    2012-11-01

    Full Text Available Objective and methodology: Cognitive theory of depression has begun to examine the difference between bipolar and unipolar depression in the context of thinking features. Yet, little is known about the same and seperated points of bipolar and unipolar depression. The objective is evaluating relationship between cognitive schemas of bipolar and unipolar patients. Bipolar and unipolar depression patients and a control group were enrolled in the study. Beck Depression Inventory, Young Mania Scale and Young Schema Questionnaire were administered to the groups. Results: There was significant difference between unipolar and control groups in “Abandonment/instability”. In “mistrust/ abuse” significant difference was between unipolar and bipolar and between unipolar and control groups. ln “entitlement/self-centeredness” difference was between unipolar and control groups. In all other schemas, difference was between unipolar and control and bipolar and control groups. In these schemas, control group had significantly lower scores than others. Unipolar and bipolar groups were similar. Conclusion: In patient groups, schemas like defectiveness, incompetence, failure, vulnerability to danger and undeveloped self were indicative of low self-perception. This case draws attention to distortions in self-perception. When the absence of difference between bipolar and controls in “mistrust/abuse” and “abandonment/instability” schemas is evaluated in terms of cognitive triad, it is suggested that environmental perspective in this group of patients did not exhibit pessimistic features. The only significantly different schema between unipolar and bipolar groups was “mistrust/ abuse”. This suggests that bipolar group didn’t have negative thoughts like unipolar patients about the perception of the enviroment.

  7. Magnetoelectric control of spin currents

    Energy Technology Data Exchange (ETDEWEB)

    Gómez, J. E.; Vargas, J. M.; Avilés-Félix, L.; Butera, A. [Centro Atómico Bariloche, Instituto de Nanociencia y Nanotecnología (CNEA) and Conicet, 8400 Bariloche, Río Negro (Argentina)

    2016-06-13

    The ability to control the spin current injection has been explored on a hybrid magnetoelectric system consisting of a (011)-cut ferroelectric lead magnesium niobate-lead titanate (PMNT) single crystal, a ferromagnetic FePt alloy, and a metallic Pt. With this PMNT/FePt/Pt structure we have been able to control the magnetic field position or the microwave excitation frequency at which the spin pumping phenomenon between FePt and Pt occurs. We demonstrate that the magnetoelectric heterostructure operating in the L-T (longitudinal magnetized-transverse polarized) mode couples the PMNT crystal to the magnetostrictive FePt/Pt bilayer, displaying a strong magnetoelectric coefficient of ∼140 Oe cm kV{sup −1}. Our results show that this mechanism can be effectively exploited as a tunable spin current intensity emitter and open the possibility to create an oscillating or a bistable switch to effectively manipulate spin currents.

  8. Fabrication and Characterization of a Single Hole Transistor in p-type GaAs/AlGaAs Heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Tracy, Lisa A [Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States); Reno, John L. [Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States); Hargett, Terry W. [Sandia National Laboratories (SNL-NM), Albuquerque, NM (United States)

    2015-09-01

    Most spin qubit research to date has focused on manipulating single electron spins in quantum dots. However, hole spins are predicted to have some advantages over electron spins, such as reduced coupling to host semiconductor nuclear spins and the ability to control hole spins electrically using the large spin-orbit interaction. Building on recent advances in fabricating high-mobility 2D hole systems in GaAs/AlGaAs heterostructures at Sandia, we fabricate and characterize single hole transistors in GaAs. We demonstrate p-type double quantum dot devices with few-hole occupation, which could be used to study the physics of individual hole spins and control over coupling between hole spins, looking towards eventual applications in quantum computing. Intentionally left blank

  9. Ultrafast Study of Dynamic Exchange Coupling in Ferromagnet/Oxide/Semiconductor Heterostructures

    Science.gov (United States)

    Ou, Yu-Sheng

    Spintronics is the area of research that aims at utilizing the quantum mechanical spin degree of freedom of electrons in solid-state materials for information processing and data storage application. Since the discovery of the giant magnetoresistance, the field of spintronics has attracted lots of attention for its numerous potential advantages over contemporary electronics, such as less power consumption, high integration density and non-volatility. The realization of a spin battery, defined by the ability to create spin current without associated charge current, has been a long-standing goal in the field of spintronics. The demonstration of pure spin current in ferromagnet/nonmagnetic material hybrid structures by ferromagnetic resonance spin pumping has defined a thrilling direction for this field. As such, this dissertation targets at exploring the spin and magnetization dynamics in ferromagnet/oxide/semiconductor heterostructures (Fe/MgO/GaAs) using time-resolved optical pump-probe spectroscopy with the long-range goal of understanding the fundamentals of FMR-driven spin pumping. Fe/GaAs heterostructures are complex systems that contain multiple spin species, including paramagnetic spins (GaAs electrons), nuclear spins (Ga and As nuclei) and ferromagnetic spins (Fe). Optical pump-probe studies on their interplay have revealed a number of novel phenomena that has not been explored before. As such they will be the major focus of this dissertation. First, I will discuss the effect of interfacial exchange coupling on the GaAs free-carrier spin relaxation. Temperature- and field-dependent spin-resolved pump-probe studies reveal a strong correlation of the electron spin relaxation with carrier freeze-out, in quantitative agreement with a theoretical interpretation that at low temperatures the free-carrier spin lifetime is dominated by inhomogeneity in the local hyperfine field due to carrier localization. Second, we investigate the impact of tunnel barrier thickness

  10. Multilayer Graphene–WSe2 Heterostructures for WSe2 Transistors

    KAUST Repository

    Tang, Hao-Ling

    2017-11-29

    Two-dimensional (2D) materials are drawing growing attention for next-generation electronics and optoelectronics owing to its atomic thickness and unique physical properties. One of the challenges posed by 2D materials is the large source/drain (S/D) series resistance due to their thinness, which may be resolved by thickening the source and drain regions. Recently explored lateral graphene–MoS21−3 and graphene–WS21,4 heterostructures shed light on resolving the mentioned issues owing to their superior ohmic contact behaviors. However, recently reported field-effect transistors (FETs) based on graphene–TMD heterostructures have only shown n-type characteristics. The lack of p-type transistor limits their applications in complementary metal-oxide semiconductor electronics. In this work, we demonstrate p-type FETs based on graphene–WSe2 lateral heterojunctions grown with the scalable CVD technique. Few-layer WSe2 is overlapped with the multilayer graphene (MLG) at MLG–WSe2 junctions such that the contact resistance is reduced. Importantly, the few-layer WSe2 only forms at the junction region while the channel is still maintained as a WSe2 monolayer for transistor operation. Furthermore, by imposing doping to graphene S/D, 2 orders of magnitude enhancement in Ion/Ioff ratio to ∼108 and the unipolar p-type characteristics are obtained regardless of the work function of the metal in ambient air condition. The MLG is proposed to serve as a 2D version of emerging raised source/drain approach in electronics.

  11. A Ge/Si heterostructure nanowire-based double quantum dot with integrated charge sensor

    DEFF Research Database (Denmark)

    Hu, Yongjie; Churchill, Hugh; Reilly, David

    2007-01-01

    Coupled electron spins in semiconductor double quantum dots hold promise as the basis for solid-state qubits. To date, most experiments have used III-V materials, in which coherence is limited by hyperfine interactions. Ge/Si heterostructure nanowires seem ideally suited to overcome this limitation......: the predominance of spin-zero nuclei suppresses the hyperfine interaction and chemical synthesis creates a clean and defect-free system with highly controllable properties. Here we present a top gate-defined double quantum dot based on Ge/Si heterostructure nanowires with fully tunable coupling between the dots...... and to the leads. We also demonstrate a novel approach to charge sensing in a one-dimensional nanostructure by capacitively coupling the double dot to a single dot on an adjacent nanowire. The double quantum dot and integrated charge sensor serve as an essential building block required to form a solid-state spin...

  12. Cognitions in bipolar affective disorder and unipolar depression: imagining suicide.

    Science.gov (United States)

    Hales, Susie A; Deeprose, Catherine; Goodwin, Guy M; Holmes, Emily A

    2011-01-01

    Bipolar disorder has the highest rate of suicide of all the psychiatric disorders. In unipolar depression, individuals report vivid, affect-laden images of suicide or the aftermath of death (flashforwards to suicide) during suicidal ideation but this phenomenon has not been explored in bipolar disorder. Therefore the authors investigated and compared imagery and verbal thoughts related to past suicidality in individuals with bipolar disorder (n = 20) and unipolar depression (n = 20). The study used a quasi-experimental comparative design. The Structured Clinical Interview for DSM-IV was used to confirm diagnoses. Quantitative and qualitative data were gathered through questionnaire measures (e.g., mood and trait imagery use). Individual interviews assessed suicidal cognitions in the form of (i) mental images and (ii) verbal thoughts. All participants reported imagining flashforwards to suicide. Both groups reported greater preoccupation with these suicide-related images than with verbal thoughts about suicide. However, compared to the unipolar group, the bipolar group were significantly more preoccupied with flashforward imagery, rated this imagery as more compelling, and were more than twice as likely to report that the images made them want to take action to complete suicide. In addition, the bipolar group reported a greater trait propensity to use mental imagery in general. Suicidal ideation needs to be better characterized, and mental imagery of suicide has been a neglected but potentially critical feature of suicidal ideation, particularly in bipolar disorder. Our findings suggest that flashforward imagery warrants further investigation for formal universal clinical assessment procedures. © 2011 John Wiley and Sons A/S.

  13. Predominant polarity and temperament in bipolar and unipolar affective disorders.

    Science.gov (United States)

    Mazzarini, Lorenzo; Pacchiarotti, Isabella; Colom, Francesc; Sani, Gabriele; Kotzalidis, Giorgio D; Rosa, Adriane R; Sanna, Livia; De Rossi, Pietro; Girardi, Nicoletta; Bonnin, C Mar; Sanchez-Moreno, Jose; Vazquez, Gustavo H; Gasto, Cristobal; Tatarelli, Roberto; Vieta, Eduard

    2009-12-01

    Recently, the concept of predominant polarity (two-thirds of episodes belonging to a single pole of the illness) has been introduced to further characterise subtypes of bipolar disorders. This concept has been proven to have diagnostic and therapeutic implications, but little is known on the underlying psychopathology and temperaments. With this study, we aimed to further validate the concept and explore its relationships with temperament. This study enrolled 143 patients with bipolar or unipolar disorder. We analysed predominant polarity in the sample of bipolar I patients (N=124), focussing on those who showed a clear predominance for one or the other polarity, and distinguishing manic/hypomanic (MP) from depressive polarity (DP), and a unipolar major depression (UP) group (N=19),. We also assessed temperament by means of the Temperament Evaluation of the Memphis, Pisa, Paris, and San Diego Autoquestionnaire (TEMPS-A). Over 55% of the bipolar I sample fulfilled predominant polarity criteria, with two-thirds of those meeting criteria for MP and one third for DP. MP and DP were similar in scoring higher than UP on the hyperthymic/cyclothymic scales of the TEMPS-A; the UP group scored higher on the anxious/depressive scales. Our results show that both bipolar I MP and DP subgroups are temperamentally similar and different from UP. Depression in DP bipolar I patients should be viewed as the overlap of depression on a hyperthymic/cyclothymic temperament. These findings confirm the value of the predominant polarity concept as well as the importance of temperaments to separate bipolar from unipolar disorders.

  14. A novel unipolar converter for switched reluctance motor

    Science.gov (United States)

    Le-Huy, Hoang; Viarouge, Philippe; Francoeur, Bruno

    1990-10-01

    A configuration of a unipolar converter with improved switching performance suitable for switched-reluctance motor supply is presented. The switched-reluctance motor operation principle is presented, and its ideal characteristics are considered. The proposed converter is described, and its operation is analyzed. The converter characteristics are studied with the aid of computer simulation. Current control of the proposed converter is considered. A prototype converter has been built to verify the analysis results and to validate the simulation. The design procedure is presented, and experimental results which confirm the analysis are given and discussed.

  15. Interpersonal problems in social phobia versus unipolar depression.

    Science.gov (United States)

    Stangier, Ulrich; Esser, Frank; Leber, Simone; Risch, Anne K; Heidenreich, Thomas

    2006-01-01

    In this study we compared interpersonal problems in outpatients with social phobia (n=50) to those with unipolar depressive disorders (n=50). All participants completed the Inventory of Interpersonal Problems. Multivariate analyses of variance revealed significant group differences. Individuals with social phobia had significantly lower scores on the primary dimension of Control and significantly higher values on the Social Avoidance subscale than did individuals with depression. Our results support findings from former analogue studies. They indicate that social phobia is associated with severe social relationship problems that should be considered in treatment.

  16. Heterostructures of transition metal dichalcogenides

    KAUST Repository

    Amin, Bin

    2015-08-24

    The structural, electronic, optical, and photocatalytic properties of out-of-plane and in-plane heterostructures of transition metal dichalcogenides are investigated by (hybrid) first principles calculations. The out-of-plane heterostructures are found to be indirect band gap semiconductors with type-II band alignment. Direct band gaps can be achieved by moderate tensile strain in specific cases. The excitonic peaks show blueshifts as compared to the parent monolayer systems, whereas redshifts occur when the chalcogen atoms are exchanged along the series S-Se-Te. Strong absorption from infrared to visible light as well as excellent photocatalytic properties can be achieved.

  17. Engineering multiple topological phases in nanoscale Van der Waals heterostructures: realisation of α-antimonene

    Science.gov (United States)

    Märkl, T.; Kowalczyk, P. J.; Le Ster, M.; Mahajan, I. V.; Pirie, H.; Ahmed, Z.; Bian, G.; Wang, X.; Chiang, T.-C.; Brown, S. A.

    2018-01-01

    Van der Waals heterostructures have recently been identified as providing many opportunities to create new two-dimensional materials, and in particular to produce materials with topologically-interesting states. Here we show that it is possible to create such heterostructures with multiple topological phases in a single nanoscale island. We discuss their growth within the framework of diffusion-limited aggregation, the formation of moiré patterns due to the differing crystallographies of the materials comprising the heterostructure, and the potential to engineer both the electronic structure as well as local variations of topological order. In particular we show that it is possible to build islands which include both the hexagonal β- and rectangular α-forms of antimonene, on top of the topological insulator α-bismuthene. This is the first experimental realisation of α-antimonene, and we show that it is a topologically non-trivial material in the quantum spin Hall class.

  18. Seasonal variation of depressive symptoms in unipolar major depressive disorder.

    Science.gov (United States)

    Cobb, Bryan S; Coryell, William H; Cavanaugh, Joseph; Keller, Martin; Solomon, David A; Endicott, Jean; Potash, James B; Fiedorowicz, Jess G

    2014-11-01

    Retrospective and cross-sectional studies of seasonal variation of depressive symptoms in unipolar major depression have yielded conflicting results. We examined seasonal variation of mood symptoms in a long-term prospective cohort - the Collaborative Depression Study (CDS). The sample included 298 CDS participants from five academic centers with a prospectively derived diagnosis of unipolar major depression who were followed for at least ten years of annual or semi-annual assessments. Generalized linear mixed models were utilized to investigate the presence of seasonal patterns. In a subset of 271 participants followed for at least 20 years, the stability of a winter depressive pattern was assessed across the first two decades of follow-up. A small increase in proportion of time depressed was found in the months surrounding the winter solstice, although the greatest symptom burden was seen in December through April with a peak in March. The relative burden of winter depressive symptoms in the first decade demonstrated no relationship to that of the second decade. The onset of new episodes was highest October through January, peaking in January. There exists a small but statistically significant peak in depressive symptoms from the month of the winter solstice to the month of the spring equinox. However, the predominance of winter depressive symptoms did not appear stable over the long-term course of illness. Copyright © 2014 Elsevier Inc. All rights reserved.

  19. Seasonal Variation of Depressive Symptoms in Unipolar Major Depressive Disorder

    Science.gov (United States)

    Cobb, Bryan S.; Coryell, William H.; Cavanaugh, Joseph; Keller, Martin; Solomon, David A.; Endicott, Jean; Potash, James B.; Fiedorowicz, Jess G.

    2014-01-01

    Objectives Retrospective and cross-sectional studies of seasonal variation of depressive symptoms in unipolar major depression have yielded conflicting results. We examined seasonal variation of mood symptoms in a long-term prospective cohort – the Collaborative Depression Study (CDS). Methods The sample included 298 CDS participants from five academic centers with a prospectively derived diagnosis of unipolar major depression who were followed for at least ten years of annual or semi-annual assessments. Generalized linear mixed models were utilized to investigate the presence of seasonal patterns. In a subset of 271 participants followed for at least 20 years, the stability of a winter depressive pattern was assessed across the first two decades of follow-up. Results A small increase in proportion of time depressed was found in the months surrounding the winter solstice, although the greatest symptom burden was seen in December through April with a peak in March. The relative burden of winter depressive symptoms in the first decade demonstrated no relationship to that of the second decade. The onset of new episodes was highest October through January, peaking in January. Conclusions There exists a small but statistically significant peak in depressive symptoms from the month of the winter solstice to the month of the spring equinox. However, the predominance of winter depressive symptoms did not appear stable over the long-term course of illness. PMID:25176622

  20. Escher-like quasiperiodic heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Barriuso, A G; Monzon, J J; Sanchez-Soto, L L [Departamento de Optica, Facultad de Fisica, Universidad Complutense, 28040 Madrid (Spain); Costa, A F [Departamento de Matematicas Fundamentales, Facultad de Ciencias, Universidad Nacional de Educacion a Distancia, Senda del Rey 9, 28040 Madrid (Spain)

    2009-05-15

    Quasiperiodic heterostructures present unique structural, electronic and vibrational properties, connected to the existence of incommensurate periods. We go beyond previous schemes, such as Fibonacci or Thue-Morse, based on substitutional sequences, by introducing construction rules generated by tessellations of the unit disc by regular polygons. We explore some of the properties exhibited by these systems. (fast track communication)

  1. Excellent valleytronic properties and nontrivial topological phase in germanene heterostructure

    Science.gov (United States)

    Qu, Jinfeng; Peng, Xiangyang; Luo, Chaobo; Zhong, Jianxin

    2017-10-01

    In comparison with transition metal dichalcogenides (TMDs), germanene is not an ideal valleytronic material due to its very weak spin–orbit coupling (SOC) and tiny band gap. By performing density functional calculations, we studied the heterostructures of germanene/Sb and germanene/SbF in order to augment the valleytronic properties of germanene to a level similar to that of TMDs. Although germanene/Sb has large spin splittings, the system is found to be gapless. By proximity with the fluorine-adsorbed Sb layer, germanene can acquire large SOC. Germanene/SbF has a sizable direct band gap at Dirac points and the Dirac valleys of SbF and germanene are preserved in the heterostructure. The Ge–SbF interaction breaks the inversion symmetry, leading to large spin splittings and Berry curvatures, which are valley contrasting due to time reversal symmetry. We studied the interband optical transitions and found that valley polarization is achievable via valley-selective circular dichroism. The calculated Z 2 topological invariant further confirms that Ge/SbF is a topological insulator. Our studies illustrate that weak SOC materials can be converted into good valleytronic material and that nontrivial topological phase and valleytronic properties can be simultaneously realized.

  2. Unipolar radiofrequency treatment to improve the appearance of cellulite.

    Science.gov (United States)

    Alexiades-Armenakas, Macrene; Dover, Jeffrey S; Arndt, Kenneth A

    2008-09-01

    Previous studies suggest that radiofrequency (RF) energy may be effective as a treatment for cellulite. This bilateral paired blinded comparative study assesses the efficacy and safety of a unipolar RF device for improving the appearance of cellulite using a new quantitative cellulite grading system. In this randomized, blinded, split-design study, 10 individuals (aged 32-57 years) with a clinically observable excess of subcutaneous fat and cellulite (minimum grade 2 out of 4) on the thighs received up to six unilateral treatments (number of treatments at the investigator's discretion) at 2-week intervals with unipolar RF. The untreated side of the thigh served as an internal control. Treated thighs were randomly assigned by alternate allocation. Results were evaluated using study participant questionnaires and by two blinded evaluators (JSD, KAA) using photographs and the author's (MAA) cellulite grading scale at each treatment visit and at 1-month and 3-month follow-up visits after the final treatment. A novel quantitative four-point cellulite grading system is presented and applied, which separately grades dimple density, dimple distribution, dimple depth, diameter and contour. All participants responded to treatment (mean of 4.22 and range of three to six treatments). The blinded evaluations of photographs using the cellulite grading scale demonstrated the following mean grading scores for the treated leg versus the control leg: dimple density of 2.73 vs 3.18 (11.25% mean improvement), dimple distribution 2.89 vs 3.32 (10.75% mean improvement), dimple depth 1.47 vs 1.54 (2.5% mean improvement), and mean score of 2.36 (SEM 0.45) vs 2.68 (SEM 0.57) (8.00+/-2.84% mean improvement). The treatment was painless and side effects included minimal to moderate erythema which resolved within 1 to 3 hours. No crusting, scarring or dyspigmentation was observed. This randomized, blinded, split-design, controlled study employing a quantitative four-point grading scale

  3. Interface currents and magnetization in singlet-triplet superconducting heterostructures: Role of chiral and helical domains

    Science.gov (United States)

    Romano, Alfonso; Noce, Canio; Vekhter, Ilya; Cuoco, Mario

    2017-08-01

    Chiral and helical domain walls are generic defects of topological spin-triplet superconductors. We study theoretically the magnetic and transport properties of superconducting singlet-triplet-singlet heterostructure as a function of the phase difference between the singlet leads in the presence of chiral and helical domains inside the spin-triplet region. The local inversion symmetry breaking at the singlet-triplet interface allows the emergence of a static phase-controlled magnetization and generally yields both spin and charge currents flowing along the edges. The parity of the domain wall number affects the relative orientation of the interface moments and currents, while in some cases the domain walls themselves contribute to spin and charge transport. We demonstrate that singlet-triplet heterostructures are a generic prototype to generate and control nondissipative spin and charge effects, putting them in a broader class of systems exhibiting spin-Hall, anomalous Hall effects and similar phenomena. Features of the electron transport and magnetic effects at the interfaces can be employed to assess the presence of domains in chiral/helical superconductors.

  4. Quantum spin Hall phase in multilayer graphene

    Science.gov (United States)

    García-Martínez, N. A.; Lado, J. L.; Fernández-Rossier, J.

    2015-06-01

    The so-called quantum spin Hall phase is a topologically nontrivial insulating phase that is predicted to appear in graphene and graphenelike systems. In this paper we address the question of whether this topological property persists in multilayered systems. We consider two situations: purely multilayer graphene and heterostructures where graphene is encapsulated by trivial insulators with a strong spin-orbit coupling. We use a four-orbital tight-binding model that includes full atomic spin-orbit coupling and we calculate the Z2 topological invariant of the bulk states as well as the edge states of semi-infinite crystals with armchair termination. For homogeneous multilayers we find that even when the spin-orbit interaction opens a gap for all possible stackings, only those with an odd number of layers host gapless edge states while those with an even number of layers are trivial insulators. For heterostructures where graphene is encapsulated by trivial insulators, it turns out that interlayer coupling is able to induce a topological gap whose size is controlled by the spin-orbit coupling of the encapsulating materials, indicating that the quantum spin Hall phase can be induced by proximity to trivial insulators.

  5. Is There Such a Diagnosis as an Early Onset Unipolar Depression?

    Directory of Open Access Journals (Sweden)

    Berta Ferreira

    2014-10-01

    Full Text Available According to Kraepelin, melancholia was part of manic-depressive psychosis. In the 60s however, other authors (Angst, 1966; Perris, 1966; Winokur, 1967 questioned this concept by considering unipolar depression a clinical entity, separated from bipolar disorders. Using strict bipolar disorders criteria, some prospective studies have shown a diagnosis switch from unipolar to bipolar disorders in up to 50% of the cases (Caryell, 1995; Goldberg, 2001; Angst, 2005. The existence of unipolar depression as a clinical entity is discussed, taking in consideration the “minor” bipolar symptoms that occur during the course of affective disorders.

  6. Bibliotherapy in unipolar depression: a meta-analysis.

    Science.gov (United States)

    Cuijpers, P

    1997-06-01

    In the last decades, several therapies for unipolar depression have been developed, for example cognitive therapy, behavior therapy and pharmacotherapy. A new kind of therapy is bibliotherapy. What is new in this treatment modality is not the content, because bibliotherapy usually uses a cognitive-behavioral approach. Only the form in which it is presented is new. In bibliotherapy the patient takes a standardized treatment home, in book form, and works it through more or less independently. Contacts with therapists are only supportive or facilitative. No traditional relationship between therapist and patient is developed. In this article the relevance of bibliotherapy for the clinical practice is presented and a meta-analysis of the research into bibliotherapy is described.

  7. Understanding the social interaction difficulties of women with unipolar depression.

    Science.gov (United States)

    Rice, Niamh M; Grealy, Madeleine A; Javaid, Aisha; Millan Serrano, Rosa

    2011-10-01

    Poor social functioning is a prevalent complaint of unipolar depression, but subjective experiences of social interactions have not been systematically studied. A limited number of qualitative researchers have specifically addressed the social difficulties in depression. We conducted in-depth semistructured interviews with 11 depressed women. Thematic analysis was used to analyze the transcripts. Five themes emerged. The first two, diminished desire to socially interact and fear of social interactions, encompass perceptions that have not been previously reported. The third theme, the pressure to adhere to social norms, provided support for previous findings. The final two themes, the perceptions of others and isolation, elaborated on existing knowledge. We found that difficulties with social engagements are much broader than previously reported, with a lack of interest in others, being too emotionally overloaded to interact, perceptions that other people will not understand how women with depression are feeling, and fears of being a burden all contributing to the difficulties experienced in depression.

  8. Undoped strained germanium quantum wells towards spin qubits

    Science.gov (United States)

    Scappucci, Giordano; Sammak, Amir; Yeoh, Lareine; Sabbagh, Diego; Conesa-Boj, Sonia; Kolling, Sebastian; Zaumseil, Peter; Capellini, Giovanni

    Germanium is emerging as a promising material to implement spin qubits because of the key properties of high carrier mobility, strong spin-orbit coupling, long spin coherence times and compatibility with silicon technology. We report the deposition of undoped strained Ge/SiGe quantum wells of high structural quality in a reduced pressure chemical vapor deposition tool. Structural analysis of the Ge/SiGe heterostructures confirm sharp interfaces, full relaxation of the virtual substrate, and coherent deposition of the strained quantum well. Furthermore, we will discuss architectures towards the development of CMOS compatible spin qubits in laterally defined Ge quantum dots. .

  9. Pure spin current devices based on ferromagnetic topological insulators

    Science.gov (United States)

    Götte, Matthias; Joppe, Michael; Dahm, Thomas

    2016-01-01

    Two-dimensional topological insulators possess two counter propagating edge channels with opposite spin direction. Recent experimental progress allowed to create ferromagnetic topological insulators realizing a quantum anomalous Hall (QAH) state. In the QAH state one of the two edge channels disappears due to the strong ferromagnetic exchange field. We investigate heterostructures of topological insulators and ferromagnetic topological insulators by means of numerical transport calculations. We show that spin current flow in such heterostructures can be controlled with high fidelity. Specifically, we propose spintronic devices that are capable of creating, switching and detecting pure spin currents using the same technology. In these devices electrical currents are directly converted into spin currents, allowing a high conversion efficiency. Energy independent transport properties in combination with large bulk gaps in some topological insulator materials may allow operation even at room temperature. PMID:27782187

  10. Conductance of Rashba spin-split systems with ferromagnetic contacts

    DEFF Research Database (Denmark)

    Larsen, M. Høgsbro; Lunde, A.M.; Flensberg, Karsten

    2002-01-01

    We study theoretically the conductance of heterostructures with ferromagnetic (F) conductors and a two-dimensional electron gas with Rashba (R) spin-orbit interaction using a two-channel Landauer formula. Assuming a one-dimensional model, we first find the S matrix for the FR interface. This result...

  11. Electron spin and charge in semiconductor quantum dots

    NARCIS (Netherlands)

    Elzerman, J.M.

    2004-01-01

    In this thesis, the spin and charge degree of freedom of electrons in semiconductor lateral and vertical quantum dots are experimentally investigated. The lateral quantum dot devices are defined in a two-dimensional electron gas (2DEG) below the surface of a GaAs/AlGaAs heterostructure, by metallic

  12. Sheath-limited unipolar induction in the solar wind. [plasma interactions with solar system bodies

    Science.gov (United States)

    Srnka, L. J.

    1975-01-01

    A model of the steady-state interaction between the solar wind and an electrically conducting body having neither an atmosphere nor an intrinsic magnetic field sufficient enough to deflect the plasma flow is presented which considers some effects of a plasma surface sheath on unipolar induction. The Sonett-Colburn (1967, 1968) unipolar dynamo model is reviewed, and it is noted that the unipolar dynamo response of an electrically conducting body in the solar wind's motional field can be controlled by sheath effects in certain cases where the body radius is less than a certain critical value. It is shown that sheath effects do not limit the unipolar response of the moon or Mercury since their body radii are much larger than their critical radii. Sheath effects are also considered for asteroids, the Martian satellites, the irregular Jovian satellites, the outer satellites of Saturn, and meteorite parent bodies in a primordial enhanced solar wind.

  13. Study on High Current PWM Unipolar Four Phases Driver for Stepper Motor Control

    Directory of Open Access Journals (Sweden)

    Alexandru Morar

    2013-06-01

    Full Text Available This paper presents the study on high – current PWM, unipolar stepper motor controller/driver, are remarkable for simplicity, high – reliability, multifunctional facilities for four phases hybrid stepper motor.

  14. Spin current

    CERN Document Server

    Valenzuela, Sergio O; Saitoh, Eiji; Kimura, Takashi

    2012-01-01

    In a new branch of physics and technology called spin-electronics or spintronics, the flow of electrical charge (usual current) as well as the flow of electron spin, the so-called 'spin current', are manipulated and controlled together. This book provides an introduction and guide to the new physics and application of spin current.

  15. PSYCHOPATHOLOGICAL CHARACTERISTICS OF BIPOLAR AND UNIPOLAR DEPRESSION - POTENTIAL INDICATORS OF BIPOLARITY

    OpenAIRE

    Motovsky, Branislav; Pecenak, Jan

    2013-01-01

    Background: Establishing whether a depressive episode is part of a unipolar or bipolar disorder is essential for treatment planning. Over recent years, a growing number of publications have discussed psychopathological characteristics that might serve as indicators of bipolarity in patients with a history of depression dominated by unipolar symptoms. Our primary aim was to verify the adequacy of these indicators in contributing to a precise diagnosis in everyday clinical practice. ...

  16. Novel electronic properties of a new MoS{sub 2}/TiO{sub 2} heterostructure and potential applications in solar cells and photocatalysis

    Energy Technology Data Exchange (ETDEWEB)

    Li, Yanhua [State Key Laboratory of Coal Disaster Dynamics and Control, Department of Applied Physics, Chongqing University, Chongqing 400044 (China); Cai, Congzhong, E-mail: czcai@cqu.edu.cn [State Key Laboratory of Coal Disaster Dynamics and Control, Department of Applied Physics, Chongqing University, Chongqing 400044 (China); Gu, Yonghong [State Key Laboratory of Coal Disaster Dynamics and Control, Department of Applied Physics, Chongqing University, Chongqing 400044 (China); Chongqing Key Laboratory on Optoelectronic Functional Materials, Chongqing Normal University, Chongqing 401331 (China); Cheng, Wende [State Key Laboratory of Coal Disaster Dynamics and Control, Department of Applied Physics, Chongqing University, Chongqing 400044 (China); Department of Physics, Chongqing University of Science and Technology, Chongqing 401331 (China); Xiong, Wen [Department of Physics, Chongqing University, Chongqing 401331 (China); Zhao, Chengjun [State Key Laboratory of Coal Disaster Dynamics and Control, Department of Applied Physics, Chongqing University, Chongqing 400044 (China)

    2017-08-31

    Highlights: • The Moiré patterns of a new MoS{sub 2}/TiO{sub 2} heterostructure are investigated. • The novel electronic properties of the new heterostructure are discovered. • The MoS{sub 2}/TiO{sub 2} superlattice is found to have similar electronic properties to the bilayer heterostructure. • Two novel design schemes based on the MoS{sub 2}/TiO{sub 2} heterostructure and superlattice are proposed for a solar cell and photocatalyst, respectively. - Abstract: The structural and electronic properties of two-dimensional (2D) MoS{sub 2}/TiO{sub 2} heterostructure with a special configuration of Moiré pattern have been investigated for the first time using first-principles methods with van der Waals correction. It is found that the new van der Waals heterostructure is of a type-II band alignment between the MoS{sub 2} and TiO{sub 2} layers, and the electronic structures of monolayer MoS{sub 2} and 2D TiO{sub 2} are well retained in their respective layers due to a weak interlayer coupling, which suggests that the heterostructure may have potential applications in many fields such as photoelectric devices, photocatalysis, energy conversion and storage, etc. Meanwhile, the heterostructure can also provide an ideal platform of two-dimensional electron gas (2DEG) and two-dimensional hole gas (2DHG) for fundamental research such as spin Hall effect, etc. In addition, it is discovered that the corresponding MoS{sub 2}/TiO{sub 2} superlattice also has similar electronic properties to MoS{sub 2}/TiO{sub 2} bilayer heterostructure. Furthermore, two novel design schemes based on the MoS{sub 2}/TiO{sub 2} heterostructure and superlattice are proposed for a solar cell and photocatalyst, respectively.

  17. A prospective randomized study comparing unipolar versus bipolar hysteroscopic myomectomy in infertile women

    Directory of Open Access Journals (Sweden)

    Kallol K Roy

    2017-01-01

    Full Text Available Study Objective: To compare the operative and reproductive outcome of hysteroscopic myomectomy using unipolar resectoscope versus bipolar resectoscope in patients with infertility and menorrhagia. Design: Randomized, prospective, parallel, comparative, single-blinded study. Design Classification: Canadian Task Force classification I. Setting: Tertiary care institute. Patients: Sixty women with submucous myoma and infertility. Interventions: Hysteroscopic myomectomy performed with unipolar resectoscope or bipolar resectoscope. Measurements: Primary outcome measures were the pregnancy-related indicators. Secondary outcome measures were the operative parameters, harmful outcomes related to the procedure, and comparison of improvement levels in the menstrual pattern after surgery between the two groups. Main Results: A total of 60 patients were randomized into two groups of equal size. Baseline characteristics were not significantly different between the two groups. Reduction in sodium level from pre- to postsurgery was significantly (P = 0.001 higher in the unipolar group. Nine patients (30% in the unipolar group had hyponatremia in the postoperative period compared to none in the bipolar group (P = 0.002. However, there was no significant difference in the other operative parameters between the two groups. In both the groups, a significant improvement in the menstrual symptoms was observed after myomectomy. Pregnancy-related outcomes were similar in both the groups. Conclusion: The use of bipolar resectoscope for hysteroscopic myomectomy is associated with lesser risk of hyponatremia compared to unipolar resectoscope. Bipolar resectoscopic myomectomy is found to be an effective and safer alternative to unipolar resectoscopy with similar reproductive outcome.

  18. Efficient spin filter using multi-terminal quantum dot with spin-orbit interaction

    Directory of Open Access Journals (Sweden)

    Yokoyama Tomohiro

    2011-01-01

    Full Text Available Abstract We propose a multi-terminal spin filter using a quantum dot with spin-orbit interaction. First, we formulate the spin Hall effect (SHE in a quantum dot connected to three leads. We show that the SHE is significantly enhanced by the resonant tunneling if the level spacing in the quantum dot is smaller than the level broadening. We stress that the SHE is tunable by changing the tunnel coupling to the third lead. Next, we perform a numerical simulation for a multi-terminal spin filter using a quantum dot fabricated on semiconductor heterostructures. The spin filter shows an efficiency of more than 50% when the conditions for the enhanced SHE are satisfied. PACS numbers: 72.25.Dc,71.70.Ej,73.63.Kv,85.75.-d

  19. Nanomagnet Applications in Multiferroic Heterostructures

    OpenAIRE

    Li, Xu

    2017-01-01

    Over the past decade there have been considerable research efforts directed at controlling spin dynamics in nanomagnets. Spin dynamics generally covers two regimes, one is large amplitude motion associated with equilibrium magnetization state change with storage media applications that use parallel and antiparallel magnetization configurations to represent “0” and “1” states of memory bits. The other type is small amplitude oscillation, wherein spin precesses around its equilibrium state with...

  20. Effect of Rashba and Dresselhaus Spin-Orbit Couplings on Electron Spin Polarization in a Hybrid Magnetic-Electric Barrier Nanostructure

    Science.gov (United States)

    Yang, Shi-Peng; Lu, Mao-Wang; Huang, Xin-Hong; Tang, Qiang; Zhou, Yong-Long

    2017-04-01

    A theoretical study has been carried out on the spin-dependent electron transport in a hybrid magnetic-electric barrier nanostructure with both Rashba and Dresselhaus spin-orbit couplings, which can be experimentally realized by depositing a ferromagnetic strip and a Schottky metal strip on top of a semiconductor heterostructure. The spin-orbit coupling-dependent transmission coefficient, conductance, and spin polarization are calculated by solving the Schrödinger equation exactly with the help of the transfer-matrix method. We find that both the magnitude and sign of the electron spin polarization vary strongly with the spin-orbit coupling strength. Thus, the degree of electron spin polarization can be manipulated by properly adjusting the spin-orbit coupling strength, and such a nanosystem can be employed as a controllable spin filter for spintronics applications.

  1. Magnetic equivalent circuit model for unipolar hybrid excitation synchronous machine

    Directory of Open Access Journals (Sweden)

    Kupiec Emil

    2015-03-01

    Full Text Available Lately, there has been increased interest in hybrid excitation electrical machines. Hybrid excitation is a construction that combines permanent magnet excitation with wound field excitation. Within the general classification, these machines can be classified as modified synchronous machines or inductor machines. These machines may be applied as motors and generators. The complexity of electromagnetic phenomena which occur as a result of coupling of magnetic fluxes of separate excitation systems with perpendicular magnetic axis is a motivation to formulate various mathematical models of these machines. The presented paper discusses the construction of a unipolar hybrid excitation synchronous machine. The magnetic equivalent circuit model including nonlinear magnetization curves is presented. Based on this model, it is possible to determine the multi-parameter relationships between the induced voltage and magnetomotive force in the excitation winding. Particular attention has been paid to the analysis of the impact of additional stator and rotor yokes on above relationship. Induced voltage determines the remaining operating parameters of the machine, both in the motor and generator mode of operation. The analysis of chosen correlations results in an identification of the effective control range of electromotive force of the machine.

  2. Administration of ketamine for unipolar and bipolar depression.

    Science.gov (United States)

    Kraus, Christoph; Rabl, Ulrich; Vanicek, Thomas; Carlberg, Laura; Popovic, Ana; Spies, Marie; Bartova, Lucie; Gryglewski, Gregor; Papageorgiou, Konstantinos; Lanzenberger, Rupert; Willeit, Matthäus; Winkler, Dietmar; Rybakowski, Janusz K; Kasper, Siegfried

    2017-03-01

    Clinical trials demonstrated that ketamine exhibits rapid antidepressant efficacy when administered in subanaesthetic dosages. We reviewed currently available literature investigating efficacy, response rates and safety profile. Twelve studies investigating unipolar, seven on bipolar depression were included after search in medline, scopus and web of science. Randomized, placebo-controlled or open-label trials reported antidepressant response rates after 24 h on primary outcome measures at 61%. The average reduction of Hamilton Depression Rating Scale (HAM-D) was 10.9 points, Beck Depression Inventory (BDI) 15.7 points and Montgomery-Asberg Depression Rating Scale (MADRS) 20.8 points. Ketamine was always superior to placebo. Most common side effects were dizziness, blurred vision, restlessness, nausea/vomiting and headache, which were all reversible. Relapse rates ranged between 60% and 92%. To provide best practice-based information to patients, a consent-form for application and modification in local language is included. Ketamine constitutes a novel, rapid and efficacious treatment option for patients suffering from treatment resistant depression and exhibits rapid and significant anti-suicidal effects. New administration routes might serve as alternative to intravenous regimes for potential usage in outpatient settings. However, long-term side effects are not known and short duration of antidepressant response need ways to prolong ketamine's efficacy.

  3. Excitation of dielectric barrier discharges by unipolar submicrosecond square pulses

    Science.gov (United States)

    Liu, Shuhai; Neiger, Manfred

    2001-06-01

    Dielectric barrier discharges (DBDs) are self-extinguishing discharges due to charge accumulation on dielectric surfaces. In order to take advantage of these surface charges also at a low repetition frequency, high-voltage unipolar square pulses (amplitude up to 15 kV, rise and fall time less than 20 ns) are applied to drive DBDs. For electrical diagnostics of this novel excitation method, a temporally dynamic model for diffuse DBDs is introduced, from which equations were derived which allow the calculation of internal electrical quantities in the discharge gap from measured external electrical quantities. It was found, following a primary discharge at the rising front or at the top of the voltage pulse, that a secondary discharge is induced at the end of the falling voltage flank without simultaneously consuming energy from the external circuit. The energy needed is provided by the accumulated surface and space charges left by the primary discharge, which are totally or partially lost under normal low-frequency sine or square wave excitation. Secondary discharges are observed in a wide range of electrode configurations, gases and gas pressures for both homogeneous and filamentary discharges. In the case of filamentary modes, secondary discharges are found to develop along the remaining channels of the preceding primary discharges. Experiments for ozone synthesis show an improved energy efficiency of 8-9 eV per ozone molecule, which is about 30% better than that achieved with sine wave excitation.

  4. Pharmacological treatment of unipolar depressive disorders: summary of WFSBP guidelines.

    Science.gov (United States)

    Bauer, Michael; Severus, Emanuel; Möller, Hans-Jürgen; Young, Allan H

    2017-09-01

    Major depressive disorder (MDD) is a severe mood disorder affecting individuals of all ages and is characterised by single or recurrent major depressive episodes. Key elements of acute and maintenance treatment of MDD include pharmacotherapy, and psychological approaches such as psychoeducation and adherence monitoring. This summary of the 'Practice guidelines for the biological treatment of unipolar depressive disorders' comprises acute, continuation and maintenance treatment developed by an international Task Force of the World Federation of Societies of Biological Psychiatry (WFSBP), and focuses on pharmacological treatment options. A variety of different antidepressants are available for the effective acute and prophylactic treatment of depressed patients. Randomised placebo-controlled efficacy studies indicate that all major classes of antidepressants are effective in acute treatment but also in preventing recurrence of depression showing about a two-fold higher relapse rate with placebo treatment. Evidence suggests that the 'newer' antidepressants have superior long-term effectiveness due to better tolerability and safety profile compared to traditional antidepressants, e.g., the tricyclic antidepressants (TCA). Despite progress in the availability of different treatment options there is still a substantial proportion of patients who do not achieve full remission. Several add-on pharmacological treatment options are among the best-evidenced strategies for refractory depressed patients.

  5. CAG repeat expansions in bipolar and unipolar disorders

    Energy Technology Data Exchange (ETDEWEB)

    Oruc, L.; Verheyen, G.R.; Raeymaekers, P.; Van Broeckhoven, C. [Univ. of Antwerp (Belgium)] [and others

    1997-03-01

    Family, twin, and adoption studies consistently have indicated that the familial aggregation of bipolar (BP) disorder and unipolar recurrent major depression (UPR) is accounted for largely by genetic factors. However, the mode of inheritance is complex. One of the possible explanations could be that a gene with variable penetrance and variable expression is involved. Recently there have been reports on a new class of genetic diseases caused by an abnormal trinucleotide-repeat expansion (TRE). In a number of genetic disorders, these dynamic mutations were proved to be the biological basis for the clinically observed phenomenon of anticipation. DNA consisting of repeated triplets of nucleotides becomes unstable and increases in size over generations within families, giving rise to an increased severity and/or an earlier onset of the disorder. It has been recognized for a long time that anticipation occurs in multiplex families transmitting mental illness. More recent studies also suggest that both BP disorder and UPR show features that are compatible with anticipation. Although the findings of anticipation in BP disorders and in UPR must be interpreted with caution because of the possible presence of numerous ascertainment biases, they support the hypothesis that pathological TREs are implicated in the transmission of these disorders. TRE combined with variable penetrance of expression could explain the complex transmission pattern observed in BP disorder. In view of this, the recent reports of an association between CAG-repeat length and BP disorder in a Belgian, Swedish, and British population are promising. 14 refs., 1 fig., 1 tab.

  6. The bipolar nature of charge resident on supposedly unipolar aerosols

    Science.gov (United States)

    O'Leary, M.; Balachadran, W.; Rogueda, P.; Chambers, F.

    2008-12-01

    Interest in aerosol electrostatic properties for optimisation of drug delivery within the lung has varied over time. The availability of the Dekati Electrostatic Low Pressure Impactor (ELPI) has facilitated several recent papers investigating distributions of aerosol size and charge. The ELPI operates in a similar fashion to conventional impactors fractionating the aerosol population by aerodynamic size. The impactor plates are electrically conducting and connected to electrometers allowing measurement of inherent aerosol charge transferred upon impaction. Results from pMDIs showing varying charge polarity with size have been cited as evidence of the bipolar nature of charge output. Sum charge over an aerosol measured by the ELPI is, however, simply net charge that may be seen to evolve with size. Electrostatic particle capture methods have been used to assess the nature of the charge resident on a pMDI aerosol population demonstrating unipolar output on the ELPI and have shown consistent bipolarity. Net charge output would have been measured as possessing single polarity but would consist of larger magnitude positive and negative components. Even moderate levels of bipolarity render as inherently flawed any attempt to characterise the level of charge on individual aerosol droplets or the entire population based solely on net charge data.

  7. Alterations of niacin skin sensitivity in recurrent unipolar depressive disorder.

    Science.gov (United States)

    Smesny, Stefan; Baur, Kati; Rudolph, Nicole; Nenadic, Igor; Sauer, Heinrich

    2010-08-01

    Skin flushing after niacin (methylnicotinate, vitamin B(3)) stimulation is a biological marker of availability of polyunsaturated fatty acids (PUFA). Decreased PUFA levels have been reported in depressive disorder, while add-on supplementation of omega-3 PUFA has been suggested to improve depressive symptoms. This study aimed to clarify whether a disturbance of niacin skin flushing occurs also in depression, and to identify patient characteristics for those who might benefit from PUFA supplementation. We studied 30 patients with recurrent unipolar depressive disorder during a major depressive episode (treated with antidepressants), and 30 healthy volunteers matched for age and gender. Aqueous methylnicotinate was applied in three dilution steps (0.001M, 0.01M, and 0.1M) onto the inner forearm skin. Skin flushing was assessed in three-minute intervals over 15min using optical reflection spectroscopy. While there was no overall difference in skin flushing between patients and controls, niacin sensitivity was inversely correlated with severity of symptoms, and flush deficits were significantly associated with depressed mood, feelings of anxiety and somatic symptoms (loss of appetite and weight loss). Results are suggestive of a subgroup of depressive patients characterised by a specific symptom cluster and disturbed niacin skin flushing. Copyright 2009 Elsevier B.V. All rights reserved.

  8. Enhanced Spin Conductance of a Thin-Film Insulating Antiferromagnet

    Science.gov (United States)

    Bender, Scott A.; Skarsvâg, Hans; Brataas, Arne; Duine, Rembert A.

    2017-08-01

    We investigate spin transport by thermally excited spin waves in an antiferromagnetic insulator. Starting from a stochastic Landau-Lifshitz-Gilbert phenomenology, we obtain the out-of-equilibrium spin-wave properties. In linear response to spin biasing and a temperature gradient, we compute the spin transport through a normal-metal-antiferromagnet-normal-metal heterostructure. We show that the spin conductance diverges as one approaches the spin-flop transition; this enhancement of the conductance should be readily observable by sweeping the magnetic field across the spin-flop transition. The results from such experiments may, on the one hand, enhance our understanding of spin transport near a phase transition, and on the other be useful for applications that require a large degree of tunability of spin currents. In contrast, the spin Seebeck coefficient does not diverge at the spin-flop transition. Furthermore, the spin Seebeck coefficient is finite even at zero magnetic field, provided that the normal metal contacts break the symmetry between the antiferromagnetic sublattices.

  9. Partial hybridisation of electron-hole states in an InAs/GaSb double quantum well heterostructure

    Science.gov (United States)

    Knox, C. S.; Morrison, C.; Herling, F.; Ritchie, D. A.; Newell, O.; Myronov, M.; Linfield, E. H.; Marrows, C. H.

    2017-10-01

    InAs/GaSb coupled quantum well heterostructures are important semiconductor systems with applications ranging from spintronics to photonics. Most recently, InAs/GaSb heterostructures have been identified as candidate two-dimensional topological insulators, predicted to exhibit helical edge conduction via fully spin-polarised carriers. We study an InAs/GaSb double quantum well heterostructure with an AlSb barrier to decouple partially the 2D electrons and holes, and find conduction consistent with a 2D hole gas, with an effective mass of 0.235 ± 0.005 m 0, existing simultaneously with hybridised carriers with an effective mass of 0.070 ± 0.005 m 0, where m 0 is the bare electron mass.

  10. EUO-Based Multifunctional Heterostructures

    Science.gov (United States)

    2015-06-06

    MULTIFUNCTIONAL HETEROSTRUCTURES Final Report (June, 2015) 5 5 A. Melville, T. Mairoser, A. Schmehl, D.E. Shai, E.J. Monkman, J.W. Harter , T. Heeg...Europium Oxide,” J. Appl. Phys. 109 (2011) 07C309. 13 D.E. Shai, A.J. Melville, J.W. Harter , E.J. Monkman, D.W. Shen, A. Schmehl, D.G. Schlom, and...A. Schmehl, D.E. Shai, E.J. Monkman, J.W. Harter , T. Heeg, B. Holländer, J. Schubert, K.M. Shen, J. Mannhart, and D.G. Schlom, “Lutetium-doped EuO

  11. Electrotunable artificial molecules based on van der Waals heterostructures.

    Science.gov (United States)

    Zhang, Zhuo-Zhi; Song, Xiang-Xiang; Luo, Gang; Deng, Guang-Wei; Mosallanejad, Vahid; Taniguchi, Takashi; Watanabe, Kenji; Li, Hai-Ou; Cao, Gang; Guo, Guang-Can; Nori, Franco; Guo, Guo-Ping

    2017-10-01

    Quantum confinement has made it possible to detect and manipulate single-electron charge and spin states. The recent focus on two-dimensional (2D) materials has attracted significant interests on possible applications to quantum devices, including detecting and manipulating either single-electron charging behavior or spin and valley degrees of freedom. However, the most popular model systems, consisting of tunable double-quantum-dot molecules, are still extremely difficult to realize in these materials. We show that an artificial molecule can be reversibly formed in atomically thin MoS2 sandwiched in hexagonal boron nitride, with each artificial atom controlled separately by electrostatic gating. The extracted values for coupling energies at different regimes indicate a single-electron transport behavior, with the coupling strength between the quantum dots tuned monotonically. Moreover, in the low-density regime, we observe a decrease of the conductance with magnetic field, suggesting the observation of Coulomb blockade weak anti-localization. Our experiments demonstrate for the first time the realization of an artificial quantum-dot molecule in a gated MoS2 van der Waals heterostructure, which could be used to investigate spin-valley physics. The compatibility with large-scale production, gate controllability, electron-hole bipolarity, and new quantum degrees of freedom in the family of 2D materials opens new possibilities for quantum electronics and its applications.

  12. Ab initio exploration of d0 digital magnetic heterostructures: the case of MgO and CaO δ-doped with potassium

    Science.gov (United States)

    Du, Jiangtao; Dong, Shengjie; Lu, Yi-Lin; Zhao, Hui; Wang, Liying; Feng, Liefeng

    2017-06-01

    Previous studies of digital magnetic heterostructures have mainly focused on 3 d transition metal δ-doped semiconductors. In this work, sp-electron digital magnetic heterostructures without magnetic ions are proposed. Based on a theoretical density functional investigation, electronic structures and magnetic properties of MgO and CaO δ-doped with K were reported. The results show that these heterostructures are half-metallic ferromagnetic materials having semiconducting up spins and metallic down spins, with an exchange interaction much stronger than that of a random alloy with similar K concentration. Our first-principles calculations show that the carriers at the Fermi level are strongly confined within a few monolayers around the KO plane. This strong confinement is responsible for the large exchange coupling and the two-dimensional half-metallic behavior. The thickness of the host semiconducting spacer does not significantly change the global electric and magnetic features.

  13. Room-Temperature Spin-Orbit Torque Switching Induced by a Topological Insulator

    Science.gov (United States)

    Han, Jiahao; Richardella, A.; Siddiqui, Saima A.; Finley, Joseph; Samarth, N.; Liu, Luqiao

    2017-08-01

    The strongly spin-momentum coupled electronic states in topological insulators (TI) have been extensively pursued to realize efficient magnetic switching. However, previous studies show a large discrepancy of the charge-spin conversion efficiency. Moreover, current-induced magnetic switching with TI can only be observed at cryogenic temperatures. We report spin-orbit torque switching in a TI-ferrimagnet heterostructure with perpendicular magnetic anisotropy at room temperature. The obtained effective spin Hall angle of TI is substantially larger than the previously studied heavy metals. Our results demonstrate robust charge-spin conversion in TI and provide a direct avenue towards applicable TI-based spintronic devices.

  14. Two-Fluid Theory for Spin Superfluidity in Magnetic Insulators.

    Science.gov (United States)

    Flebus, B; Bender, S A; Tserkovnyak, Y; Duine, R A

    2016-03-18

    We investigate coupled spin and heat transport in easy-plane magnetic insulators. These materials display a continuous phase transition between normal and condensate states that is controlled by an external magnetic field. Using hydrodynamic equations supplemented by Gross-Pitaevski phenomenology and magnetoelectric circuit theory, we derive a two-fluid model to describe the dynamics of thermal and condensed magnons, and the appropriate boundary conditions in a hybrid normal-metal-magnetic-insulator-normal-metal heterostructure. We discuss how the emergent spin superfluidity can be experimentally probed via a spin Seebeck effect measurement.

  15. Resistive Detection of Single Electron Motion and Spin Resonance

    Science.gov (United States)

    Jiang, Hongwen; Yablonovitch, Eli; Wang, Kang; Roychowdhury, Vwani; Divincenzo, David

    2000-03-01

    For any of the quantum computing proposals involving spin states in solids, the spin orientations of individual qubit has to be measured at the end of the operations. In the design of the spin-resonance-transistors, a conventional field-effect-transistor (FET) channel is used to accomplish this seemingly almost impossible task. Toward this end, we have performed a sequence of exploratory experiments in Si and GaAs based FET devices. Current noise spectrum in a short channel Si FET, known as the random telegraph signal, is measured for different temperatures and gate voltages. Using a GaAs/AlGaAs heterostructure, we have detected electron spin resonance of a spin-split Landau level by a transport measurement in microwave fields. The extension of our results to the actual implementation of the spin-resonance-transistors will be discussed.

  16. Eye movement in unipolar depression and bipolar disorders: A systematic review of the literature

    Directory of Open Access Journals (Sweden)

    Nicolas eCarvalho

    2015-12-01

    Full Text Available Background:The analysis of eye movements (EM by eye-tracking has been carried out for several decades to investigate mood regulation, emotional information processing, and psychomotor disturbances in depressive disorders. Method:A systematic review of all English language PubMed articles using the terms saccadic eye movements OR eye-tracking AND depression OR bipolar disorders was conducted using PRISMA guidelines. The aim of this review was to identify the specific alterations of EM in unipolar and bipolar disorders. Results:Unipolar depression has been characterized by an increase in reaction time in prosaccade and antisaccade tasks, and a specific attraction for negative pictures. Bipolar disorders have been associated with an increase in reaction time in prosaccade and antisaccade tasks, and an attraction for threatening images. Methodological limitations include mixed samples sometimes undifferentiating unipolar and bipolar patients, or an absence of specification regarding the polarity of the episode in bipolar disorders. Moreover, we found no study explicitly comparing EM in both unipolar depression and bipolar disorders.Conclusion: Unipolar depression and bipolar disorders can be characterized by different psychomotor alterations and affective regulation strategies. Eye movement analysis could be a useful tool as a potential biomarker to distinguish between the two diseases. However, further research is needed to directly and systematically compare eye movement data in both diseases under strictly identical experimental conditions.

  17. Cognitive impairment in the remitted state of unipolar depressive disorder: A systematic review

    DEFF Research Database (Denmark)

    Hasselbalch, Bo Jacob; Knorr, Ulla; Kessing, Lars Vedel

    2010-01-01

    BACKGROUND: It is unclear whether cognitive impairment is prevalent in the remitted state of unipolar disorder. AIM: To evaluate whether cognitive function is impaired in the remitted state in patients with unipolar depression compared with healthy control individuals, and to investigate the asso......BACKGROUND: It is unclear whether cognitive impairment is prevalent in the remitted state of unipolar disorder. AIM: To evaluate whether cognitive function is impaired in the remitted state in patients with unipolar depression compared with healthy control individuals, and to investigate...... the association to prior course of illness, i.e. the number, duration and severity of prior depressive episodes. METHOD: Systematic search on existing on-line databases and hand-search of original published papers. RESULTS: A total of 11 studies fulfilled the selection criteria and were included in the review......, including a total of 500 patients remitted from unipolar depression and 471 healthy control individuals. In nine of the eleven studies performance on neuropsychological tests was found to be decreased in patients compared to healthy control individuals in at least one of the tests. Methodological drawbacks...

  18. Stabilized thin film heterostructure for electrochemical applications

    DEFF Research Database (Denmark)

    2015-01-01

    The invention provides a method for the formation of a thin film multi-layered heterostructure upon a substrate, said method comprising the steps of: a. providing a substrate; b. depositing a buffer layer upon said substrate, said buffer layer being a layer of stable ionic conductor (B); c...... or less; and e. repeating steps b. and c. a total of N times, such that N repeating pairs of layers (A/B) are built up, wherein N is 1 or more. The invention also provides a thin film multi-layered heterostructure as such, and the combination of a thin film multi-layered heterostructure and a substrate...

  19. Strain engineered magnetic tunnel junctions and spin-orbit torque switching (Conference Presentation)

    Science.gov (United States)

    Wu, Yang; Narayanapillai, Kulothungasagaran; Elyasi, Mehrdad; Qiu, Xuepeng; Yang, Hyunsoo

    2016-10-01

    The efficient generation of pure spin currents and manipulation of the magnetization dynamics of magnetic structures is of central importance in the field of spintronics. The spin-orbit effect is one of the promising ways to generate spin currents, in which a charge current can be converted to a transverse spin current due to the spin-orbit interaction. We investigate the spin dynamics in the presence of strong spin-orbit coupling materials such as LaAlO3/SrTiO3 oxide heterostructures. Angle dependent magnetoresistance measurements are employed to detect and understand the current-induced spin-orbit torques, and an effective field of 2.35 T is observed for a dc-current of 200 uA. In order to understand the interaction between light and spin currents, we use a femtosecond laser to excite an ultrafast transient spin current and subsequent terahertz (THz) emission in nonmagnet (NM)/ferromagnet (FM)/oxide heterostructures. The THz emission strongly relies on spin-orbit interaction, and is tailored by the magnitude and sign of the effective spin Hall angle of the NM. Our results can be utilized for ultrafast spintronic devices and tunable THz sources.

  20. Cognitive dysfunction in unipolar depression: implications for treatment.

    Science.gov (United States)

    Trivedi, Madhukar H; Greer, Tracy L

    2014-01-01

    The primary objective of this review is to examine the literature assessing abnormalities in neural circuitry and cognition early in the course of major depressive disorder (MDD) and the impact of these features on treatment selection and long-term outcomes. English language and peer-reviewed publications were obtained by PubMed/Medline (www.pubmed.org) searches using combinations of major depressive disorder, major depression, or unipolar depression and "first episode", early, cognition, cognitive, executive function and memory. The terms bipolar and psychosis were excluded from the searches. These searches yielded 409 records. A total of 12 studies, systematic reviews and meta-analyses were selected that evaluated learning, memory and executive function in individuals with major depressive disorder. Additional publications meeting these criteria were identified from the bibliographies of the 12 selected articles and from the "related citations" section of PubMed. Difficulty in concentrating and indecisiveness are reported as among the most troubling symptoms by patients with MDD and may limit functional recovery. Cognitive deficits in memory and decision-making are present early in the course of MDD and may be accompanied by structural abnormalities in the hippocampus and prefrontal cortex involved in cognitive functions. Although resolution of cognitive symptoms of depression lags behind recovery from mood symptoms in many patients, preliminary evidence suggests they may improve with antidepressant therapy, but can also persist residually. New strategies that target cognitive symptoms of depression in addition to mood symptoms are needed to improve long-term outcomes, particularly functional recovery. © 2013 The Authors. Published by Elsevier B.V. All rights reserved.

  1. Research and Experiments on a Unipolar Capacitive Voltage Sensor

    Directory of Open Access Journals (Sweden)

    Qiang Zhou

    2015-08-01

    Full Text Available Voltage sensors are an important part of the electric system. In service, traditional voltage sensors need to directly contact a high-voltage charged body. Sensors involve a large volume, complex insulation structures, and high design costs. Typically an iron core structure is adopted. As a result, ferromagnetic resonance can occur easily during practical application. Moreover, owing to the multilevel capacitor divider, the sensor cannot reflect the changes of measured voltage in time. Based on the electric field coupling principle, this paper designs a new voltage sensor; the unipolar structure design solves many problems of traditional voltage sensors like the great insulation design difficulty and high costs caused by grounding electrodes. A differential signal input structure is adopted for the detection circuit, which effectively restrains the influence of the common-mode interference signal. Through sensor modeling, simulation and calculations, the structural design of the sensor electrode was optimized, miniaturization of the sensor was realized, the voltage division ratio of the sensor was enhanced, and the phase difference of sensor measurement was weakened. The voltage sensor is applied to a single-phase voltage class line of 10 kV for testing. According to the test results, the designed sensor is able to meet the requirements of accurate and real-time measurement for voltage of the charged conductor as well as to provide a new method for electricity larceny prevention and on-line monitoring of the power grid in an electric system. Therefore, it can satisfy the development demands of the smart power grid.

  2. Gauge theory of the long-range proximity effect and spontaneous currents in superconducting heterostructures with strong ferromagnets

    Science.gov (United States)

    Bobkova, I. V.; Bobkov, A. M.; Silaev, M. A.

    2017-09-01

    We present the generalized quasiclassical theory of the long-range superconducting proximity effect in heterostructures with strong ferromagnets, where the exchange splitting is of the order of Fermi energy. In the ferromagnet the propagation of equal-spin Cooper pairs residing on the spin-split Fermi surfaces is shown to be governed by the spin-dependent Abelian gauge field which results either from the spin-orbital coupling or from the magnetic texture. This additional gauge field enters into the quasiclassical equations in superposition with the usual electromagnetic vector potential and results in the generation of spontaneous superconducting currents and phase shifts in various geometries which provide the sources of long-range spin-triplet correlations. We derive the Usadel equations and boundary conditions for the strong ferromagnet and consider several generic examples of the Josephson systems supporting spontaneous currents.

  3. Myers Briggs Type Indicator and Tridimensional Personality Questionnaire differences between bipolar patients and unipolar depressed patients.

    Science.gov (United States)

    Janowsky, D S; Morter, S; Hong, L; Howe, L

    1999-12-01

    The current study was designed to compare personality differences between bipolar patients and unipolar depressed patients, as evaluated on the Myers Briggs Type Indicator (MBTI) and the Tridimensional Personality Questionnaire (TPQ). A group of bipolar and a group of unipolar depressed patients filled out the MBTI, the TPQ, the Beck Depression Inventory, and the CAGE questionnaire. The two groups were compared with each other as to responses on the above surveys, and subgroups of bipolar depressed and bipolar patients with manic symptoms were also compared. Bipolar patients were found to be significantly more extroverted (p = 0.004) and less judging (p = 0.007) on the MBTI. They were significantly more novelty seeking (p = 0.004) and less harm avoidant (p = 0.002) on the TPQ. Of the above differences, only the TPQ harm avoidance scale appeared strongly linked to the patients' level of depression. Significant differences in personality exist between bipolar disorder and unipolar depressed patients.

  4. Device simulation and optimization of laterally-contacted-unipolar-nuclear detector

    CERN Document Server

    Lee, E Y

    1999-01-01

    Unipolar gamma-ray detectors offer the possibility of enhanced energy resolution and detection sensitivity over the conventional planar detectors. However, these detectors are difficult to understand and to fabricate, due to their three-dimensional geometry and multiple electrodes. Computer simulation offers a powerful way to design and to optimize these detectors, by giving the internal electric fields, weighting potentials, and spatially resolved detector responses. Simulation and optimization of an unipolar gamma-ray detector called laterally-contacted-unipolar-nuclear detector (LUND) are shown. For 662 keV gamma-rays from a sup 1 sup 3 sup 7 Cs source, the simulation and optimization of LUND resulted in improvement in the energy resolution from 1.6% to 1.3% and improvement in the active detector volume from 4% to 38% of the total detector volume.

  5. Diagnostic conversion to bipolar disorder in unipolar depressed patients participating in trials on antidepressants

    DEFF Research Database (Denmark)

    Holmskov, J; Licht, R W; Andersen, K

    2017-01-01

    participating in trials on antidepressants, the risk of conversion was associated with the number of previous depressive episodes. Therefore, this study emphasizes that unipolar depressed patients experiencing a relatively high number of recurrences should be followed more closely, or at least be informed about......OBJECTIVE: In unipolar depressed patients participating in trials on antidepressants, we investigated if illness characteristics at baseline could predict conversion to bipolar disorder. METHOD: A long-term register-based follow-up study of 290 unipolar depressed patients with a mean age of 50...... per patient. The risk of conversion was associated with an increasing number of previous depressive episodes at baseline, [HR 1.18, 95% CI (1.10-1.26)]. No association with gender, age, age at first depressive episode, duration of baseline episode, subtype of depression or any of the investigated HAM...

  6. Feasibility of customised unipolar conversion using bipolar temporary pacing wires in patients after surgical repair of congenital heart disease.

    Science.gov (United States)

    Peters, Bjoern; Miera, Oliver; Ewert, Peter; Yilmaz, Sevim; Berger, Felix; Schmitt, Boris

    2014-08-01

    Temporary pacing wires play a crucial role in the diagnosis and therapy of post-operative arrhythmia after surgery for congenital heart disease. At present, bipolar pacing wires are used in most institutions. In case of functional failure of these wires, a unipolar mode of stimulation and sensing should be theoretically possible as a rescue procedure. We tested the feasibility of the customised unipolar mode in 18 post-operative patients with congenital heart disease (age 9.2 ± 13.9 months, weight 6.3 ± 3.8 kg, and cardiopulmonary bypass time 70 ± 29 minutes). As there are two possible unipolar configurations, there are twice the number of testing parameters; of those, we compared sensing (mV) and pacing thresholds (V at 0.5 ms). Atrial sensing was significantly better in the unipolar modes (p < 0.001, p < 0.003). The ventricular unipolar sensing did not differ significantly in the "better" of the two possible configurations from the bipolar values (p = 0.363). For the unipolar pacing thresholds, only the "better" unipolar configuration did not differ significantly from the bipolar measurements (atrial: p = 0.058, ventricular: p = 0.138). There was no exit block or undersensing. The results demonstrate that unipolar stimulation and sensing using bipolar epicardial temporary pacing wires is feasible. In the case of failure of bipolar temporary pacing wires, this modality represents an easy rescue measure that in such cases should always be considered.

  7. Bipolar I and II versus unipolar depression: clinical differences and impulsivity/aggression traits.

    Science.gov (United States)

    Dervic, K; Garcia-Amador, M; Sudol, K; Freed, P; Brent, D A; Mann, J J; Harkavy-Friedman, J M; Oquendo, M A

    2015-01-01

    To investigate distinguishing features between bipolar I, II and unipolar depression, and impulsivity/aggression traits in particular. Six hundred and eighty-five (n=685) patients in a major depressive episode with lifetime Unipolar (UP) depression (n=455), Bipolar I (BP-I) disorder (n=151), and Bipolar II (BP-II) (n=79) disorder were compared in terms of their socio-demographic and clinical characteristics. Compared to unipolar patients, BP-I and BP-II depressed patients were significantly younger at onset of their first depressive episode, and were more likely to experience their first depressive episode before/at age of 15. They also had more previous affective episodes, more first- and second-degree relatives with history of mania, more current psychotic and subsyndromal manic symptoms, and received psychopharmacological and psychotherapy treatment at an earlier age. Furthermore, BP-I and BP-II depressed patients had higher lifetime impulsivity, aggression, and hostility scores. With regard to bipolar subtypes, BP-I patients had more trait-impulsivity and lifetime aggression than BP-II patients whereas the latter had more hostility than BP-I patients. As for co-morbid disorders, Cluster A and B Personality Disorders, alcohol and substance abuse/dependence and anxiety disorders were more prevalent in BP-I and BP-II than in unipolar patients. Whereas the three groups did not differ on other socio-demographic variables, BP-I patients were significantly more often unemployed that UP patients. Our findings comport with major previous findings on differences between bipolar and unipolar depression. As for trait characteristics, bipolar I and II depressed patients had more life-time impulsivity and aggression/hostility than unipolar patients. In addition, bipolar I and II patients also differed on these trait characteristics. Copyright © 2014. Published by Elsevier Masson SAS.

  8. Severe metal-induced osteolysis many years after unipolar hip endoprosthesis.

    Science.gov (United States)

    Mann, Matthew A; Tanzer, Dylan; Tanzer, Michael

    2013-07-01

    Modularity of the femoral head-neck junction provides increased intraoperative flexibility to the surgeon. Complications of this modularity include damage to the trunnion, with subsequent bone and/or soft tissue loss from adverse reactions to metal debris. We describe two cases of severe metal-induced osteolysis and soft tissue damage requiring revision 10 and 13 years following implantation of a unipolar endoprosthesis. Damage to the trunnion resulted in severe acetabular and trochanteric osteolysis and soft tissue loss requiring complex revision surgery. Several reports have shown the trunnion, the head-neck interface, and the neck-stem couple as the causes of this early failure secondary to metal ion release from mechanical fretting corrosion or from crevice corrosion at these modular interfaces. These reports have been in association with a total hip prosthesis rather than a unipolar endoprosthesis. Revision of a unipolar endoprosthesis is most commonly attributable to stem loosening or acetabular erosion from the large femoral head articulating on the host acetabular cartilage and not owing to failure of the trunnion. Trunnion damage resulting in a severe reaction to metal debris with acetabular osteolysis, erosion of the greater trochanter, and loss of the abductor mechanism can occur years after implantation of a cementless unipolar endoprosthesis. This raises questions regarding long-term safety of the modular interface of a contemporary cementless stem and a large-diameter unipolar head. We recommend long-term followup of patients with a unipolar endoprosthesis as early recognition and treatment are required to avoid a potentially complex revision.

  9. Low bone mineral density and high bone metabolism turnover in premenopausal women with unipolar depression.

    Science.gov (United States)

    Petronijević, Milan; Petronijević, Natasa; Ivković, Maja; Stefanović, Dusan; Radonjić, Nevena; Glisić, Branislava; Ristić, Gorica; Damjanović, Aleksandar; Paunović, Vladimir

    2008-03-01

    The majority of studies reporting decreased bone mineral density (BMD) in patients with unipolar depression neglected sex and age differences and menopause as the most important risk factor for osteoporosis. We presumed that physically healthy premenopausal women with unipolar depression have decreased BMD and altered bone cell metabolism. BMD at lumbar spine and femoral neck by dual X-ray absorptiometry, bone alkaline phosphatase sera activity, 5b-tartarate resistant acid phosphatase sera activity and urine N-terminal telopeptide were measured in 73 premenopausal women with unipolar depression and compared with 47 healthy, age- and osteoporosis risk factors-matched premenopausal women. The duration and severity of depression, hormonal status (cortisol, prolactin, parathormone, oestradiol), antidepressive treatment, and physical activity through whole and modified QUALEFFO-41 questionnaire were evaluated. The results were statistically elaborated by the chi-square test, Student's t-test for independent samples, one-way analysis of variance - ANOVA, one-sample Kolmogorov-Smirnov test. Correlations were assessed by means of Pearson's coefficient. Patients with unipolar depression had significantly lower BMD, the decrease of which correlated only with the duration of depression. High bone metabolism turnover was found with a predomination of osteoresorption which, but not osteosynthesis, correlated with the severity of depression, estimated through Hamilton depression scores. Despite higher but not significant levels of cortisol in women with unipolar depression, the BMD decrease and high bone turnover seem not to be the consequence of hormonal changes or medical treatment. The significant correlations between physical activity and osteoresorption markers were found indicating possible underlying mechanism. Premenopausal women with unipolar depression have significantly lower BMD because of stimulated bone cell metabolism with predomination of osteoresorption process

  10. Spin current

    CERN Document Server

    Valenzuela, Sergio O; Saitoh, Eiji; Kimura, Takashi

    2017-01-01

    Since the discovery of the giant magnetoresistance effect in magnetic multilayers in 1988, a new branch of physics and technology, called spin-electronics or spintronics, has emerged, where the flow of electrical charge as well as the flow of electron spin, the so-called “spin current,” are manipulated and controlled together. The physics of magnetism and the application of spin current have progressed in tandem with the nanofabrication technology of magnets and the engineering of interfaces and thin films. This book aims to provide an introduction and guide to the new physics and applications of spin current, with an emphasis on the interaction between spin and charge currents in magnetic nanostructures.

  11. Dependence of Interfacial Dzyaloshinskii-Moriya Interaction on Layer Thicknesses in Ta /Co -Fe -B /TaOx Heterostructures from Brillouin Light Scattering

    Science.gov (United States)

    Chaurasiya, Avinash Kumar; Choudhury, Samiran; Sinha, Jaivardhan; Barman, Anjan

    2018-01-01

    The interfacial Dzyaloshinskii-Moriya interaction (IDMI) has recently drawn extensive research interest due to its fundamental role in stabilizing chiral spin textures in ultrathin ferromagnets, which are suitable candidates for future magnetic-memory devices. Here, we explore the ferromagnetic and heavy-metal layer-thickness dependence of IDMI in technologically important Ta /Co20Fe60B20/TaOx heterostructures by measuring nonreciprocity in spin-wave frequency using the Brillouin light-scattering technique. The observed value of the IDMI constant agrees with that obtained from a separate measurement of in-plane angular dependence of frequency nonreciprocity, which is also in good agreement with the theory predicted by Cortes-Ortuno and Landeros. Linear scaling behavior of IDMI with the inverse of Co-Fe-B thicknesses suggests that IDMI originates primarily from the interface in these heterostructures, whereas we observe a weak dependence of Ta thickness on the strength of IDMI. Importantly, the observed value of the IDMI constant is reasonably large by a factor of 3 compared to annealed Ta /Co -Fe -B /MgO heterostructures. We propose that the observation of large IDMI is likely due to the absence of boron diffusion towards the Ta /Co -Fe -B interface as the heterostructures are as deposited. Our detailed investigation opens up a route to designing thin-film heterostructures with the tailored IDMI constant for controlling Skyrmion-based magnetic-memory devices.

  12. Novel electronic properties of a new MoS2/TiO2 heterostructure and potential applications in solar cells and photocatalysis

    Science.gov (United States)

    Li, Yanhua; Cai, Congzhong; Gu, Yonghong; Cheng, Wende; Xiong, Wen; Zhao, Chengjun

    2017-08-01

    The structural and electronic properties of two-dimensional (2D) MoS2/TiO2 heterostructure with a special configuration of Moiré pattern have been investigated for the first time using first-principles methods with van der Waals correction. It is found that the new van der Waals heterostructure is of a type-II band alignment between the MoS2 and TiO2 layers, and the electronic structures of monolayer MoS2 and 2D TiO2 are well retained in their respective layers due to a weak interlayer coupling, which suggests that the heterostructure may have potential applications in many fields such as photoelectric devices, photocatalysis, energy conversion and storage, etc. Meanwhile, the heterostructure can also provide an ideal platform of two-dimensional electron gas (2DEG) and two-dimensional hole gas (2DHG) for fundamental research such as spin Hall effect, etc. In addition, it is discovered that the corresponding MoS2/TiO2 superlattice also has similar electronic properties to MoS2/TiO2 bilayer heterostructure. Furthermore, two novel design schemes based on the MoS2/TiO2 heterostructure and superlattice are proposed for a solar cell and photocatalyst, respectively.

  13. Spin multiplicities

    Energy Technology Data Exchange (ETDEWEB)

    Curtright, T.L., E-mail: curtright@miami.edu [Department of Physics, University of Miami, Coral Gables, FL 33124-8046 (United States); Van Kortryk, T.S., E-mail: vankortryk@gmail.com [Department of Physics, University of Miami, Coral Gables, FL 33124-8046 (United States); High Energy Physics Division, Argonne National Laboratory, Argonne, IL 60439-4815 (United States); Zachos, C.K., E-mail: zachos@anl.gov [Department of Physics, University of Miami, Coral Gables, FL 33124-8046 (United States); High Energy Physics Division, Argonne National Laboratory, Argonne, IL 60439-4815 (United States)

    2017-02-05

    The number of times spin s appears in the Kronecker product of n spin j representations is computed, and the large n asymptotic behavior of the result is obtained. Applications are briefly sketched. - Highlights: • We give a self-contained derivation of the spin multiplicities that occur in n-fold tensor products of spin-j representations. • We make use of group characters, properties of special functions, and asymptotic analysis of integrals. • We emphasize patterns that arise when comparing different values of j, and asymptotic behavior for large n. • Our methods and results should be useful for various statistical and quantum information theory calculations.

  14. Tuning the band structure, magnetic and transport properties of the zigzag graphene nanoribbons/hexagonal boron nitride heterostructures by transverse electric field.

    Science.gov (United States)

    Ilyasov, V V; Meshi, B C; Nguyen, V C; Ershov, I V; Nguyen, D C

    2014-07-07

    The paper presents the results of ab initio study of the opportunities for tuning the band structure, magnetic and transport properties of zigzag graphene nanoribbon (8-ZGNR) on hexagonal boron nitride (h-BN(0001)) semiconductor heterostructure by transverse electric field (E(ext)). This study was performed within the framework of the density functional theory (DFT) using Grimme's (DFT-D2) scheme. We established the critical values of E(ext) for the 8-ZGNR/h-BN(0001) heterostructure, thereby providing for semiconductor-halfmetal transition in one of electron spin configurations. This study also showed that the degeneration in energy of the localized edge states is removed when E(ext) is applied. In ZGNR/h-BN (0001) heterostructure, value of the splitting energy was higher than one in ZGNRs without substrate. We determined the effect of low E(ext) applied to the 8-ZGNR/h-BN (0001) semiconductor heterostructure on the preserved local magnetic moment (LMM) (0.3μ(B)) of edge carbon atoms. The transport properties of the 8-ZGNR/h-BN(0001) semiconductor heterostructure can be controlled using E(ext). In particular, at a critical value of the positive potential, the electron mobility can increase to 7× 10(5) cm(2)/V s or remain at zero in the spin-up and spin-down electron subsystems, respectively. We established that magnetic moments (MMs), band gaps, and carrier mobility can be altered using E(ext). These abilities enable the use of 8-ZGNR/h-BN(0001) semiconductor heterostructure in spintronics.

  15. Quantum Information Processing by Electron Spin Resonance in a Transistor Structure

    Science.gov (United States)

    Yablonovitch, Eli

    2001-03-01

    Isolated electron spins in low temperature semiconductors are now recognized to have considerable potential for storing and manipulating quantum information. One of the great advantages of a spin in a semiconductor is that it can be embedded into a transistor structure, and it can thereby lend itself to large-scale integration of a quantum information processor. One essential element for spin-based quantum information processing is to be able to individually address the spins, or qubits, rotations. The electron spin resonance (ESR) electrons in a GaAs/AlGaAs heterostructure can be tuned by means of a gate voltage. The front and back gates of the heterostructure produce opposite g-factor shift, suggesting that electron g-factor is being electrostatically controlled by shifting the electron wave function from one epitaxial layer to another with different g-factors. We report our observations of gate-voltage tuned ESR in a two-dimensional electron system. We demonstrate that the electrostatic field of a gate can effectively adjust the weighting of the electron wave function between heterostructure layers of different composition producing a large g-factor change. We have monitored the ESR spin flips by means of the source/drain channel current, and conversely we have tuned the spin resonance frequency by means of the gate voltage. These are two of the elementary operations required in a quantum information processor.

  16. Emergent ultrafast phenomena in correlated oxides and heterostructures

    Science.gov (United States)

    Gandolfi, M.; Celardo, G. L.; Borgonovi, F.; Ferrini, G.; Avella, A.; Banfi, F.; Giannetti, C.

    2017-03-01

    The possibility of investigating the dynamics of solids on timescales faster than the thermalization of the internal degrees of freedom has disclosed novel non-equilibrium phenomena that have no counterpart at equilibrium. Transition metal oxides (TMOs) provide an interesting playground in which the correlations among the charges in the metal d-orbitals give rise to a wealth of intriguing electronic and thermodynamic properties involving the spin, charge, lattice and orbital orders. Furthermore, the physical properties of TMOs can be engineered at the atomic level, thus providing the platform to investigate the transport phenomena on timescales of the order of the intrinsic decoherence time of the charge excitations. Here, we review and discuss three paradigmatic examples of transient emerging properties that are expected to open new fields of research: (i) the creation of non-thermal magnetic states in spin-orbit Mott insulators; (ii) the possible exploitation of quantum paths for the transport and collection of charge excitations in heterostructures; (iii) the transient wave-like behavior of the temperature field in strongly anisotropic TMOs.

  17. Foreign-catalyst-free growth of InAs/InSb axial heterostructure nanowires on Si (111) by molecular-beam epitaxy

    Science.gov (United States)

    So, Hyok; Pan, Dong; Li, Lixia; Zhao, Jianhua

    2017-03-01

    Epitaxial high-quality InAs/InSb axial heterostructure nanowires are of great interest due to their distinct advantages in fundamental research as well as applications in semiconductor electronic and quantum devices. Currently, nearly all the growth of InAs/InSb axial heterostructure nanowires is assisted with foreign catalysts such as Au, and work on foreign-catalyst-free growth of InAs/InSb axial heterostructure nanowires is lacking. Here we report on the growth of InAs/InSb axial heterostructure nanowires on Si (111) substrates by molecular-beam epitaxy without using any foreign catalysts. The Sb/In beam equivalent pressure (BEP) ratio is found to have important influence on the heterostructure nanowire morphology, and InSb nanowires can be epitaxially grown on InAs nanowire stems with a hexagonal prism and nanosheet-like shapes when the Sb/In BEP ratio varies from 10 to 20. Transmission electron microscopy studies reveal that the InAs nanowire stems have a mixture of zincblende (ZB) and wurtzite (WZ) crystal structures, while InSb nanowire parts have a pure ZB crystal structure free of stacking faults. Composition analysis of axial heterostructure nanowires provides clear evidence that the InSb nanowires are epitaxially grown on InAs nanowires in an In self-assisted vapor-liquid-solid manner. This study paves a new route for growing narrow-gap semiconductor heterostructures with strong spin-orbit interaction for the study of topological states, and the growth manner presented here is expected to be used to grow other In-based axial heterostructure nanowires.

  18. 1D ferromagnetic edge contacts to 2D graphene/h-BN heterostructures

    Science.gov (United States)

    Karpiak, Bogdan; Dankert, André; Cummings, Aron W.; Power, Stephen R.; Roche, Stephan; Dash, Saroj P.

    2018-03-01

    We report the fabrication of one-dimensional (1D) ferromagnetic edge contacts to two-dimensional (2D) graphene/h-BN heterostructures. While aiming to study spin injection/detection with 1D edge contacts, a spurious magnetoresistance signal was observed, which is found to originate from the local Hall effect in graphene due to fringe fields from ferromagnetic edge contacts and in the presence of charge current spreading in the nonlocal measurement configuration. Such behavior has been confirmed by the absence of a Hanle signal and gate-dependent magnetoresistance measurements that reveal a change in sign of the signal for the electron- and hole-doped regimes, which is in contrast to the expected behavior of the spin signal. Calculations show that the contact-induced fringe fields are typically on the order of hundreds of mT, but can be reduced below 100 mT with careful optimization of the contact geometry. There may be an additional contribution from magnetoresistance effects due to tunneling anisotropy in the contacts, which needs further investigation. These studies are useful for optimization of spin injection and detection in 2D material heterostructures through 1D edge contacts.

  19. Vertical-Cavity In-plane Heterostructures: Physics and Applications

    DEFF Research Database (Denmark)

    Taghizadeh, Alireza; Mørk, Jesper; Chung, Il-Sug

    2015-01-01

    We show that the in-plane heterostructures realized in vertical cavities with high contrast grating(HCG) reflector enables exotic configurations of heterostructure and photonic wells. In photonic crystal heterostructures forming a photonic well, the property of a confined mode is determined by th...... to discuss the rich potential of this heterostructure as a platform for various physics studies and propose a system of two laterally coupled cavities which shows the breaking of parity-time symmetry as an example....

  20. Spin Electronics

    Science.gov (United States)

    2003-08-01

    spin resonance of rare earth and transition metal impurities in chalcopyrite semiconductors. They also have worked in diluted magnetic...past, the ferromagnetic injector had been a ferromagnetic metal or alloy containing 3d transition elements with fractional spin polarization of the...polarized carriers. There have been numerous attempts to inject transition metals or their alloys into semiconductors, either directly (Johnson and

  1. Cat scratches, not bites, are associated with unipolar depression - cross-sectional study

    Czech Academy of Sciences Publication Activity Database

    Flegr, J.; Hodný, Zdeněk

    2016-01-01

    Roč. 9, Jan (2016), č. článku 8. ISSN 1756-3305 R&D Projects: GA ČR(CZ) GA16-20958S Institutional support: RVO:68378050 Keywords : Toxoplasmosis * Unipolar depression * Injury * Major depression * Parasite * Bartonelosis Subject RIV: EB - Genetics ; Molecular Biology Impact factor: 3.080, year: 2016

  2. Sensory processing patterns, coping strategies, and quality of life among patients with unipolar and bipolar disorders

    Directory of Open Access Journals (Sweden)

    Batya Engel-Yeger

    2016-01-01

    Full Text Available Objective: To compare sensory processing, coping strategies, and quality of life (QoL in unipolar and bipolar patients; to examine correlations between sensory processing and QoL; and to investigate the relative contribution of sociodemographic characteristics, sensory processing, and coping strategies to the prediction of QoL. Methods: Two hundred sixty-seven participants, aged 16-85 years (53.6±15.7, of whom 157 had a diagnosis of unipolar major depressive disorder and 110 had bipolar disorder type I and type II, completed the Adolescent/Adult Sensory Profile, Coping Orientations to Problems Experienced, and 12-item Short-Form Health Survey version 2. The two groups were compared with multivariate analyses. Results: The unipolar and bipolar groups did not differ concerning sensory processing, coping strategies, or QoL. Sensory processing patterns correlated with QoL independently of mediation by coping strategies. Correlations between low registration, sensory sensitivity, sensation avoidance, and reduced QoL were found more frequently in unipolar patients than bipolar patients. Higher physical QoL was mainly predicted by lower age and lower sensory sensitivity, whereas higher mental QoL was mainly predicted by coping strategies. Conclusion: While age may predict physical QoL, coping strategies predict mental QoL. Future studies should further investigate the impact of sensory processing and coping strategies on patients’ QoL in order to enhance adaptive and functional behaviors related to affective disturbances.

  3. Sensory processing patterns, coping strategies, and quality of life among patients with unipolar and bipolar disorders.

    Science.gov (United States)

    Engel-Yeger, Batya; Gonda, Xenia; Muzio, Caterina; Rinosi, Giorgio; Pompili, Maurizio; Amore, Mario; Serafini, Gianluca

    2016-01-01

    To compare sensory processing, coping strategies, and quality of life (QoL) in unipolar and bipolar patients; to examine correlations between sensory processing and QoL; and to investigate the relative contribution of sociodemographic characteristics, sensory processing, and coping strategies to the prediction of QoL. Two hundred sixty-seven participants, aged 16-85 years (53.6±15.7), of whom 157 had a diagnosis of unipolar major depressive disorder and 110 had bipolar disorder type I and type II, completed the Adolescent/Adult Sensory Profile, Coping Orientations to Problems Experienced, and 12-item Short-Form Health Survey version 2. The two groups were compared with multivariate analyses. The unipolar and bipolar groups did not differ concerning sensory processing, coping strategies, or QoL. Sensory processing patterns correlated with QoL independently of mediation by coping strategies. Correlations between low registration, sensory sensitivity, sensation avoidance, and reduced QoL were found more frequently in unipolar patients than bipolar patients. Higher physical QoL was mainly predicted by lower age and lower sensory sensitivity, whereas higher mental QoL was mainly predicted by coping strategies. While age may predict physical QoL, coping strategies predict mental QoL. Future studies should further investigate the impact of sensory processing and coping strategies on patients' QoL in order to enhance adaptive and functional behaviors related to affective disturbances.

  4. Latent Bipolarity In Unipolar Depression: Experimental Findings, Conceptual Analysis And Implications For Treatment Strategies

    Directory of Open Access Journals (Sweden)

    Terziivanova Petya D.

    2014-12-01

    Full Text Available Introduction: Previous studies have suggested that the two opposite poles of psychomotor disturbances in unipolar depression (UD – retardation and agitation – require different treatment strategies as the psychomotor overactivation requires an augmentation of the antidepressant therapy with mood stabilizers and/or atypical antipsychotics.

  5. P2RX7: A bipolar and unipolar disorder candidate susceptibility gene?

    Science.gov (United States)

    Green, Elaine K; Grozeva, Detelina; Raybould, Rachel; Elvidge, Gareth; Macgregor, Stuart; Craig, Ian; Farmer, Anne; McGuffin, Peter; Forty, Liz; Jones, Lisa; Jones, Ian; O'Donovan, Mick C; Owen, Mike J; Kirov, George; Craddock, Nick

    2009-12-05

    The chromosomal region 12q24 has been previously implicated by linkage studies of both bipolar disorder and unipolar mood disorder and we have reported two pedigrees segregating both bipolar disorder and Darier's disease that show linkage across this region. The gene P2RX7 is located in this chromosomal region and has been recently reported as a susceptibility gene for bipolar disorder and unipolar depression. The non-synonymous SNP rs2230912 (resulting in amino-acid polymorphism Q460R) showed the strongest association and has been postulated to be pathogenically relevant. We have investigated this gene in a large UK case-control sample (bipolar I disorder N = 687, unipolar recurrent major depression N = 1,036, controls N = 1,204). Neither rs2230912 nor any of 8 other SNPs genotyped across P2RX7 was found to be associated with mood disorder in general, nor specifically with bipolar or unipolar disorder. Further, sequencing of our two chromosome 12-linked bipolar-Darier families showed no evidence of rare variants at P2RX7 that could explain the linkage. Our data do not provide support for rs2230912 or the other polymorphisms studied within the P2RX7 locus, being involved in susceptibility to mood disorders. 2009 Wiley-Liss, Inc.

  6. Severe Intellectual Disability: Systematic Review of the Prevalence and Nature of Presentation of Unipolar Depression

    Science.gov (United States)

    Walton, Catherine; Kerr, Mike

    2016-01-01

    Background: The diagnosis of depression in severe and profound intellectual disability is challenging. Without adequate skills in verbal self-expression, standardized diagnostic criteria cannot be used with confidence. The purpose of this systematic review was to investigate the assessment and diagnosis of unipolar depression in severe and…

  7. Enhanced Salt Removal by Unipolar Ion Conduction in Ion Concentration Polarization Desalination

    Science.gov (United States)

    Kwak, Rhokyun; Pham, Van Sang; Kim, Bumjoo; Chen, Lan; Han, Jongyoon

    2016-01-01

    Chloride ion, the majority salt in nature, is ∼52% faster than sodium ion (DNa+ = 1.33, DCl− = 2.03[10−9m2s−1]). Yet, current electrochemical desalination technologies (e.g. electrodialysis) rely on bipolar ion conduction, removing one pair of the cation and the anion simultaneously. Here, we demonstrate that novel ion concentration polarization desalination can enhance salt removal under a given current by implementing unipolar ion conduction: conducting only cations (or anions) with the unipolar ion exchange membrane stack. Combining theoretical analysis, experiment, and numerical modeling, we elucidate that this enhanced salt removal can shift current utilization (ratio between desalted ions and ions conducted through electrodes) and corresponding energy efficiency by the factor ∼(D− − D+)/(D− + D+). Specifically for desalting NaCl, this enhancement of unipolar cation conduction saves power consumption by ∼50% in overlimiting regime, compared with conventional electrodialysis. Recognizing and utilizing differences between unipolar and bipolar ion conductions have significant implications not only on electromembrane desalination, but also energy harvesting applications (e.g. reverse electrodialysis). PMID:27158057

  8. Designing Context-Aware Cognitive Behavioral Therapy for Unipolar and Bipolar Disorders

    DEFF Research Database (Denmark)

    Bardram, Jakob Eyvind; Frost, Mads; Tuxen, Nanna

    2016-01-01

    This position paper presents our preliminary design of context-aware cognitive behavioral therapy for unipolar and bipolar disorders. We report on the background for this study and the methods applied in the ongoing design process. The paper ends by presenting and discussing different design opti...

  9. Comparison between Continuous Bipolar and Unipolar Ratings of the Myers-Briggs Type Indicator.

    Science.gov (United States)

    Tzeng, Oliver C. S.; And Others

    1991-01-01

    Measurement properties of two response formats (bipolar and unipolar ratings) in personality assessment were compared using data from 135 college students taking the Myers-Briggs Type Indicator (MBTI). Factorial validity and construct validity of the MBTI were supported. Reasons why the bipolar method is preferable are discussed. (SLD)

  10. Designing Context-Aware Cognitive Behavioral Therapy for Unipolar and Bipolar Disorders

    DEFF Research Database (Denmark)

    Bardram, Jakob Eyvind; Frost, Mads; Tuxen, Nanna

    2016-01-01

    This position paper presents our preliminary design of context-aware cognitive behavioral therapy for unipolar and bipolar disorders. We report on the background for this study and the methods applied in the ongoing design process. The paper ends by presenting and discussing different design...

  11. Diminished Effort on a Progressive Ratio Task in Both Unipolar and Bipolar Depression

    Science.gov (United States)

    Hershenberg, Rachel; Satterthwaite, Theodore D.; Daldal, Aylin; Katchmar, Natalie; Moore, Tyler M.; Kable, Joseph W.; Wolf, Daniel H.

    2016-01-01

    Background Amotivation, or decisional anhedonia, is a prominent and disabling feature of depression. However, this aspect of depression remains understudied, and no prior work has applied objective laboratory tests of motivation in both unipolar and bipolar depression. Methods We assessed motivation deficits using a Progressive Ratio Task (PRT) that indexes willingness to exert effort for monetary reward. The PRT was administered to 96 adults ages 18–60 including 25 participants with a current episode of unipolar depression, 28 with bipolar disorder (current episode depressed), and 43 controls without any lifetime history of Axis I psychiatric disorders. Results Depressed participants exhibited significantly lower motivation than control participants as objectively defined by progressive ratio breakpoints. Both the unipolar and bipolar groups were lower than controls but did not differ from each other. Limitations Medication use differed across groups, and we did not have a separate control task to measure psychomotor activity; however neither medication effects or psychomotor slowing are likely to explain our findings. Conclusions Our study fills an important gap in the literature by providing evidence that diminished effort on the PRT is present across depressed patients who experience either unipolar or bipolar depression. This adds to growing evidence for shared mechanisms of reward and motivation dysfunction, and highlights the importance of improving the assessment and treatment of motivation deficits across the mood disorders spectrum. PMID:26919058

  12. Spin glasses

    CERN Document Server

    Bovier, Anton

    2007-01-01

    Spin glass theory is going through a stunning period of progress while finding exciting new applications in areas beyond theoretical physics, in particular in combinatorics and computer science. This collection of state-of-the-art review papers written by leading experts in the field covers the topic from a wide variety of angles. The topics covered are mean field spin glasses, including a pedagogical account of Talagrand's proof of the Parisi solution, short range spin glasses, emphasizing the open problem of the relevance of the mean-field theory for lattice models, and the dynamics of spin glasses, in particular the problem of ageing in mean field models. The book will serve as a concise introduction to the state of the art of spin glass theory, usefull to both graduate students and young researchers, as well as to anyone curious to know what is going on in this exciting area of mathematical physics.

  13. Manganite/Cuprate Superlattice as Artificial Reentrant Spin Glass

    KAUST Repository

    Ding, Junfeng

    2016-05-04

    Emerging physical phenomena at the unit-cell-controlled interfaces of transition-metal oxides have attracted lots of interest because of the rich physics and application opportunities. This work reports a reentrant spin glass behavior with strong magnetic memory effect discovered in oxide heterostructures composed of ultrathin manganite La0.7Sr0.3MnO3 (LSMO) and cuprate La2CuO4 (LCO) layers. These heterostructures are featured with enhanced ferromagnetism before entering the spin glass state: a Curie temperature of 246 K is observed in the superlattice with six-unit-cell LSMO layers, while the reference LSMO film with the same thickness shows much weaker magnetism. Furthermore, an insulator-metal transition emerges at the Curie temperature, and below the freezing temperature the superlattices can be considered as a glassy ferromagnetic insulator. These experimental results are closely related to the interfacial spin reconstruction revealed by the first-principles calculations, and the dependence of the reentrant spin glass behavior on the LSMO layer thickness is in line with the general phase diagram of a spin system derived from the infinite-range SK model. The results of this work underscore the manganite/cuprate superlattices as a versatile platform of creating artificial materials with tailored interfacial spin coupling and physical properties. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  14. The effects of interfacial exchange coupling in Fe/ErFeO3 heterostructures

    Science.gov (United States)

    Tang, J.; Ke, Y. J.; He, W.; Zhang, X. Q.; Zhang, Y. S.; Zhang, W.; Li, Y.; Ahmad, S. S.; Cheng, Z. H.

    2017-05-01

    Exploring exchange bias in ferromagnetic (FM)/antiferromagnetic (AFM) heterostructures is vital for both fundamental magnetism and practical application. However, in the case of conventional FM/AFM systems, the essential field cooling process above the Néel temperature of AFM materials hinders their application if the Néel temperature is far higher than room-temperature. Here, we report the effects of interfacial exchange coupling in Fe/ErFeO3 heterostructures. The magnetic-field-induced switchable exchange bias, originating from the AFM exchange coupling between Fe film and Dzyaloshinskii-Moriya-interaction-induced net moment of ErFeO3 along c axis, is successfully achieved without field cooling or in-field growth process of AFM. Different from the most previous pinning layer using a hard FM or traditional AFM, ErFeO3 pinning layer has the advantages of both the magnetic field sensitivity (~780 Oe) and ultrahigh dynamic frequency. In addition, although Fe film is polycrystalline, it exhibits a strong uniaxial magnetic anisotropy resulted from the so-called ‘spin-flop-coupling effect’, i.e. the magnetic coupling between Fe film and the compensated G-type AFM spins of EFO along a axis. Interestingly, the exchange bias field and asymmetric switching field offer entirely different information about the asymmetry of magnetization reversal near hard axis. The asymmetric switching field is further proved to be an effective measure to determine the weak unidirectional magnetic anisotropy for film with nearly 180° domain wall displacement. Our experimental results provide a practical method to establish room-temperature exchange bias in FM/G-type AFM without field cooling. Furthermore, the magnetic-field-induced switchable exchange-bias, the spin-flop coupling effect and the angular dependent asymmetry of magnetization reversal in the vicinity of hard axis in Fe/ErFeO3 heterostructures may provide new insights on the interfacial exchange coupling in FM/AFM systems.

  15. Spin wave generation by surface acoustic waves

    Science.gov (United States)

    Li, Xu; Labanowski, Dominic; Salahuddin, Sayeef; Lynch, Christopher S.

    2017-07-01

    Surface acoustic waves (SAW) on piezoelectric substrates can excite spin wave resonance (SWR) in magnetostrictive films through magnetoelastic coupling. This acoustically driven SWR enables the excitation of a single spin wave mode with an in-plane wave vector k matched to the magnetoelastic wave vector. A 2D frequency domain finite element model is presented that fully couples elastodynamics, micromagnetics, and piezoelectricity with interface spin pumping effects taken into account. It is used to simulate SAW driven SWR on a ferromagnetic and piezoelectric heterostructure device with an interdigital transducer configuration. These results, for the first time, present the spatial distribution of magnetization components that, together with elastic wave, exponentially decays along the propagation direction due to magnetic damping. The results also show that the system transmission rate S21(dB) can be tuned by both an external bias field and the SAW wavevector. Acoustic spin pumping at magnetic film/normal metal interface leads to damping enhancement in magnetic films that decreases the energy absorption rate from elastic energy. This weakened interaction between the magnetic energy and elastic energy leads to a lower evanescence rate of the SAW that results in a longer distance propagation. With strong magnetoelastic coupling, the SAW driven spin wave is able to propagate up to 1200 μm. The results give a quantitative indication of the acoustic spin pumping contribution to linewidth broadening.

  16. The Relationship of Childhood Abuse and Neglect with Suicide Attempts in an Adult Unipolar Depression Sample.

    Science.gov (United States)

    Yildirim, Feride; Küçükgöncü, Suat; Beştepe, Engin Emrem; Yildirim, Murat Serkan

    2014-06-01

    Unipolar depression is an important psychiatric disorder that leads to an increased risk of suicide. However, not all depression patients attempt suicide. This reflects the presence of other factors that may be related to suicide other than the sole presence of psychopathology. Drawing upon the clinical evidence linking childhood abuse and neglect experiences with suicide; this study aimed at investigating the relationship of childhood abuse and neglect experiences with suicide attempts in patients with unipolar depression. One hundred six unipolar depressed patients between the ages of 18 and 65 were included in the study. Patients with comorbid psychiatric disorders, neurological disorders, alcohol-substance abuse problems, and a Beck Depression Inventory (BDI) score of Childhood Trauma Questionnaire (CTQ-28), State-Trait Anger Expression Inventory (STAXI), and the Suicide Behavior Questionnaire (SBQ) were administered to all patients. Suicidal and non-suicidal cases were determined according to clinic interviews and the patients' responses in the SBQ. Sixty-four patients have previously attempted suicide. Although there was no significant difference between unipolar depression patients with a history of suicide attempts and patients with no history of suicide attempts in terms of average age, education and marital status, however, female/male ratio in the former group was determined to be significantly higher. BDI, STAXI continuous anger and outward anger average scores, and average CTQ-28 emotional abuse, physical abuse and total scores were significantly higher in the group with a history of suicide attempts. The predictors of suicide attempts were higher BDI and CTQ-28 physical abuse scores and female gender. The predictors for average SBQ scores were determined as higher BDI, CTQ-28 sexual abuse, and STAXI outward anger and continuous anger scores. Childhood physical and sexual abuse experiences are important factors in evaluating the presence of suicide

  17. Psychopathological characteristics of bipolar and unipolar depression - potential indicators of bipolarity.

    Science.gov (United States)

    Motovsky, Branislav; Pecenak, Jan

    2013-03-01

    Establishing whether a depressive episode is part of a unipolar or bipolar disorder is essential for treatment planning. Over recent years, a growing number of publications have discussed psychopathological characteristics that might serve as indicators of bipolarity in patients with a history of depression dominated by unipolar symptoms. Our primary aim was to verify the adequacy of these indicators in contributing to a precise diagnosis in everyday clinical practice. We investigated 104 patients diagnosed with major depressive episode at the time of examination. 52 patients had major depressive disorder and 52 patients had bipolar disorder. The patients were then assessed for the presence of potential bipolarity indicators: psychomotor slowing, self-view (self-blaming, feelings of worthlessness), hypersomnia, increased appetite, leaden paralysis/loss of physical energy, weight increase, interpersonal sensitivity, and early morning insomnia, using the Inventory of Depressive Symptomatology. We analysed the correlations between these indicators and the presence of unipolar or bipolar affective disorder. Psychomotor slowing, self-blaming/feelings of worthlessness, increased appetite, leaden paralysis/loss of physical energy, and weight increase were significantly more frequent in bipolar depression than in unipolar depression (p<0.05). Early morning insomnia was significantly more frequent in unipolar depression (p<0.05). There was no statistically significant correlation between hypersomnia or interpersonal sensitivity and either of the affective disorders. It would be worthwhile identifying the relative importance of clinical indicators for probable BP in large-scale prospective studies. These would contribute to the better diagnostic assessment of major depressive episodes and therapeutic decision-making.

  18. Manipulating the L-valley electron g factor in Si-Ge heterostructures

    Science.gov (United States)

    Baron, F. A.; Kiselev, A. A.; Robinson, H. D.; Kim, K. W.; Wang, K. L.; Yablonovitch, E.

    2003-11-01

    The Zeeman effect for the L valley conduction band electrons in SiGe heterostructures is considered. A detailed calculation of the electron g tensor is performed in the framework of a relevant kṡp model, developed specifically for the L point of the Brillouin zone. Electrons at the L point are considered under the influence of the different crystallographic orientations, alloy composition, quantum confinement, strain, and electric field, whose interplay causes a considerable deviation of the g tensor components from their bulk values. Our result strongly suggests that the SiGe-based quantum wells are a promising choice for the g tensor engineering for spin manipulation.

  19. In-plane light-hole g factor in strained cubic heterostructures

    Science.gov (United States)

    Kiselev, A. A.; Kim, K. W.; Yablonovitch, E.

    2001-09-01

    In the context of a proposed design of a solid-state receiver for quantum communications, we consider the Zeeman splitting of the light-hole states in strained cubic heterostructures with an in-plane external magnetic field. The choice of interband optical transitions that allows coherent transfer of photon polarization to electron spin suggests that the magnitude of corresponding g factor component will be a critically important quantity for the success of such devices. Our approach allows a straightforward calculation of this parameter and incorporates the quantum confinement, heterolayers composition, and strain effects on the g factor.

  20. Scanning probe microscopy investigation of complex-oxide heterostructures

    Science.gov (United States)

    Bi, Feng

    Advances in the growth of precisely tailored complex-oxide heterostructures have led to new emergent behavior and associated discoveries. One of the most successful examples consists of an ultrathin layer of LaAlO 3 (LAO) deposited on TiO2-terminated SrTiO3 (STO), where a high mobility quasi-two dimensional electron liquid (2DEL) is formed at the interface. Such 2DEL demonstrates a variety of novel properties, including field tunable metal-insulator transition, superconductivity, strong spin-orbit coupling, magnetic and ferroelectric like behavior. Particularly, for 3-unit-cell (3 u.c.) LAO/STO heterostructures, it was demonstrated that a conductive atomic force microscope (c-AFM) tip can be used to "write" or "erase" nanoscale conducting channels at the interface, making LAO/STO a highly flexible platform to fabricate novel nanoelectronics. This thesis is focused on scanning probe microscopy studies of LAO/STO properties. We investigate the mechanism of c-AFM lithography over 3 u.c. LAO/STO in controlled ambient conditions by using a vacuum AFM, and find that the water molecules dissociated on the LAO surface play a critical role during the c-AFM lithography process. We also perform electro-mechanical response measurements over top-gated LAO/STO devices. Simultaneous piezoresponse force microscopy (PFM) and capacitance measurements reveal a correlation between LAO lattice distortion and interfacial carrier density, which suggests that PFM could not only serve as a powerful tool to map the carrier density at the interface but also provide insight into previously reported frequency dependence of capacitance enhancement of top-gated LAO/STO structures. To study magnetism at the LAO/STO interface, magnetic force microscopy (MFM) and magnetoelectric force microscopy (MeFM) are carried out to search for magnetic signatures that depend on the carrier density at the interface. Results demonstrate an electronicallycontrolled ferromagnetic phase on top-gated LAO

  1. Spin Orbit coupling and Anomalous Josephson effect in Nanowires

    OpenAIRE

    Campagnano, G.; Lucignano, P.; Giuliano, D.; Tagliacozzo, A.

    2014-01-01

    A superconductor-semiconducting nanowire-superconductor heterostructure in the presence of spin orbit coupling and magnetic field can support a supercurrent even in the absence of phase difference between the superconducting electrodes. We investigate this phenomenon, the anomalous Josephson effect, employing a model capable of describing many bands in the normal region. We discuss geometrical and symmetry conditions required to have finite anomalous supercurrent and in particular we show tha...

  2. Collective Behavior of a Spin-Aligned Gas of Interwell Excitons in Double Quantum Wells

    DEFF Research Database (Denmark)

    Larionov, A. V.; Bayer, M.; Hvam, Jørn Märcher

    2005-01-01

    The kinetics of a spin-aligned gas of interwell excitons in GaAs/AlGaAs double quantum wells (n–i–n heterostructure) is studied. The temperature dependence of the spin relaxation time for excitons, in which a photoexcited electron and hole are spatially separated between two adjacent quantum well...... is associated with indirect evidence of the coherence of the collective phase of interwell excitons at temperatures below the critical value....

  3. Spin-dependent tunneling in modulated structures of (Ga,Mn)As

    OpenAIRE

    Sankowski, P.; Kacman, P.; Majewski, J. A.; Dietl, T.

    2006-01-01

    A model of coherent tunneling, which combines multi-orbital tight-binding approximation with Landauer-B\\"uttiker formalism, is developed and applied to all-semiconductor heterostructures containing (Ga,Mn)As ferromagnetic layers. A comparison of theoretical predictions and experimental results on spin-dependent Zener tunneling, tunneling magnetoresistance (TMR), and anisotropic magnetoresistance (TAMR) is presented. The dependence of spin current on carrier density, magnetization orientation,...

  4. Terahertz semiconductor-heterostructure laser.

    Science.gov (United States)

    Köhler, Rüdeger; Tredicucci, Alessandro; Beltram, Fabio; Beere, Harvey E; Linfield, Edmund H; Davies, A Giles; Ritchie, David A; Iotti, Rita C; Rossi, Fausto

    2002-05-09

    Semiconductor devices have become indispensable for generating electromagnetic radiation in everyday applications. Visible and infrared diode lasers are at the core of information technology, and at the other end of the spectrum, microwave and radio-frequency emitters enable wireless communications. But the terahertz region (1-10 THz; 1 THz = 10(12) Hz) between these ranges has remained largely underdeveloped, despite the identification of various possible applications--for example, chemical detection, astronomy and medical imaging. Progress in this area has been hampered by the lack of compact, low-consumption, solid-state terahertz sources. Here we report a monolithic terahertz injection laser that is based on interminiband transitions in the conduction band of a semiconductor (GaAs/AlGaAs) heterostructure. The prototype demonstrated emits a single mode at 4.4 THz, and already shows high output powers of more than 2 mW with low threshold current densities of about a few hundred A cm(-2) up to 50 K. These results are very promising for extending the present laser concept to continuous-wave and high-temperature operation, which would lead to implementation in practical photonic systems.

  5. Spin and charge transport in a gated two dimensional electron gas

    NARCIS (Netherlands)

    Lerescu, Alexandru Ionut

    2007-01-01

    The work presented in this thesis is centered around the idea of how one can inject, transport and detect the electron's spin in a two dimensional electron gas (a semiconductor heterostructure). Metal based spintronic devices have been established to be the easy way to implement spintronic concepts

  6. Semitransparent anisotropic and spin Hall magnetoresistance sensor enabled by spin-orbit torque biasing

    Science.gov (United States)

    Yang, Yumeng; Xu, Yanjun; Xie, Hang; Xu, Baoxi; Wu, Yihong

    2017-07-01

    We demonstrate an ultrathin and semitransparent anisotropic and spin Hall magnetoresistance sensor based on NiFe/Pt heterostructures. The use of a spin-orbit torque effective field for transverse biasing allows us to reduce the total thickness of the sensors down to 3-4 nm, thereby leading to the semitransparency. Despite the extremely simple design, the spin-orbit torque effective field biased NiFe/Pt sensor exhibits levels of linearity and sensitivity comparable to those of sensors using more complex linearization schemes. In a proof-of-concept design using a full Wheatstone bridge comprising four sensing elements, we obtained a sensitivity up to 202.9 mΩ Oe-1, a linearity error below 5%, and a detection limit down to 20 nT. The transmittance of the sensor is over 50% in the visible range.

  7. Spin-orbit-induced spin splittings in polar transition metal dichalcogenide monolayers

    KAUST Repository

    Cheng, Yingchun

    2013-06-01

    The Rashba effect in quasi two-dimensional materials, such as noble metal surfaces and semiconductor heterostructures, has been investigated extensively, while interest in real two-dimensional systems has just emerged with the discovery of graphene. We present ab initio electronic structure, phonon, and molecular-dynamics calculations to study the structural stability and spin-orbit-induced spin splitting in the transition metal dichalcogenide monolayers MXY (M = Mo, W and X, Y = S, Se, Te). In contrast to the non-polar systems with X = Y, in the polar systems with X ≠ Y the Rashba splitting at the Γ-point for the uppermost valence band is caused by the broken mirror symmetry. An enhancement of the splitting can be achieved by increasing the spin-orbit coupling and/or the potential gradient. © Copyright EPLA, 2013.

  8. TOPICAL REVIEW: Spin current, spin accumulation and spin Hall effect

    Directory of Open Access Journals (Sweden)

    Saburo Takahashi and Sadamichi Maekawa

    2008-01-01

    Full Text Available Nonlocal spin transport in nanostructured devices with ferromagnetic injector (F1 and detector (F2 electrodes connected to a normal conductor (N is studied. We reveal how the spin transport depends on interface resistance, electrode resistance, spin polarization and spin diffusion length, and obtain the conditions for efficient spin injection, spin accumulation and spin current in the device. It is demonstrated that the spin Hall effect is caused by spin–orbit scattering in nonmagnetic conductors and gives rise to the conversion between spin and charge currents in a nonlocal device. A method of evaluating spin–orbit coupling in nonmagnetic metals is proposed.

  9. Spin electronics

    CERN Document Server

    Buhrman, Robert; Daughton, James; Molnár, Stephan; Roukes, Michael

    2004-01-01

    This report is a comparative review of spin electronics ("spintronics") research and development activities in the United States, Japan, and Western Europe conducted by a panel of leading U.S. experts in the field. It covers materials, fabrication and characterization of magnetic nanostructures, magnetism and spin control in magnetic nanostructures, magneto-optical properties of semiconductors, and magnetoelectronics and devices. The panel's conclusions are based on a literature review and a series of site visits to leading spin electronics research centers in Japan and Western Europe. The panel found that Japan is clearly the world leader in new material synthesis and characterization; it is also a leader in magneto-optical properties of semiconductor devices. Europe is strong in theory pertaining to spin electronics, including injection device structures such as tunneling devices, and band structure predictions of materials properties, and in development of magnetic semiconductors and semiconductor heterost...

  10. Manipulation of magnetic exchange in iridate heterostructures

    Science.gov (United States)

    Meyers, D.; Fabbris, G.; Yin, Weiguo; Casa, D.; Cao, Yue; Hao, Lin; Schmitt, T.; Liu, Jian; Dean, M. P. M.

    Artificial layering of disparate materials into superlattices is an emerging method that promises unparalleled versatility in accessing ground states unavailable to bulk synthesis. Heterostructures composed of paramagnetic, metallic SrIrO3 interspaced with band insulating SrTiO3 were found to host a canted antiferromagnetic ground state, mirroring the Ruddlesen-Popper series iridates with enhanced tunability. We investigate the magnetic excitation spectrum of these artificial systems using resonant inelastic x-ray scattering and directly infer the interlayer and intralayer magnetic exchange interactions. Understanding how interfacial effects modify magnetic interactions is a vital prerequisite for efforts to controllably target different ground states within complex oxide-heterostructures.

  11. Partial spin polarization of a conductance in a bi-layer In0.52 Al0.48 As / In0.53 Ga0.47 As heterostructure based nanowire for the rectangular and the smooth lateral confinement potentials

    Science.gov (United States)

    Chwiej, T.

    2016-03-01

    We simulate the electron transport in a vertical bi-layer nanowire in order to study an influence of the lateral confinement's shape on a spin polarization of wire's conductance. The active part of considered quantum wire constitutes a double inverted heterojunction In0.52 Al0.48 As /In0.53 Ga0.47 As which nanostructure can be fabricated in molecular beam epitaxy process while the lateral confinement potential can be finally formed by means of cleaved overgrowth or surface oxidization methods giving the desired rectangular and smooth lateral confinement. In calculations we take into account interaction between charge carriers using DFT within local spin density approximation. We show that if the magnetic field is perpendicular to the wire axis, the pseudogaps are opened in energy dispersion relation E (k) what in conjunction with spin Zeeman shift of spin-up and spin-down subbands may enhance the spin polarization of conductance with reference to a single layer wire. For nanowire with rectangular lateral confinement potential we found that the electron density has two maximums localized at wire edges in each layers. This modificates strongly all magnetosubbands giving up to four energy minimums in lowest subband and considerably diminishes widths of pseudogaps what translates into low maximal spin polarization of conductance, not exceeding 40%. This drawback is absent in wire with smooth lateral confinement. However, in order to gain a large spin polarization simultaneous tuning of magnetic field as well as the Fermi energies in both layers of nanowire are required.

  12. Topological phases in superconductor-noncollinear magnet interfaces with strong spin-orbit coupling

    Energy Technology Data Exchange (ETDEWEB)

    Menke, H.; Schnyder, A.P. [Max-Planck-Institut fuer Festkoerperforschung, Heisenbergstrasse 1, 70569 Stuttgart (Germany); Toews, A. [Max-Planck-Institut fuer Festkoerperforschung, Heisenbergstrasse 1, 70569 Stuttgart (Germany); Quantum Matter Institute, University of British Columbia, Vancouver, BC (Canada)

    2016-07-01

    Majorana fermions are predicted to emerge at interfaces between conventional s-wave superconductors and non-collinear magnets. In these heterostructures, the spin moments of the non-collinear magnet induce a low-energy band of Shiba bound states in the superconductor. Depending on the type of order of the magnet, the band structure of these bound states can be topologically nontrivial. Thus far, research has focused on systems where the influence of spin-orbit coupling can be neglected. Here, we explore the interplay between non-collinear (or non-coplanar) spin textures and Rashba-type spin-orbit interaction. This situation is realized, for example, in heterostructures between helical magnets and heavy elemental superconductors, such as Pb. Using a unitary transformation in spin space, we show that the effects of Rashba-type spin-orbit coupling are equivalent to the effects of the non-collinear spin texture of the helical magnet. We explore the topological phase diagram as a function of spin-orbit coupling, spin texture, and chemical potential, and find many interesting topological phases, such as p{sub x}-, (p{sub x} + p{sub y})-, and (p{sub x} + i p{sub y})-wave states. Conditions for the formation and the nature of Majorana edge channels are examined. Furthermore, we study the topological edge currents of these phases.

  13. Spin pumping through a topological insulator probed by x-ray detected ferromagnetic resonance

    Energy Technology Data Exchange (ETDEWEB)

    Figueroa, A.I., E-mail: aifigueg@gmail.com [Magnetic Spectroscopy Group, Diamond Light Source, Didcot OX11 0DE (United Kingdom); Baker, A.A. [Magnetic Spectroscopy Group, Diamond Light Source, Didcot OX11 0DE (United Kingdom); Department of Physics, Clarendon Laboratory, University of Oxford, Oxford OX1 3PU (United Kingdom); Collins-McIntyre, L.J.; Hesjedal, T. [Department of Physics, Clarendon Laboratory, University of Oxford, Oxford OX1 3PU (United Kingdom); Laan, G. van der [Magnetic Spectroscopy Group, Diamond Light Source, Didcot OX11 0DE (United Kingdom)

    2016-02-15

    In the field of spintronics, the generation of a pure spin current (without macroscopic charge flow) through spin pumping of a ferromagnetic (FM) layer opens up the perspective of a new generation of dissipation-less devices. Microwave driven ferromagnetic resonance (FMR) can generate a pure spin current that enters adjacent layers, allowing for both magnetization reversal (through spin-transfer torque) and to probe spin coherence in non-magnetic materials. However, standard FMR is unable to probe multilayer dynamics directly, since the measurement averages over the contributions from the whole system. The synchrotron radiation-based technique of x-ray detected FMR (XFMR) offers an elegant solution to this drawback, giving access to element-, site-, and layer-specific dynamical measurements in heterostructures. In this work, we show how XFMR has provided unique information to understand spin pumping and spin transfer torque effects through a topological insulator (TI) layer in a pseudo-spin valve heterostructure. We demonstrate that TIs function as efficient spin sinks, while also allowing a limited dynamic coupling between ferromagnetic layers. These results shed new light on the spin dynamics of this novel class of materials, and suggest future directions for the development of room temperature TI-based spintronics. - Highlights: • X-ray detected ferromagnetic resonance is used to study the spin pumping phenomenon. • We show a powerful way to get information of spin transfer between magnetic layers. • We observe spin pumping through a topological insulators at room temperature. • Topological insulators function as efficient spin sinks.

  14. Magnetic and electronic properties of Fe3O4/graphene heterostructures: First principles perspective

    KAUST Repository

    Mi, Wenbo

    2013-02-27

    Magnetic and electronic properties of Fe3O4(111)/graphene heterostructures are investigated by first principles calculations. Different structural models have been considered, which differ in the interface termination of Fe3O4(111) surface with respect to the same monolayer graphene. In three models, the magnetic moment of Fe(A) has a major change due to less O atoms surrounding Fe(A) atoms than Fe(B). Magnetic moment is enhanced by 8.5%, 18.5%, and 8.7% for models (a), (b), and (c), respectively. Furthermore, the spin polarization of models (a) and (c) is lowered due to the simultaneous occurrence of density of states of spin-up Fe(A) and spin-down Fe(B) at Fermi lever. The spin polarization of model (b) remains the same as that of bulk Fe3O4. Our results suggest that different interface terminations and Fe(A) play an important role in determining the magnetism strength and spin polarization.

  15. Proximity Effects in Bilayer Graphene on Monolayer WSe2 : Field-Effect Spin Valley Locking, Spin-Orbit Valve, and Spin Transistor

    Science.gov (United States)

    Gmitra, Martin; Fabian, Jaroslav

    2017-10-01

    Proximity orbital and spin-orbit effects of bilayer graphene on monolayer WSe2 are investigated from first principles. We find that the built-in electric field induces an orbital band gap of about 10 meV in bilayer graphene. Remarkably, the proximity spin-orbit splitting for holes is 2 orders of magnitude—the spin-orbit splitting of the valence band at K is about 2 meV—more than for electrons. Effectively, holes experience spin valley locking due to the strong proximity of the lower graphene layer to WSe2 . However, applying an external transverse electric field of some 1 V /nm , countering the built-in field of the heterostructure, completely reverses this effect and allows, instead of holes, electrons to be spin valley locked with 2 meV spin-orbit splitting. Such a behavior constitutes a highly efficient field-effect spin-orbit valve, making bilayer graphene on WSe2 a potential platform for a field-effect spin transistor.

  16. Topological Spin Textures in Confined Geometries

    Science.gov (United States)

    Zang, Jiadong

    The magnetic skyrmion is a nanostructured spin texture stabilized by the spin-orbital coupling. Its nontrivial topology enables unique dynamical property and thermal stability, which give out promise on future magnetic memory devise. However, to enable its applications, it is essential to understand the skyrmion properties in confined geometries and tackle key challenges including the creation and detection of skyrmions, preferably without magnetic fields. In this talk, I will present our recent theory-experiment collaboration results, covering studies of skyrmions in nanoribbon, nanodisk, and nanowires. Zero field skyrmions and their polarization switch will be discussed. New skyrmion materials and new topological textures in helimagnet heterostructures will be presented. This work is supported by the Grant DE-SC0016424 funded by the U.S. Department of Energy, Office of Science.

  17. Electron refrigeration in hybrid structures with spin-split superconductors

    Science.gov (United States)

    Rouco, M.; Heikkilä, T. T.; Bergeret, F. S.

    2018-01-01

    Electron tunneling between superconductors and normal metals has been used for an efficient refrigeration of electrons in the latter. Such cooling is a nonlinear effect and usually requires a large voltage. Here we study the electron cooling in heterostructures based on superconductors with a spin-splitting field coupled to normal metals via spin-filtering barriers. The cooling power shows a linear term in the applied voltage. This improves the coefficient of performance of electron refrigeration in the normal metal by shifting its optimum cooling to lower voltage, and also allows for cooling the spin-split superconductor by reverting the sign of the voltage. We also show how tunnel coupling spin-split superconductors with regular ones allows for a highly efficient refrigeration of the latter.

  18. Cognitive impairment in the remitted state of unipolar depressive disorder: A systematic review

    DEFF Research Database (Denmark)

    Hasselbalch, Bo Jacob; Knorr, Ulla; Kessing, Lars Vedel

    2010-01-01

    BACKGROUND: It is unclear whether cognitive impairment is prevalent in the remitted state of unipolar disorder. AIM: To evaluate whether cognitive function is impaired in the remitted state in patients with unipolar depression compared with healthy control individuals, and to investigate...... in relation to psychosocial function, quality of life and risk of recurrence and to assess the effect of treatment intervention on cognitive function....... the association to prior course of illness, i.e. the number, duration and severity of prior depressive episodes. METHOD: Systematic search on existing on-line databases and hand-search of original published papers. RESULTS: A total of 11 studies fulfilled the selection criteria and were included in the review...

  19. Cognitive styles and life events interact to predict bipolar and unipolar symptomatology.

    Science.gov (United States)

    Reilly-Harrington, N A; Alloy, L B; Fresco, D M; Whitehouse, W G

    1999-11-01

    This study examined the interaction of cognitive style (as assessed self-report and information-processing battery) and stressful life events in predicting the clinician-rated depressive and manic symptomatology of participants with Research Diagnostic Criteria lifetime diagnoses of bipolar disorder (n = 49), unipolar depression (n = 97), or no lifetime diagnosis (n = 23). Bipolar and unipolar participants' attributional styles, dysfunctional attitudes, and negative self-referent information processing as assessed at Time 1 interacted significantly with the number of negative life events that occurred between Times 1 and 2 to predict increases in depressive symptoms from Time 1 to Time 2. Within the bipolar group, participants' Time 1 attributional styles and dysfunctional attitudes interacted significantly, and their self-referent information processing interacted marginally, with intervening life events to predict increases in manic symptoms from Time 1 to Time 2. These findings provide support for the applicability of cognitive vulnerability-stress theories of depression to bipolar spectrum disorders.

  20. 1/f Noise Scaling Analysis in Unipolar-Type Organic Nanocomposite Resistive Memory.

    Science.gov (United States)

    Song, Younggul; Jeong, Hyunhak; Jang, Jingon; Kim, Tae-Young; Yoo, Daekyoung; Kim, Youngrok; Jeong, Heejun; Lee, Takhee

    2015-07-28

    We studied noise characteristics of a nanocomposite of polyimide (PI) and phenyl-C61-butyric acid methyl ester (PCBM) (denoted as PI:PCBM), a composite for the organic nonvolatile resistive memory material. The current fluctuations were investigated over a bias range that covers various intermediate resistive states and negative differential resistance (NDR) in organic nanocomposite unipolar resistive memory devices. From the analysis of the 1/f(γ) type noises, scaling behavior between the relative noise power spectral density S̃ and resistance R was observed, indicating a percolating behavior. Considering a linear rate equation of the charge trapping-detrapping at traps, the percolation behavior and NDR could be understood by the modulation of the conductive phase fraction φ with an external bias. This study can enhance the understanding of the NDR phenomena in organic nanocomposite unipolar resistive memory devices in terms of the current path formation and the memory switching.

  1. Early Maladaptive Schemas Related to Unipolar and Bipolar Depression: Similarities and Differences

    Directory of Open Access Journals (Sweden)

    Nergis LAPSEKÝLÝ

    2012-12-01

    Conclusion: In patient groups, schemas like defectiveness, incompetence, failure, vulnerability to danger and undeveloped self were indicative of low self-perception. This case draws attention to distortions in self-perception. When the absence of difference between bipolar and controls in “mistrust/abuse” and “abandonment/instability” schemas is evaluated in terms of cognitive triad, it is suggested that Environmental perspective in this group of patients did not exhibit pessimistic features. The only significantly different schema between unipolar and bipolar groups was “mistrust/abuse”. This suggests that bipolar group didn’t have negative thoughts like unipolar patients about the perception of the enviroment. [JCBPR 2012; 1(3.000: 145-151

  2. Daylight savings time transitions and the incidence rate of unipolar depressive episodes

    DEFF Research Database (Denmark)

    Hansen, Bertel T; Sønderskov, Kim M; Hageman, Ida

    2017-01-01

    Background: Daylight savings time transitions affect approximately 1.6 billion people worldwide. Prior studies have documented associations between daylight savings time transitions and adverse health outcomes, but it remains unknown whether they also cause an increase in the incidence rate...... of depressive episodes. This seems likely because daylight savings time transitions affect circadian rhythms, which are implicated in the etiology of depressive disorder. Therefore, we investigated the effects of daylight savings time transitions on the incidence rate of unipolar depressive episodes. Methods......: Using time series intervention analysis of nationwide data from the Danish Psychiatric Central Research Register from 1995 to 2012, we compared the observed trend in the incidence rate of hospital contacts for unipolar depressive episodes after the transitions to and from summer time to the predicted...

  3. Quantum anomalous Hall effect in magnetically modulated topological insulator/normal insulator heterostructures

    Science.gov (United States)

    Men'shov, V. N.; Tugushev, V. V.; Chulkov, E. V.

    2016-10-01

    We theoretically study how magnetic modulation can be used to manipulate the transport properties of heterostructures formed by a thin film of a three-dimensional topological insulator sandwiched between slabs of a normal insulator. Employing the k • p scheme, in the framework of a continual approach, we argue that electron states of the system are spin-polarized when ultrathin magnetic insertions are incorporated into the film. We demonstrate that (i) the spin-polarization magnitude depends strongly on the magnetic insertion position in the film and (ii) there is the optimal insertion position to realize quantum anomalous Hall effect, which is a function of the material parameters, the film thickness and the topological insulator/normal insulator interface potential. For the heterostructure with a pair of symmetrically placed magnetic insertions, we calculate a phase diagram that shows a series of transitions between distinct quantum regimes of transverse conductivity. We provide consistent interpretation of recent experimental findings in the context of our results.

  4. Semiclassical treatment of transport and spin relaxation in spin-orbit coupled systems

    Energy Technology Data Exchange (ETDEWEB)

    Lueffe, Matthias Clemens

    2012-02-10

    The coupling of orbital motion and spin, as derived from the relativistic Dirac equation, plays an important role not only in the atomic spectra but as well in solid state physics. Spin-orbit interactions are fundamental for the young research field of semiconductor spintronics, which is inspired by the idea to use the electron's spin instead of its charge for fast and power saving information processing in the future. However, on the route towards a functional spin transistor there is still some groundwork to be done, e.g., concerning the detailed understanding of spin relaxation in semiconductors. The first part of the present thesis can be placed in this context. We have investigated the processes contributing to the relaxation of a particularly long-lived spin-density wave, which can exist in semiconductor heterostructures with Dresselhaus and Rashba spin-orbit coupling of precisely the same magnitude. We have used a semiclassical spindiffusion equation to study the influence of the Coulomb interaction on the lifetime of this persistent spin helix. We have thus established that, in the presence of perturbations that violate the special symmetry of the problem, electron-electron scattering can have an impact on the relaxation of the spin helix. The resulting temperature-dependent lifetime reproduces the experimentally observed one in a satisfactory manner. It turns out that cubic Dresselhaus spin-orbit coupling is the most important symmetry-breaking element. The Coulomb interaction affects the dynamics of the persistent spin helix also via an Hartree-Fock exchange field. As a consequence, the individual spins precess about the vector of the surrounding local spin density, thus causing a nonlinear dynamics. We have shown that, for an experimentally accessible degree of initial spin polarization, characteristic non-linear effects such as a dramatic increase of lifetime and the appearance of higher harmonics can be expected. Another fascinating solid

  5. Platelet parameters (PLT, MPV, P-LCR) in patients with schizophrenia, unipolar depression and bipolar disorder.

    Science.gov (United States)

    Wysokiński, Adam; Szczepocka, Ewa

    2016-03-30

    There are no studies comparing platelet parameters platelet parameters (platelet count (PLT), mean platelet volume (MPV) and platelet large cell ratio (P-LCR)) between patients with schizophrenia, bipolar disorder and unipolar depression. Therefore, the aim of this study was to determine and compare differences in PLT, MPV and P-LCR in patients with schizophrenia, unipolar depression and bipolar disorder. This was a retrospective, cross-sectional, naturalistic study of 2377 patients (schizophrenia n=1243; unipolar depression n=791; bipolar disorder n=343, including bipolar depression n=259 and mania n=84). There were significant differences for PLT, MPV and P-LCR values between study groups. A significant percentage of patients with bipolar disorder had abnormal (too low or too high) number of platelets. Negative correlation between PLT and age was found in all study groups and positive correlation between age and MPV and P-LCR was found in patients with schizophrenia. Copyright © 2016 Elsevier Ireland Ltd. All rights reserved.

  6. Premorbid intelligence and educational level in bipolar and unipolar disorders: a Danish draft board study.

    Science.gov (United States)

    Sørensen, Holger Jelling; Sæbye, Ditte; Urfer-Parnas, Annick; Mortensen, Erik Lykke; Parnas, Josef

    2012-02-01

    Registry-based studies have found no or weak associations between premorbid intelligence and the broad entity of affective spectrum disorder, but none of the studies compared bipolar/unipolar subgroups. IQ and educational level were assessed at the draft board, and hospital diagnoses were followed up to the ages 43-54 years for 294 individuals hospitalized with bipolar disorder and 1434 with unipolar or depressive disorder. Controls comprised 20,531 individuals without psychiatric registration. Mean IQs of 98.32 and 96.71 were observed for patients with bipolar and depressive disorder respectively. For both patient groups a unimodal, slightly negatively skewed distribution was observed. The difference between the two patient samples was not statistically significant (p=0.10), but both obtained lower mean scores than the controls (pintelligence and educational level in patients with bipolar disorder compared with patients with unipolar disorder. However, we were unable to confirm distinct subgroups of bipolar disorder with high and low premorbid intelligence and educational level. Copyright © 2011 Elsevier B.V. All rights reserved.

  7. Mood Linked Responses in Medial Prefrontal Cortex Predict Relapse in Patients with Recurrent Unipolar Depression

    Science.gov (United States)

    Farb, Norman A. S.; Anderson, Adam K.; Bloch, Richard T.; Segal, Zindel V.

    2011-01-01

    Background Altered cognitive processing following mood challenge is associated with elevated relapse risk in remitted unipolar depressed patients, but little is known about the neural basis of this reactivity and its link to depressive relapse and prophylaxis. Methods Remitted unipolar depressed participants (n = 16) and healthy controls (n = 16) underwent functional magnetic resonance imaging (fMRI) while viewing sad and neutral film clips. Correlations were determined between emotional reactivity (neural responses to sad vs. neutral films) in remitted patients and subsequent relapse status over an 18 month follow-up period. An ROC analysis was used to determine signal cutoffs for predicting relapse. Emotional reactivity in relapse prognostic areas was compared between groups. Results Within the remitted group, relapse was predicted by medial prefrontal cortical activity (MPFC, BA 32), and contraindicated by visual cortical activity (BA 17). MPFC reactivity predicted rumination, whereas visual cortical reactivity predicted distress tolerance (acceptance). Compared to control participants, remitted depressed patients who sustained remission demonstrated a more pronounced tradeoff between MPFC and visual cortex reactivity. The difference score between MPFC and visual reactivity yielded excellent prediction of depressive relapse. Conclusions Medial prefrontal cortical reactivity to mood provocation in remitted unipolar depressed patients serves as a marker of relapse risk rather than successful emotion regulation. Enduring remission is characterized by a normalization of the MPFC to the level of healthy controls. Further, visual cortex reactivity predicts resilience against depressive relapse, indicating a prophylactic role for sensory rather than ruminative cognitive reactivity in the processing of negative emotion. PMID:21531382

  8. Exfoliation of the tungsten fibreform nanostructure by unipolar arcing in the LHD divertor plasma

    Science.gov (United States)

    Tokitani, M.; Kajita, S.; Masuzaki, S.; Hirahata, Y.; Ohno, N.; Tanabe, T.; LHD Experiment Group

    2011-10-01

    The tungsten nanostructure (W-fuzz) created in the linear divertor simulator (NAGDIS) was exposed to the Large Helical Device (LHD) divertor plasma for only 2 s (1 shot) to study exfoliation/erosion and microscopic modifications due to the high heat/particle loading under high magnetic field conditions. Very fine and randomly moved unipolar arc trails were clearly observed on about half of the W-fuzz area (6 × 10 mm2). The fuzzy surface was exfoliated by continuously moving arc spots even for the very short exposure time. This is the first observation of unipolar arcing and exfoliation of some areas of the W-fuzz structure itself in a large plasma confinement device with a high magnetic field. The typical width and depth of each arc trail were about 8 µm and 1 µm, respectively, and the arc spots moved randomly on the micrometre scale. The fractality of the arc trails was analysed using a box-counting method, and the fractal dimension (D) of the arc trails was estimated to be D ≈ 1.922. This value indicated that the arc spots moved in Brownian motion, and were scarcely influenced by the magnetic field. One should note that such a large scale exfoliation due to unipolar arcing may enhance the surface erosion of the tungsten armour and act as a serious impurity source for fusion plasmas.

  9. Latent Bipolarity In Unipolar Depression: Experimental Findings, Conceptual Analysis And Implications For Treatment Strategies.

    Science.gov (United States)

    Terziivanova, Petya D; Haralanov, Svetlozar H

    2014-01-01

    Previous studies have suggested that the two opposite poles of psychomotor disturbances in unipolar depression (UD) - retardation and agitation - require different treatment strategies as the psychomotor overactivation requires an augmentation of the antidepressant therapy with mood stabilizers and/or atypical antipsychotics. The aim of the present study was to objectively identify and measure the psycho-motor disturbances in UD using differentiation between activity and reactivity. An equilibriometric movement pattern analysis system that allows differentiation between psychomotor activity and reactivity was applied in 58 unipolar depressive patients and 76 healthy controls. Compared to controls, the patients as a group were significantly slower in their psychomotor reactivity. However, the subsequent subgrouping according to the direction of deviation of their objective psychomotor parameters revealed a disinhibition of psychomotor activity and/or reactivity in about one half of them. Such a contradictory combination of clinically manifested depressive mood and subclinically detected manic-like psychomotor overactivation might be regarded as belonging to the bipolar spectrum, since it was admitted that manic psychomotor disinhibition in unipolar depressive patients uncovers a latent bipolarity. Not only prototypical depressive inhibition, but also prototypical manic-like disinhibition may underlie clinically manifested UD. Since the combination between depressive mood and psychomotor overactivation multiplies the suicidal risk, we may presume that the timely detection of this combination at a subclinical level would contribute to an earlier and more effective suicidal prevention by an objectively-guided optimization of pharmacological treatment.

  10. Tunable electronic structure in stained two dimensional van der Waals g-C2N/XSe2 (X = Mo, W) heterostructures

    Science.gov (United States)

    Zheng, Z. D.; Wang, X. C.; Mi, W. B.

    2017-10-01

    The electronic structure of the strained g-C2N/XSe2 (X=Mo, W) van der Waals heterostructures are investigated by first-principles calculations. The g-C2N/MoSe2 heterostructure is an indirect band gap semiconductor at a strain from 0% to 8%, where its band gap is 0.66, 0.61, 0.73, 0.60 and 0.33 eV. At K point, the spin splitting is 186, 181, 39, 13 and 9 meV, respectively. For g-C2N/WSe2 heterostructures, the band gap is 0.32, 0.37, 0.42, 0.45 and 0.36 eV, and the conduction band minimum is shifted from Г-M region to K-Г region as the strain increases from 0% to 8%. Its spin splitting monotonically decreases as a strain raises to 8%, which is 445, 424, 261, 111 and 96 meV, respectively. Moreover, at a strain less than 4%, the conduction band mainly comes from g-C2N, but it comes from XSe2 (X=Mo, W) above 6%. Our results show that the g-C2N/XSe2 heterostructures have tunable electronic structures, which makes it a potential candidate for novel electronic devices.

  11. Spin ejector

    Science.gov (United States)

    Andersen, John A.; Flanigan, John J.; Kindley, Robert J.

    1978-01-01

    The disclosure relates to an apparatus for spin ejecting a body having a flat plate base containing bosses. The apparatus has a base plate and a main ejection shaft extending perpendicularly from the base plate. A compressible cylindrical spring is disposed about the shaft. Bearings are located between the shaft and the spring. A housing containing a helical aperture releasably engages the base plate and surrounds the shaft bearings and the spring. A piston having an aperture follower disposed in the housing aperture is seated on the spring and is guided by the shaft and the aperture. The spring is compressed and when released causes the piston to spin eject the body.

  12. Unipolar versus bipolar radiofrequency treatment of rhytides and laxity using a mobile painless delivery method.

    Science.gov (United States)

    Alexiades-Armenakas, Macrene; Dover, Jeffrey S; Arndt, Kenneth A

    2008-09-01

    Previous studies have shown that radiofrequency (RF) energy is a safe and effective treatment for rhytide-reduction. This randomized, blinded, split-face study assesses the safety and efficacy of the unipolar versus bipolar handpieces on an RF device with a mobile delivery method for the treatment of rhytides and laxity using quantitative grading. In this randomized, blinded, split-face design study, 10 subjects (aged 18-75 years) with a clinically observable excess of rhytides and laxity (minimum grade 2 out of 4) on the face received four treatments at 1-week intervals with random assignment of unipolar RF to one side and bipolar RF to the contralateral side. Each side received approximately four passes per treatment delivered in a mobile continuous manner. Results were evaluated by two blinded investigators of photographs employing a comprehensive 4-point grading scale at baseline, and 1- and 3-month follow-up visits after the final treatment. All subjects completed and responded to treatment. The blinded evaluations demonstrated the following mean percent improvements in grading scores of rhytides and laxity: for the unipolar side 6.0+/-4.6% and 4.6+/-4.8% versus the bipolar side 4.4+/-2.5 and 7.3+/-3.5%. The degree of improvement approached but did not achieve statistical significance for either handpiece, but demonstrated a trend toward improvement (P = 0.5599 unipolar vs. 0.1108 bipolar). The treatment was painless (rated 0 out of 10 by all subjects) and side effects included minimal erythema which resolved within 1-3 hours. No crusting, dyspigmentation or scarring was observed. This randomized, split-face study with blinded evaluations employing a quantitative grading scale demonstrated that minimal pass, mobile energy delivery serial treatments with either the unipolar or bipolar handpieces of a novel RF device appears to safe and painless. Each handpiece demonstrated minimal clinical efficacy which was not statistically significant, but with a trend

  13. Heterostructures based on inorganic and organic van der Waals systems

    Directory of Open Access Journals (Sweden)

    Gwan-Hyoung Lee

    2014-09-01

    Full Text Available The two-dimensional limit of layered materials has recently been realized through the use of van der Waals (vdW heterostructures composed of weakly interacting layers. In this paper, we describe two different classes of vdW heterostructures: inorganic vdW heterostructures prepared by co-lamination and restacking; and organic-inorganic hetero-epitaxy created by physical vapor deposition of organic molecule crystals on an inorganic vdW substrate. Both types of heterostructures exhibit atomically clean vdW interfaces. Employing such vdW heterostructures, we have demonstrated various novel devices, including graphene/hexagonal boron nitride (hBN and MoS2 heterostructures for memory devices; graphene/MoS2/WSe2/graphene vertical p-n junctions for photovoltaic devices, and organic crystals on hBN with graphene electrodes for high-performance transistors.

  14. Controlling electron quantum dot qubits by spin-orbit interactions

    Energy Technology Data Exchange (ETDEWEB)

    Stano, P.

    2007-01-15

    Single electron confined in a quantum dot is studied. A special emphasis is laid on the spin properties and the influence of spin-orbit interactions on the system. The study is motivated by a perspective exploitation of the spin of the confined electron as a qubit, a basic building block of in a foreseen quantum computer. The electron is described using the single band effective mass approximation, with parameters typical for a lateral electrostatically defined quantum dot in a GaAs/AlGaAs heterostructure. The stemming data for the analysis are obtained by numerical methods of exact diagonalization, however, all important conclusions are explained analytically. The work focuses on three main areas -- electron spectrum, phonon induced relaxation and electrically and magnetically induced Rabi oscillations. It is shown, how spin-orbit interactions influence the energy spectrum, cause finite spin relaxation and allow for all-electrical manipulation of the spin qubit. Among the main results is the discovery of easy passages, where the spin relaxation is unusually slow and the qubit is protected against parasitic electrical fields connected with manipulation by resonant electromagnetic fields. The results provide direct guide for manufacturing quantum dots with much improved properties, suitable for realizing single electron spin qubits. (orig.)

  15. Ab initio studies of coherent spin transport in Fe-hBN/graphene van der Waals multilayers.

    Science.gov (United States)

    Ukpong, Aniekan Magnus

    2017-07-19

    This paper presents the results of ab initio studies of the electronic spin inversion and filtering in a ferromagnetic multilayer heterostructure. Spin-polarized electronic structure calculations are performed based on van der Waals density functional theory to give unique insights in to the generation, manipulation and transport of coherent spin conductance. By using an exact theory of the self-consistent ground state of the Fe-hBN/graphene multilayer as a model of the magnetic tunnel junction, hidden asymmetries are unraveled in the spin-resolved charge densities. It is shown that the injection of spin into the graphene/boron nitride tunnel layer from a ferromagnetic contact gives rise to coherent spin current. The projected Fermi surfaces of the up and down spin channels are analyzed to reveal Fermi arc topologies and spin anisotropies. It is also demonstrated that the coherent transport of pure spin-down current in the topological Weyl semimetal phase is robust. The implications of the results on out-of-plane transport of spin polarized conductance in van der Waals multilayer spintronic devices is discussed. The insights derived from this study are expected to open up prospects for further exploration of van der Waals magnetic multilayer heterostructures as a versatile platform for developing materials for Weyltronic applications.

  16. Spinning worlds

    NARCIS (Netherlands)

    Schwarz, H.

    2017-01-01

    The thesis "Spinning Worlds" is about the characterisation of two types of gas-giant exoplanets: Hot Jupiters, with orbital periods of fewer than five days, and young, wide-orbit gas giants, with orbital periods as long as thousands of years. The thesis is based on near-infrared observations of 1

  17. Time-resolved studies of current-induced spin polarization in strained InGaAs/GaAs structures

    Energy Technology Data Exchange (ETDEWEB)

    Hagedorn, Markus [II. Phys. Institut A, RWTH Aachen University (Germany); Institut fuer Bio- und Nanosysteme (IBN-1), Forschungszentrum Juelich (Germany); JARA - Fundamentals of Future Information Technology (Germany); Kuhlen, Sebastian; Patt, Marten; Schlammes, Paul; Klein, Frederik; Goebbels, Stefan; Guentherodt, Gernot; Beschoten, Bernd [II. Phys. Institut A, RWTH Aachen University (Germany); JARA - Fundamentals of Future Information Technology (Germany); Lepsa, Mihail; Schaepers, Thomas [Institut fuer Bio- und Nanosysteme (IBN-1), Forschungszentrum Juelich (Germany); JARA - Fundamentals of Future Information Technology (Germany)

    2010-07-01

    Understanding the mechanisms of electron spin interactions and dephasing in nonmagnetic semiconductor heterostructures are crucial for building novel spintronic devices. Conventional all-optical pump/probe methods for the creation and detection of coherent spins are nowadays supplemented by means of electrical techniques. The underlying mechanisms which enable the so-called current induced spin polarization (CISP) are internal effective magnetic fields evoked by the broken inversion symmetry of the zinc blende structure in III-V semiconductor materials (Dresselhaus term) and, additionally, by strain in, e.g., InGaAs/GaAs heterostructures. Applying ultrafast current pulses (time-resolved CISP) to lateral transport devices without ferromagnetic contacts, we are able to create and manipulate phase coherent spin ensembles, which are probed by Faraday rotation.

  18. Analysis of Critical Dimensions for Nanowire Core-Multishell Heterostructures

    OpenAIRE

    Yan, Xin; Fan, Shuyu; Zhang, Xia; Ren, Xiaomin

    2015-01-01

    Critical dimensions for nanowire core-multishell heterostructures are analyzed by using finite-element method based on the energy equilibrium criteria. Results show that the nanowire core-shell heterostructure can sufficiently reduce the strain in the shell and increase the critical shell thickness. The critical dimensions for the nanowire core-multishell heterostructure are determined by the stress fields generated at two heterointerfaces. For thin barrier, the critical dimensions decrease a...

  19. A review of nano-optics in metamaterial hybrid heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Singh, Mahi R. [Department of Physics and Astronomy, Western University, London N6G 3K7 (Canada)

    2014-03-31

    We present a review for the nonlinear nano-optics in quantum dots doped in a metamaterial heterostructure. The heterostructure is formed by depositing a metamaterial on a dielectric substrate and ensemble of noninteracting quantum dots are doped near the heterostructure interface. It is shown that there is enhancement of the second harmonic generation due to the surface plasmon polaritons field present at the interface.

  20. Spin currents, spin torques, and the concept of spin superfluidity

    OpenAIRE

    Rückriegel, Andreas; Kopietz, Peter

    2017-01-01

    In magnets with non-collinear spin configuration the expectation value of the conventionally defined spin current operator contains a contribution which renormalizes an external magnetic field and hence affects only the precessional motion of the spin polarization. This term, which has been named angular spin current by Sun and Xie [Phys. Rev B 72, 245305 (2005)], does not describe the translational motion of magnetic moments. We give a prescription how to separate these two types of spin tra...

  1. Evidence for spin to charge conversion in GeTe(111

    Directory of Open Access Journals (Sweden)

    C. Rinaldi

    2016-03-01

    Full Text Available GeTe has been predicted to be the father compound of a new class of multifunctional materials, ferroelectric Rashba semiconductors, displaying a coupling between spin-dependent k-splitting and ferroelectricity. In this paper, we report on epitaxial Fe/GeTe(111 heterostructures grown by molecular beam epitaxy. Spin-pumping experiments have been performed in a radio-frequency cavity by pumping a spin current from the Fe layer into GeTe at the Fe ferromagnetic resonance and detecting the transverse charge current originated in the slab due to spin-to-charge conversion. Preliminary experiments indicate that a clear spin to charge conversion exists, thus unveiling the potential of GeTe for spin-orbitronics.

  2. Graphene-based half-metal and spin-semiconductor for spintronic applications

    Science.gov (United States)

    Qi, Jingshan; Chen, Xiaofang; Hu, Kaige; Feng, Ji

    2016-03-01

    In this letter we propose a strategy to make graphene become a half-metal or spin-semiconductor by combining the magnetic proximity effects and sublattice symmetry breaking in graphone/graphene and graphone/graphene/BN heterostructures. Exchange interactions lift the spin degeneracy and sublattice symmetry breaking opens a band gap in graphene. More interestingly, the gap opening depends on the spin direction and the competition between the sublattice asymmetry and exchange field determines the system is a half-metal or a spin-semiconductor. By first-principles calculations and a low-energy effective model analysis, we elucidate the underlying physical mechanism of spin-dependent gap opening and spin degeneracy splitting. This offers an alternative practical platform for graphene-based spintronics.

  3. Coupled magnetic and elastic dynamics generated by a shear wave propagating in ferromagnetic heterostructure

    Science.gov (United States)

    Azovtsev, A. V.; Pertsev, N. A.

    2017-11-01

    Using advanced micromagnetic simulations, we describe the coupled elastic and magnetic dynamics induced in ferromagnet/normal metal bilayers by shear waves generated by the attached piezoelectric transducer. Our approach is based on the numerical solution of a system of differential equations, which comprises the Landau-Lifshitz-Gilbert equation and the elastodynamic equation of motion, both allowing for the magnetoelastic coupling between spins and lattice strains. The simulations have been performed for heterostructures involving a Fe81Ga19 layer with the thickness ranging from 100 to 892 nm and a few-micrometer-thick film of a normal metal (Au). We find that the traveling shear wave induces inhomogeneous magnetic dynamics in the ferromagnetic layer, which generally has an intermediate character between coherent magnetization precession and the pure spin wave. Owing to the magnetoelastic feedback, the magnetization precession generates two additional elastic waves (shear and longitudinal), which propagate into the normal metal. Despite such complex elastic dynamics and reflections of elastic waves at the Fe81Ga19|Au interface, periodic magnetization precession with the excitation frequency settles in the steady-state regime. The results obtained for the magnetization dynamics at the Fe81Ga19|Au interface are used to evaluate the spin current pumped into the Au layer and the accompanying charge current caused by the inverse spin Hall effect. The calculations show that the dc component of the charge current is high enough to be detected experimentally even at small strains ˜10-4 generated by the piezoelectric transducer.

  4. Two-dimensional hole systems in indium-based quantum well heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Loher, Josef

    2016-08-01

    The complex spin-orbit interaction (SOI) of two-dimensional hole gas (2DHG) systems - the relativistic coupling of the hole spin degree of freedom to their movement in an electric field - is of fundamental interest in spin physics due to its key role for spin manipulation in spintronic devices. In this work, we were able to evaluate the tunability of Rashba-SOI-related parameters in the 2DHG system of InAlAs/InGaAs/InAs:Mn quantum well heterostructures experimentally by analyzing the hole density evolution of quantum interference effects at low magnetic fields. We achieved to cover a significant range of hole densities by the joint action of the variation of the manganese modulation doping concentration during molecular beam epitaxy and external field-effect-mediated manipulation of the 2D carrier density in Hall bar devices by a metallic topgate. Within these magnetotransport experiments, a reproducible phenomenon of remarkable robustness emerged in the transverse Hall magnetoresistivity of the indium 2DHG systems which are grown on a special InAlAs step-graded metamorphic buffer layer structure to compensate crystal lattice mismatch. As a consequence of the strain relaxation process, these material systems are characterized by anisotropic properties along different crystallographic directions. We identify a puzzling offset phenomenon in the zero-field Hall magnetoresistance and demonstrate it to be a universal effect in systems with spatially anisotropic transport properties.

  5. Thermal response in van der Waals heterostructures

    KAUST Repository

    Gandi, Appala

    2016-11-21

    We solve numerically the Boltzmann transport equations of the phonons and electrons to understand the thermoelectric response in heterostructures of M2CO2 (M: Ti, Zr, Hf) MXenes with transition metal dichalcogenide monolayers. Low frequency optical phonons are found to occur as a consequence of the van der Waals bonding, contribute significantly to the thermal transport, and compensate for the reduced contributions of the acoustic phonons (increased scattering cross-sections in heterostructures), such that the thermal conductivities turn out to be similar to those of the bare MXenes. Our results indicate that the important superlattice design approach of thermoelectrics (to reduce the thermal conductivity) may be effective for two-dimensional van der Waals materials when used in conjunction with intercalation. © 2016 IOP Publishing Ltd.

  6. Phonon engineering in proximity enhanced superconductor heterostructures.

    Science.gov (United States)

    Tang, Yong-Chao; Kwon, Sangil; Mohebbi, Hamid R; Cory, David G; Miao, Guo-Xing

    2017-06-27

    In this research, we tailor the phonon density of states (DOS) in thin superconducting films to suppress quasiparticle losses. We examine a model system of a proximity-enhanced three-layered Al/Nb/Al heterostructure and show that the local quantized phonon spectrum of the ultrathin Al cladding layers in the heterostructure has a pronounced effect on the superconducting resonator's quality factors. Instead of a monotonic increase of quality factors with decreasing temperatures, we observe the quality factor reaches a maximum at 1.2 K in 5/50/5 nm Al/Nb/Al microstrip resonators, because of a quantized phonon ladder. The phonon DOS may be engineered to enhance the performance of quantum devices.

  7. Lateral shifts of spin electron beams in antiparallel double {delta}-magnetic-barrier nanostructure

    Energy Technology Data Exchange (ETDEWEB)

    Kong Yonghong [Department of Electronic Engineering, Hunan University Science and Engineering, Hunan 425100 (China); Lu Maowang, E-mail: m_w_lu@126.com [Department of Electronic Engineering, Hunan University Science and Engineering, Hunan 425100 (China); Chen Saiyan; Zhang Guilian [Department of Electronic Engineering, Hunan University Science and Engineering, Hunan 425100 (China)

    2012-08-15

    We investigate the Goos-Haenchen (GH) effect of spin electron beams in a magnetic-barrier (MB) nanostructure consisting of antiparallel double {delta}-MBs, which can be experimentally realized by depositing two ferromagnetic (FM) stripes on top and bottom of the semiconductor heterostructure. GH shifts for spin electron beams across this type of MB nanostructures, is derived exactly, with the help of the stationary phase method. It is shown that GH shifts depend strongly on the spin directions for double {delta}-MBs with unidentical magnetic strengths, giving rise to a considerable spin polarization effect. It also is shown that spin polarization of GH shifts is closely relative to the separation and magnetic-strength difference of two {delta}-MBs. These interesting properties may provide an alternative scheme to spin-polarize electrons into the semiconductor, and the devices can serve as tunable spin beam splitters. - Highlights: Black-Right-Pointing-Pointer Spin Goos-Haenchen effect of electron beams through a kind of MB nanostructures. Black-Right-Pointing-Pointer GH shift depends greatly on electron-spins, which is used to spin polarize electrons in semiconductor. Black-Right-Pointing-Pointer Spin polarization in GH shift is tunable. Black-Right-Pointing-Pointer A tunable spin beam splitter is achieved.

  8. Proximity coupling in superconductor-graphene heterostructures

    OpenAIRE

    Lee, Gil-Ho; Lee, Hu-Jong

    2017-01-01

    This review discusses the electronic properties and the prospective research directions of superconductor-graphene heterostructures. The basic electronic properties of graphene are introduced to highlight the unique possibility of combining two seemingly unrelated physics, superconductivity and relativity. We then focus on graphene-based Josephson junctions, one of the most versatile superconducting quantum devices. The various theoretical methods that have been developed to describe graphene...

  9. Voltage control of magnetism in multiferroic heterostructures.

    Science.gov (United States)

    Liu, Ming; Sun, Nian X

    2014-02-28

    Electrical tuning of magnetism is of great fundamental and technical importance for fast, compact and ultra-low power electronic devices. Multiferroics, simultaneously exhibiting ferroelectricity and ferromagnetism, have attracted much interest owing to the capability of controlling magnetism by an electric field through magnetoelectric (ME) coupling. In particular, strong strain-mediated ME interaction observed in layered multiferroic heterostructures makes it practically possible for realizing electrically reconfigurable microwave devices, ultra-low power electronics and magnetoelectric random access memories (MERAMs). In this review, we demonstrate this remarkable E-field manipulation of magnetism in various multiferroic composite systems, aiming at the creation of novel compact, lightweight, energy-efficient and tunable electronic and microwave devices. First of all, tunable microwave devices are demonstrated based on ferrite/ferroelectric and magnetic-metal/ferroelectric composites, showing giant ferromagnetic resonance (FMR) tunability with narrow FMR linewidth. Then, E-field manipulation of magnetoresistance in multiferroic anisotropic magnetoresistance and giant magnetoresistance devices for achieving low-power electronic devices is discussed. Finally, E-field control of exchange-bias and deterministic magnetization switching is demonstrated in exchange-coupled antiferromagnetic/ferromagnetic/ferroelectric multiferroic hetero-structures at room temperature, indicating an important step towards MERAMs. In addition, recent progress in electrically non-volatile tuning of magnetic states is also presented. These tunable multiferroic heterostructures and devices provide great opportunities for next-generation reconfigurable radio frequency/microwave communication systems and radars, spintronics, sensors and memories.

  10. Strain engineering of van der Waals heterostructures.

    Science.gov (United States)

    Vermeulen, Paul A; Mulder, Jefta; Momand, Jamo; Kooi, Bart J

    2018-01-18

    Modifying the strain state of solids allows control over a plethora of functional properties. The weak interlayer bonding in van der Waals (vdWaals) materials such as graphene, hBN, MoS2, and Bi2Te3 might seem to exclude strain engineering, since strain would immediately relax at the vdWaals interfaces. Here we present direct observations of the contrary by showing growth of vdWaals heterostructures with persistent in-plane strains up to 5% and we show that strain relaxation follows a not yet reported process distinctly different from strain relaxation in three-dimensionally bonded (3D) materials. For this, 2D bonded Bi2Te3-Sb2Te3 and 2D/3D bonded Bi2Te3-GeTe multilayered films are grown using Pulsed Laser Deposition (PLD) and their structure is monitored in situ using Reflective High Energy Electron Diffraction (RHEED) and post situ analysis is performed using Transmission Electron Microscopy (TEM). Strain relaxation is modeled and found to solely depend on the layer being grown and its initial strain. This insight demonstrates that strain engineering of 2D bonded heterostructures obeys different rules than hold for epitaxial 3D materials and opens the door to precise tuning of the strain state of the individual layers to optimize functional performance of vdWaals heterostructures.

  11. spin coating

    African Journals Online (AJOL)

    PROJET SOJA

    Intense UV photoluminescence is observed for intrinsic ZnO film. Keywords : thin films, oxidize zinc doped aluminium (ZnO:Al), sol-gel, spin coating, structural analysis, electric and optical properties. 1. Introduction. Depuis ces vingt dernières années les couches minces d'oxyde de zinc ont connu un intérêt croissant dans ...

  12. Spin-Circuit Representation of Spin Pumping

    Science.gov (United States)

    Roy, Kuntal

    2017-07-01

    Circuit theory has been tremendously successful in translating physical equations into circuit elements in an organized form for further analysis and proposing creative designs for applications. With the advent of new materials and phenomena in the field of spintronics and nanomagnetics, it is imperative to construct the spin-circuit representations for different materials and phenomena. Spin pumping is a phenomenon by which a pure spin current can be injected into the adjacent layers. If the adjacent layer is a material with a high spin-orbit coupling, a considerable amount of charge voltage can be generated via the inverse spin Hall effect allowing spin detection. Here we develop the spin-circuit representation of spin pumping. We then combine it with the spin-circuit representation for the materials having spin Hall effect to show that it reproduces the standard results as in the literature. We further show how complex multilayers can be analyzed by simply writing a netlist.

  13. Superior anti-suicidal effects of electroconvulsive therapy in unipolar disorder and bipolar depression.

    Science.gov (United States)

    Liang, Chih-Sung; Chung, Chi-Hsiang; Ho, Pei-Shen; Tsai, Chia-Kuang; Chien, Wu-Chien

    2017-12-11

    Electroconvulsive therapy (ECT) has long been believed to reduce suicidal tendencies in patients with affective disorders; however, ECT recipients, who constitute the most severely ill and suicidal patients, are not eligible to participate in head-to-head randomized controlled trials. Large-scale studies are required to investigate the anti-suicidal effects of ECT vs psychopharmacotherapy. A nationwide retrospective cohort study design was used. Data were obtained from the Taiwan National Health Insurance Research Database. Inpatients with unipolar disorder or bipolar disorder who received ECT (n = 487) were observed from 1 January 2000 to 31 December 2013 for suicide events. The non-ECT control cohort consisted of inpatients with psychopharmacotherapy randomly matched (ratio, 1:4) by age, sex, and diagnosis. After potential confounds had been accounted for, the adjusted hazard ratio (HR) was 0.803, indicating that ECT recipients showed a 19.7% lower risk of suicide than control individuals. The stratum-specific adjusted HR was 0.79 in patients with unipolar disorder (P = .041) and 0.923 in patients with bipolar disorder (P = .254). Upon further stratification of the patients with bipolar disorder by their affective states, the adjusted HR was 0.805 (P = .046) for bipolar depression, 1.048 for bipolar mania (P = .538), and 0.976 for mixed bipolar state (P = .126). Compared with psychopharmacotherapy, ECT exerted superior anti-suicidal effects in patients with unipolar disorder and bipolar depression; however, there was a lack of superior anti-suicidal effects of ECT in the treatment of patients with bipolar mania and mixed state. © 2017 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

  14. The unipolar ASR : Viable option in unsalvageable femoral head conditions in the young patient

    Directory of Open Access Journals (Sweden)

    Marya SKS

    2006-01-01

    Full Text Available Background: The management of unsalvageable femoral head conditions in the young patient has remained an unresolved dilemma. Articular surface replacement of the hip has recently made some headway in terms of providing near-normal hip joint mechanics and function. However, this surgery has been limited to early stages of arthritis only with reasonable maintenance of head-neck congruity and morphology. Femoral neck fractures, osteonecrosis with large segment collapse, advanced arthritis with femoral incongruity, etc are traditional contraindications to the resurfacing technique. Methods: We present here a report on our series of 20 cases of unsalvageable femoral heads in young patients (age range, 27 to 52yrs, over a twelve month period (Aug 2004 to Jul 2005, treated with the unipolar ASR prosthesis. Fifteen patients (two had bilateral hip pathology had primary or secondary arthritis (degenerative, post-traumatic, ankylosing spondylitis and post-avascular necrosis while three had old operated femoral neck fractures. All patients underwent hip replacement surgery using the Unipolar ASR prosthesis. Results: Clinical and radiological results at 6-month follow up have been very encouraging and warrant further study. At an average of 4 months post-operatively, patients were able to squat, sit on the ground and perform light sporting activities. Conclusions: The Unipolar ASR prosthesis is an extension of the articular resurfacing technique employing similar principles (large size bearings, metal-on-metal interfaces, and has incorporated the advantages of the uncemented technique. We propose that this technique be more frequently used so as to brighten the prognosis of the young active patient with unsalvageable hip conditions, especially in the Asian scenario.

  15. Unipolar and Bipolar High-Magnetic-Field Sensors Based on Surface Acoustic Wave Resonators

    Science.gov (United States)

    Polewczyk, V.; Dumesnil, K.; Lacour, D.; Moutaouekkil, M.; Mjahed, H.; Tiercelin, N.; Petit Watelot, S.; Mishra, H.; Dusch, Y.; Hage-Ali, S.; Elmazria, O.; Montaigne, F.; Talbi, A.; Bou Matar, O.; Hehn, M.

    2017-08-01

    While surface acoustic wave (SAW) sensors have been used to measure temperature, pressure, strains, and low magnetic fields, the capability to measure bipolar fields and high fields is lacking. In this paper, we report magnetic surface acoustic wave sensors that consist of interdigital transducers made of a single magnetostrictive material, either Ni or TbFe2 , or based on exchange-biased (Co /IrMn ) multilayers. By controlling the ferromagnet magnetic properties, high-field sensors can be obtained with unipolar or bipolar responses. The issue of hysteretic response of the ferromagnetic material is especially addressed, and the control of the magnetic properties ensures the reversible behavior in the SAW response.

  16. Failure of communication and capture: The perils of temporary unipolar pacing system

    Directory of Open Access Journals (Sweden)

    Efe Sahinoglu, BChE

    2015-06-01

    Full Text Available We present a case of a patient with pacemaker dependence secondary to complete heart block who developed loss of capture of her temporary pacemaker. Patient developed torsades de pointes then ventricular fibrillation, requiring CPR and external cardioversion. After patient was stabilized, it was noticed that loss of capture of pacemaker corresponded with nursing care, when the pulse generator was lifted off patient׳s chest wall, and that patient׳s temporary pacing system had been programmed to unipolar mode without knowledge of attending cardiologist. This case highlights the importance of communication ensuring all caregivers are aware of mode of the temporary pacing system.

  17. Are repeated assisted reproductive technology treatments and an unsuccessful outcome risk factors for unipolar depression in infertile women?

    DEFF Research Database (Denmark)

    Sejbaek, Camilla S; Pinborg, Anja; Hageman, Ida

    2015-01-01

    INTRODUCTION: Previous studies have shown conflicting results whether unsuccessful medically assisted reproduction is a risk factor for depression among women. This study therefore investigated if women with no live birth after assisted reproductive technology (ART) treatment had a higher risk...... of unipolar depression compared with women with a live birth after ART treatment. MATERIAL AND METHODS: The Danish National ART-Couple (DANAC) Cohort is a national register-based cohort study that consists of women who received ART treatment from 1 January 1994 to 30 September 2009, in Denmark (n = 41 050......). Information on unipolar depression was obtained from the Danish Psychiatric Central Research Register. The analyses were conducted in Cox regression analysis. RESULTS: During the 308 494 person-years of follow up, 552 women were diagnosed with unipolar depression. A Cox proportional hazards model showed...

  18. Manipulating Topological States by Imprinting Non-Collinear Spin Textures

    Science.gov (United States)

    Streubel, Robert; Han, Luyang; Im, Mi-Young; Kronast, Florian; Rößler, Ulrich K.; Radu, Florin; Abrudan, Radu; Lin, Gungun; Schmidt, Oliver G.; Fischer, Peter; Makarov, Denys

    2015-01-01

    Topological magnetic states, such as chiral skyrmions, are of great scientific interest and show huge potential for novel spintronics applications, provided their topological charges can be fully controlled. So far skyrmionic textures have been observed in noncentrosymmetric crystalline materials with low symmetry and at low temperatures. We propose theoretically and demonstrate experimentally the design of spin textures with topological charge densities that can be tailored at ambient temperatures. Tuning the interlayer coupling in vertically stacked nanopatterned magnetic heterostructures, such as a model system of a Co/Pd multilayer coupled to Permalloy, the in-plane non-collinear spin texture of one layer can be imprinted into the out-of-plane magnetised material. We observe distinct spin textures, e.g. vortices, magnetic swirls with tunable opening angle, donut states and skyrmion core configurations. We show that applying a small magnetic field, a reliable switching between topologically distinct textures can be achieved at remanence. PMID:25739643

  19. Manipulating Topological States by Imprinting Non Collinear Spin Textures

    Science.gov (United States)

    Fischer, Peter; Streubel, Robert; Han, Luyang; Im, Mi-Young; Kronast, Florian; Roessler, Ulrich K.; Radu, Florin; Abrudan, Radu; Lin, Gungun; Schmidt, Oliver G.; Makarov, Denys

    2015-03-01

    Topological magnetic states, such as chiral skyrmions, are of great scientific interest and show huge potential for novel spintronics applications, provided their topological charges can be fully controlled. So far skyrmionic textures have been observed in noncentrosymmetric crystalline materials with low symmetry and at low temperatures. We propose theoretically and demonstrate experimentally the design of spin textures with topological charge densities that can be tailored at ambient temperatures. Tuning the interlayer coupling in vertically stacked nanopatterned magnetic heterostructures, such as a model system of a Co/Pd multilayer coupled to Permalloy, the in-plane non-collinear spin texture of one layer can be imprinted into the out-of-plane magnetised material. We observe distinct spin textures, e.g. vortices, magnetic swirls with tunable opening angle, donut states and skyrmion systems of Dn symmetry. We show that applying a small magnetic field, a reliable switching between topologically distinct textures can be achieved at remanence.

  20. Manipulating Topological States by Imprinting Non-Collinear Spin Textures

    Science.gov (United States)

    Streubel, Robert; Han, Luyang; Im, Mi-Young; Kronast, Florian; Rößler, Ulrich K.; Radu, Florin; Abrudan, Radu; Lin, Gungun; Schmidt, Oliver G.; Fischer, Peter; Makarov, Denys

    2015-03-01

    Topological magnetic states, such as chiral skyrmions, are of great scientific interest and show huge potential for novel spintronics applications, provided their topological charges can be fully controlled. So far skyrmionic textures have been observed in noncentrosymmetric crystalline materials with low symmetry and at low temperatures. We propose theoretically and demonstrate experimentally the design of spin textures with topological charge densities that can be tailored at ambient temperatures. Tuning the interlayer coupling in vertically stacked nanopatterned magnetic heterostructures, such as a model system of a Co/Pd multilayer coupled to Permalloy, the in-plane non-collinear spin texture of one layer can be imprinted into the out-of-plane magnetised material. We observe distinct spin textures, e.g. vortices, magnetic swirls with tunable opening angle, donut states and skyrmion core configurations. We show that applying a small magnetic field, a reliable switching between topologically distinct textures can be achieved at remanence.

  1. General Considerations of the Electrostatic Boundary Conditions in Oxide Heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Higuchi, Takuya

    2011-08-19

    When the size of materials is comparable to the characteristic length scale of their physical properties, novel functionalities can emerge. For semiconductors, this is exemplified by the 'superlattice' concept of Esaki and Tsu, where the width of the repeated stacking of different semiconductors is comparable to the 'size' of the electrons, resulting in novel confined states now routinely used in opto-electronics. For metals, a good example is magnetic/non-magnetic multilayer films that are thinner than the spin-scattering length, from which giant magnetoresistance (GMR) emerged, used in the read heads of hard disk drives. For transition metal oxides, a similar research program is currently underway, broadly motivated by the vast array of physical properties that they host. This long-standing notion has been recently invigorated by the development of atomic-scale growth and probe techniques, which enables the study of complex oxide heterostructures approaching the precision idealized in Fig. 1(a). Taking the subset of oxides derived from the perovskite crystal structure, the close lattice match across many transition metal oxides presents the opportunity, in principle, to develop a 'universal' heteroepitaxial materials system. Hand-in-hand with the continual improvements in materials control, an increasingly relevant challenge is to understand the consequences of the electrostatic boundary conditions which arise in these structures. The essence of this issue can be seen in Fig. 1(b), where the charge sequence of the sublayer 'stacks' for various representative perovskites is shown in the ionic limit, in the (001) direction. To truly 'universally' incorporate different properties using different materials components, be it magnetism, ferroelectricity, superconductivity, etc., it is necessary to access and join different charge sequences, labelled here in analogy to the designations 'group IV, III-V, II

  2. Spin currents, spin torques, and the concept of spin superfluidity

    Science.gov (United States)

    Rückriegel, Andreas; Kopietz, Peter

    2017-03-01

    In magnets with noncollinear spin configuration the expectation value of the conventionally defined spin current operator contains a contribution which renormalizes an external magnetic field and hence affects only the precessional motion of the spin polarization. This term, which has been named angular spin current by Sun and Xie [Phys. Rev. B 72, 245305 (2005)], 10.1103/PhysRevB.72.245305, does not describe the translational motion of magnetic moments. We give a prescription for how to separate these two types of spin transport and show that the translational movement of the spin is always polarized along the direction of the local magnetization. We also show that at vanishing temperature the classical magnetic order parameter in magnetic insulators cannot carry a translational spin current and elucidate how this affects the interpretation of spin supercurrents.

  3. Discriminating unipolar and bipolar depression by means of fMRI and pattern classification: a pilot study.

    Science.gov (United States)

    Grotegerd, Dominik; Suslow, Thomas; Bauer, Jochen; Ohrmann, Patricia; Arolt, Volker; Stuhrmann, Anja; Heindel, Walter; Kugel, Harald; Dannlowski, Udo

    2013-03-01

    Bipolar disorders rank among the most debilitating psychiatric diseases. Bipolar depression is often misdiagnosed as unipolar depression, leading to suboptimal therapy and poor outcomes. Discriminating unipolar and bipolar depression at earlier stages of illness could therefore help to facilitate efficient and specific treatment. In the present study, the neurobiological underpinnings of emotion processing were investigated in a sample of unipolar and bipolar depressed patients matched for age, gender, and depression severity by means of fMRI. A pattern-classification approach was employed to discriminate the two samples. The pattern classification yielded up to 90 % accuracy rates discriminating the two groups. According to the feature weights of the multivariate maps, medial prefrontal and orbitofrontal regions contributed to classifications specific to unipolar depression, whereas stronger feature weights in dorsolateral prefrontal areas contribute to classifications as bipolar. Strong feature weights were observed in the amygdala for the negative faces condition, which were specific to unipolar depression, whereas higher amygdala features weights during the positive faces condition were observed, specific to bipolar subjects. Standard univariate fMRI analysis supports an interpretation, where this might be related to a higher responsiveness, by yielding a significant emotion × group interaction within the bilateral amygdala. We conclude that pattern-classification techniques could be a promising tool to classify acutely depressed subjects as unipolar or bipolar. However, since the present approach deals with small sample sizes, it should be considered as a proof-of-concept study. Hence, results have to be confirmed in larger samples preferably of unmedicated subjects.

  4. Relacionamentos multilaterais na unipolaridade: uma discussão teórica realista Multilateral relationships in unipolarity: a realist approach

    Directory of Open Access Journals (Sweden)

    Eugenio Diniz

    2006-12-01

    Full Text Available Examina-se em que medida e em que condições relacionamentos multilaterais podem ser relevantes no contexto de um sistema unipolar e, em particular, em que medida e em que condições esses relacionamentos podem influenciar o comportamento do único pólo do sistema. O artigo começa distinguindo um sistema internacional unipolar de um sistema estritamente hegemônico. A partir daí, identifica como variável-chave do sistema o comportamento de uma Potência Unipolar, e estabelece as bases teóricas desse comportamento, ou seja, sua Grande Estratégia ideal - abstrata, não descritiva -, como parâmetro de avaliação. Em seguida, estabelece as bases teóricas das possibilidades de sustentação dessa Grande Estratégia ideal, ou seja, a Política de Sustentação Grande-Estratégica ideal da Potência Unipolar. Das necessidades intrínsecas de cada uma, decorrem: (a a análise teórica da utilidade de relacionamentos multilaterais do ponto de vista da Potência Unipolar; (b a análise teórica do poder de barganha dos demais atores internacionais em face da Potência Unipolar no âmbito desses relacionamentos; (c a análise teórica da utilidade de aliados críticos, concretos e potenciais para a Potência Unipolar; e (d a análise teórica do poder de barganha de aliados críticos, concretos e potenciais, em face da Potência Unipolar. Com base nessas quatro análises, estabelecem-se as condições teóricas das variações na relevância desses relacionamentos multilaterais no sistema unipolar, bem como seus limites teóricos. A análise mostrará que, a partir das próprias premissas de alguns autores realistas, e respeitados aqueles limites, relacionamentos multilaterais têm o potencial de serem mais relevantes do que esses autores geralmente consideram, mas não são indispensáveis; desrespeitados aqueles limites, podem se tornar irrelevantes.The article focus on how relevant, and under what conditions, multilateral relationships are in

  5. spin coating

    African Journals Online (AJOL)

    PROJET SOJA

    Dans ce travail nous avons préparé des couches minces de l'oxyde de zinc ZnO dopées à l'aluminium et non dopées par la technique Sol-Gel associée au « spin coating » sur des substrats en verre « pyrex » à partir de l'acétate de zinc dissous dans une solution de l'éthanol. Nous avons ensuite effectué des analyses ...

  6. Straintronics in two-dimensional in-plane heterostructures of transition-metal dichalcogenides.

    Science.gov (United States)

    Wei, Wei; Dai, Ying; Huang, Baibiao

    2016-12-21

    For in-plane heterostructures between 2D transition-metal dichalcogenides (TMDs), namely, MoSe2/MoS2, MoS2/MoSe2, WSe2/MoS2 and MoS2/WSe2, intrinsic strain can be introduced resulting from lattice mismatch between two constituents, which significantly influences electronic properties (straintronics). Intrinsic strain can reduce or decrease the coupling strength between nonmetal p and metal d orbitals, and therefore modifies the splitting between bonding and antibonding states at the high-symmetry k-points. In this case, relative upward or downward shift of band edge at specific k-points leads to band gap reduction or enhancement and the indirect-direct band gap transition. Upon consideration of spin-orbit coupling (SOC) effects, energy splitting in valence bands will further shift the band edge at a specific k-point, and changes the band gap nature, such as indirect-direct band gap transition. It is of interest that intense states hybridization exists within the interline region, and therefore band alignments for in-plane heterostructures of 2D TMDs should be reconsidered, which is crucial for transport and optical features. In addition, states hybridization plays a role in the amplitude of band edge shift since individual 2D TMDs present different resistance to the strain. However, we found that intrinsic strain has no effects on the SOC-induced energy splitting in valence bands of these in-plane heterostructures, while the extent of states hybridization determines the magnitude of energy splitting. In addition, charge transfer across the interline also has effects on the band gap. In the presence of strain, the bonding strength of two 2D TMDs is reduced.

  7. Superconductivity-induced magnetization depletion in a ferromagnet through an insulator in a ferromagnet-insulator-superconductor hybrid oxide heterostructure.

    Science.gov (United States)

    Prajapat, C L; Singh, Surendra; Paul, Amitesh; Bhattacharya, D; Singh, M R; Mattauch, S; Ravikumar, G; Basu, S

    2016-05-21

    Coupling between superconducting and ferromagnetic states in hybrid oxide heterostructures is presently a topic of intense research. Such a coupling is due to the leakage of the Cooper pairs into the ferromagnet. However, tunneling of the Cooper pairs though an insulator was never considered plausible. Using depth sensitive polarized neutron reflectivity we demonstrate the coupling between superconductor and magnetic layers in epitaxial La2/3Ca1/3MnO3 (LCMO)/SrTiO3/YBa2Cu3O7-δ (YBCO) hybrid heterostructures, with SrTiO3 as an intervening oxide insulator layer between the ferromagnet and the superconductor. Measurements above and below the superconducting transition temperature (TSC) of YBCO demonstrate a large modulation of magnetization in the ferromagnetic layer below the TSC of YBCO in these heterostructures. This work highlights a unique tunneling phenomenon between the epitaxial layers of an oxide superconductor (YBCO) and a magnetic layer (LCMO) through an insulating layer. Our work would inspire further investigations on the fundamental aspect of a long range order of the triplet spin-pairing in hybrid structures.

  8. Exotic topological insulator states and topological phase transitions in Sb2Se3-Bi2Se3 heterostructures

    KAUST Repository

    Zhang, Qianfan

    2012-03-27

    Topological insulator is a new state of matter attracting tremendous interest due to its gapless linear dispersion and spin momentum locking topological states located near the surface. Heterostructures, which have traditionally been powerful in controlling the electronic properties of semiconductor devices, are interesting for topological insulators. Here, we studied the spatial distribution of the topological state in Sb 2Se 3-Bi 2Se 3 heterostructures by first-principle simulation and discovered that an exotic topological state exists. Surprisingly, the state migrates from the nontrivial Bi 2Se 3 into the trivial Sb 2Se 3 region and spreads across the entire Sb 2Se 3 slab, extending beyond the concept of "surface" state while preserving all of the topological surface state characteristics. This unusual topological state arises from the coupling between different materials and the modification of electronic structure near Fermi energy. Our study demonstrates that heterostructures can open up opportunities for controlling the real-space distribution of the topological state and inducing quantum phase transitions between topologically trivial and nontrivial states. © 2012 American Chemical Society.

  9. Spin-transport-phenomena in metals, semiconductors, and insulators

    Energy Technology Data Exchange (ETDEWEB)

    Althammer, Matthias Klaus

    2012-07-19

    /platinum heterostructures using two independent experiments based on the spin pumping effect. The yttrium iron garnet thin films were again deposited via laser-MBE and are state-of-the-art. Our results establish ferromagnetic insulator/normal metal structures as efficient spin current sources. Finally, we show that a new magnetoresistance effect due to spin currents is present in these ferromagnetic insulator/normal metal hybrids. This magnetoresistance effect in particular provides a simple means to establish spin current ow across the interface.

  10. Postpartum depression: bipolar or unipolar? Analysis of 434 Polish postpartum women.

    Science.gov (United States)

    Jaeschke, Rafał R; Dudek, Dominika; Topór-Mądry, Roman; Drozdowicz, Katarzyna; Datka, Wojciech; Siwek, Marcin; Rybakowski, Janusz

    2017-01-01

    To assess the prevalence of soft bipolar features in a sample of women with postpartum depressive symptoms, as well as to compare the sociodemographic and obstetric characteristics of subjects with bipolar or unipolar postpartum depressive symptomatology. Four hundred and thirty-four participants were enrolled in this cross-sectional study. Postpartum depression (PPD) symptoms were assessed using the Edinburgh Postnatal Depression Scale (EPDS), while the Mood Disorder Questionnaire (MDQ) was used to screen for bipolarity features. Of the 434 participants, 66 (15.2%) scored ≥ 13 points on the EPDS, thus fulfilling the screening criteria, and 103 scored ≥ 7 points on the MDQ. In comparison with non-depressed subjects, the women who scored positively on the EPDS were significantly more likely to exhibit symptoms of bipolar spectrum disorders (38 vs. 21%; chi-square test, p = 0.015). Women with bipolar PPD symptomatology were significantly younger than those exhibiting unipolar PPD symptoms (31.0±4.8 years vs. 28.5±4.1 years; t-test, p = 0.03). The groups did not differ in terms of obstetric characteristics. Our findings suggest that patients with PPD symptomatology may be more likely to exhibit soft bipolarity features as compared with non-depressed women.

  11. Psychedelics in the treatment of unipolar mood disorders: a systematic review.

    Science.gov (United States)

    Rucker, James Jh; Jelen, Luke A; Flynn, Sarah; Frowde, Kyle D; Young, Allan H

    2016-12-01

    Unipolar mood disorders, including major depressive disorder and persistent depressive disorder (dysthymia), confer high rates of disability and mortality and a very high socioeconomic burden. Current treatment is suboptimal in most cases and there is little of note in the pharmaceutical development pipeline. The psychedelic drugs, including lysergic acid diethylamide and psilocybin, were used extensively in the treatment of mood disorders, and other psychiatric conditions, before their prohibition in the late 1960s. They are relatively safe when used in medically controlled environments, with no reported risk of dependence. Here, we present a systematic review of published clinical treatment studies using psychedelics in patients with broadly defined UMD, and consider their place in psychiatry. Whilst all of the included studies have methodological shortcomings, of 423 individuals in 19 studies, 335 (79.2%) showed clinician-judged improvement after treatment with psychedelics. A recently completed pilot study in the UK favours the use of psilocybin with psychological support in treatment resistant depressive disorder. The evidence overall strongly suggests that psychedelics should be re-examined in modern clinical trials for their use in unipolar mood disorders and other non-psychotic mental health conditions. © The Author(s) 2016.

  12. Postpartum depression: bipolar or unipolar? Analysis of 434 Polish postpartum women

    Directory of Open Access Journals (Sweden)

    Rafał R. Jaeschke

    Full Text Available Objective: To assess the prevalence of soft bipolar features in a sample of women with postpartum depressive symptoms, as well as to compare the sociodemographic and obstetric characteristics of subjects with bipolar or unipolar postpartum depressive symptomatology. Methods: Four hundred and thirty-four participants were enrolled in this cross-sectional study. Postpartum depression (PPD symptoms were assessed using the Edinburgh Postnatal Depression Scale (EPDS, while the Mood Disorder Questionnaire (MDQ was used to screen for bipolarity features. Results: Of the 434 participants, 66 (15.2% scored ≥ 13 points on the EPDS, thus fulfilling the screening criteria, and 103 scored ≥ 7 points on the MDQ. In comparison with non-depressed subjects, the women who scored positively on the EPDS were significantly more likely to exhibit symptoms of bipolar spectrum disorders (38 vs. 21%; chi-square test, p = 0.015. Women with bipolar PPD symptomatology were significantly younger than those exhibiting unipolar PPD symptoms (31.0±4.8 years vs. 28.5±4.1 years; t-test, p = 0.03. The groups did not differ in terms of obstetric characteristics. Conclusion: Our findings suggest that patients with PPD symptomatology may be more likely to exhibit soft bipolarity features as compared with non-depressed women.

  13. Clinical characteristics of bipolar vs. unipolar depression in preschool children: an empirical investigation.

    Science.gov (United States)

    Luby, Joan L; Belden, Andy C

    2008-12-01

    Despite retrospective reports of the onset of childhood bipolar disorder during the preschool period, few studies have investigated whether mania symptoms can be identified in preschoolers. A group of children with a cluster of mania symptoms that showed discriminant validity from other disruptive disorders was identified in a large preschool sample. These empirical data add to descriptive studies of mania in clinical preschool populations. An investigation of the characteristics of depression among putative bipolar preschoolers may inform the controversial nosologic questions that surround the diagnosis in this young age group. This study, conducted from 2002 to 2007, investigated major depressive disorder (MDD) symptoms and severity in preschoolers with a bipolar syndrome in comparison to those with unipolar MDD, identified by an age-appropriate structured psychiatric interview, the Preschool Age Psychiatric Assessment (based on DSM-IV). Twenty-one preschoolers were identified who met DSM-IV symptom criteria for bipolar I disorder and MDD and were compared to 54 preschoolers with unipolar MDD. The bipolar depressed preschoolers had significantly higher depression severity (p nosology of this early-onset disorder. Copyright 2008 Physicians Postgraduate Press, Inc.

  14. Bupropion and venlafaxine responders differ in pretreatment regional cerebral metabolism in unipolar depression.

    Science.gov (United States)

    Little, John T; Ketter, Terence A; Kimbrell, Tim A; Dunn, Robert T; Benson, Brenda E; Willis, Mark W; Luckenbaugh, David A; Post, Robert M

    2005-02-01

    Pretreatment functional brain imaging was examined for never-hospitalized outpatients with unipolar depression compared with control subjects in a crossover treatment trial involving bupropion or venlafaxine monotherapy. Patients (n = 20) with unipolar depression received baseline (medication-free) fluorine-18 deoxyglucose (FDG) positron emission tomography (PET) scan and then at least 6 weeks of bupropion or venlafaxine monotherapy in a single-blind crossover trial. Age-matched healthy control subjects (n = 20) also received baseline FDG PET scans. For each medication PET data from patients compared with control subjects was analyzed as a function of treatment response (defined as moderate to marked improvement on the Clinical Global Impression Scale). Treatment response rates were similar for buproprion (32%) and venlafaxine (33%). Compared with control subjects, responders but not nonresponders, to both drugs demonstrated frontal and left temporal hypometabolism. Selectively, compared with control subjects bupropion responders (n = 6) also had cerebellar hypermetabolism, whereas venlafaxine responders (n = 7) showed bilateral temporal and basal ganglia hypometabolism. These data suggest that pretreatment frontal and left temporal hypometabolism in never-hospitalized depressed outpatients compared with control subjects is linked to positive antidepressant response and that additional alterations in regional metabolism may be linked to differential responsivity to bupropion and venlafaxine monotherapy.

  15. Scaling Effect on Unipolar and Bipolar Resistive Switching of Metal Oxides

    Science.gov (United States)

    Yanagida, Takeshi; Nagashima, Kazuki; Oka, Keisuke; Kanai, Masaki; Klamchuen, Annop; Park, Bae Ho; Kawai, Tomoji

    2013-01-01

    Electrically driven resistance change in metal oxides opens up an interdisciplinary research field for next-generation non-volatile memory. Resistive switching exhibits an electrical polarity dependent “bipolar-switching” and a polarity independent “unipolar-switching”, however tailoring the electrical polarity has been a challenging issue. Here we demonstrate a scaling effect on the emergence of the electrical polarity by examining the resistive switching behaviors of Pt/oxide/Pt junctions over 8 orders of magnitudes in the areas. We show that the emergence of two electrical polarities can be categorised as a diagram of an electric field and a cell area. This trend is qualitatively common for various oxides including NiOx, CoOx, and TiO2-x. We reveal the intrinsic difference between unipolar switching and bipolar switching on the area dependence, which causes a diversity of an electrical polarity for various resistive switching devices with different geometries. This will provide a foundation for tailoring resistive switching behaviors of metal oxides. PMID:23584551

  16. Tunable magnetism on the lateral mesoscale by post-processing of Co/Pt heterostructures

    Directory of Open Access Journals (Sweden)

    Oleksandr V. Dobrovolskiy

    2015-04-01

    Full Text Available Controlling magnetic properties on the nanometer-scale is essential for basic research in micro-magnetism and spin-dependent transport, as well as for various applications such as magnetic recording, imaging and sensing. This has been accomplished to a very high degree by means of layered heterostructures in the vertical dimension. Here we present a complementary approach that allows for a controlled tuning of the magnetic properties of Co/Pt heterostructures on the lateral mesoscale. By means of in situ post-processing of Pt- and Co-based nano-stripes prepared by focused electron beam induced deposition (FEBID we are able to locally tune their coercive field and remanent magnetization. Whereas single Co-FEBID nano-stripes show no hysteresis, we find hard-magnetic behavior for post-processed Co/Pt nano-stripes with coercive fields up to 850 Oe. We attribute the observed effects to the locally controlled formation of the CoPt L10 phase, whose presence has been revealed by transmission electron microscopy.

  17. Illumination intensity dependent photoresponse of ultra-thin ZnO/graphene/ZnO heterostructure

    Science.gov (United States)

    Dusza, M.; Granek, F.; Strek, W.

    2017-12-01

    A heterostructure of zinc oxide (ZnO) and single layer graphene is fabricated by sandwiching a transferred graphene between two thin ZnO films (∼20 nm each). ZnO thin films were grown using decomposition of Zn(acac)2 and spin-coating technique. Graphene transfer route with PMMA temporary carrier and metal etching process was used to transfer high quality commercial graphene from copper foil on the zinc oxide surface on glass. This novel and ultra-thin heterostructure (∼40 nm) is sensitive for UV illumination and works as a photodetector (PD). In this device, both positive and negative photoconductivity (PC) were observed depends on illumination intensity and spectrum of incident light. Relatively long response and recovery times obtained in ZnO/G/ZnO structure are related to the metastable defect states of ZnO and its interfaces with graphene and/or silver contacts. The obtained results show that the transferred single layer graphene sheet between thin ZnO films could be a novel route for improvement properties this low-cost metal oxide.

  18. The effect of exchange interaction on quasiparticle Landau levels in narrow-gap quantum well heterostructures.

    Science.gov (United States)

    Krishtopenko, S S; Gavrilenko, V I; Goiran, M

    2012-04-04

    Using the 'screened' Hartree-Fock approximation based on the eight-band k·p Hamiltonian, we have extended our previous work (Krishtopenko et al 2011 J. Phys.: Condens. Matter 23 385601) on exchange enhancement of the g-factor in narrow-gap quantum well heterostructures by calculating the exchange renormalization of quasiparticle energies, the density of states at the Fermi level and the quasiparticle g-factor for different Landau levels overlapping. We demonstrate that exchange interaction yields more pronounced Zeeman splitting of the density of states at the Fermi level and leads to the appearance of peak-shaped features in the dependence of the Landau level energies on the magnetic field at integer filling factors. We also find that the quasiparticle g-factor does not reach the maximum value at odd filling factors in the presence of large overlapping of spin-split Landau levels. We advance an argument that the behavior of the quasiparticle g-factor in weak magnetic fields is defined by a random potential of impurities in narrow-gap heterostructures. © 2012 IOP Publishing Ltd

  19. Trilayer TMDC Heterostructures for MOSFETs and Nanobiosensors

    Science.gov (United States)

    Datta, Kanak; Shadman, Abir; Rahman, Ehsanur; Khosru, Quazi D. M.

    2017-02-01

    Two dimensional materials such as transition metal dichalcogenides (TMDC) and their bi-layer/tri-layer heterostructures have become the focus of intense research and investigation in recent years due to their promising applications in electronics and optoelectronics. In this work, we have explored device level performance of trilayer TMDC heterostructure (MoS2/MX2/MoS2; M = Mo or, W and X = S or, Se) metal oxide semiconductor field effect transistors (MOSFETs) in the quantum ballistic regime. Our simulation shows that device `on' current can be improved by inserting a WS2 monolayer between two MoS2 monolayers. Application of biaxial tensile strain reveals a reduction in drain current which can be attributed to the lowering of carrier effective mass with increased tensile strain. In addition, it is found that gate underlap geometry improves electrostatic device performance by improving sub-threshold swing. However, increase in channel resistance reduces drain current. Besides exploring the prospect of these materials in device performance, novel trilayer TMDC heterostructure double gate field effect transistors (FETs) are proposed for sensing Nano biomolecules as well as for pH sensing. Bottom gate operation ensures these FETs operating beyond Nernst limit of 59 mV/pH. Simulation results found in this work reveal that scaling of bottom gate oxide results in better sensitivity while top oxide scaling exhibits an opposite trend. It is also found that, for identical operating conditions, proposed TMDC FET pH sensors show super-Nernst sensitivity indicating these materials as potential candidates in implementing such sensor. Besides pH sensing, all these materials show high sensitivity in the sub-threshold region as a channel material in nanobiosensor while MoS2/WS2/MoS2 FET shows the least sensitivity among them.

  20. Antimonide Heterostructure Nanowires - Growth, Physics and Devices

    OpenAIRE

    Borg, Mattias

    2012-01-01

    This thesis investigates the growth and application of antimonide heterostructure nanowires for low-power electronics. In the first part of the thesis, GaSb, InSb and InAsSb nanowire growth is presented, and the distinguishing features of the growth are described. It is found that the presence of Sb results in more than 50 at. % group-III concentration in the Au seed particle on top of the nanowires. It is further concluded that the effective V/III ratio inside the seed particle is reduced co...

  1. Exciton broadening in WS2/graphene heterostructures

    Science.gov (United States)

    Hill, Heather M.; Rigosi, Albert F.; Raja, Archana; Chernikov, Alexey; Roquelet, Cyrielle; Heinz, Tony F.

    2017-11-01

    We have used optical spectroscopy to observe spectral broadening of WS2 exciton reflectance peaks in heterostructures of monolayer WS2 capped with mono- to few-layer graphene. The broadening is found to be similar for the A and B excitons and on the order of 5-10 meV. No strong dependence on the number of graphene layers was observed within experimental uncertainty. The broadening can be attributed to charge- and energy-transfer processes between the two materials, providing an observed lower bound for the corresponding time scales of 65 fs.

  2. Temperature-controlled colossal magnetoresistance and perfect spin Seebeck effect in hybrid graphene/boron nitride nanoribbons.

    Science.gov (United States)

    Zhu, Lin; Li, Ruimin; Yao, Kailun

    2017-02-01

    Thermal spin transport properties of graphene and hexagonal boron nitride nanoribbon heterojunctions have been investigated using density functional theory calculations combined with the Keldysh nonequilibrium Green's function approach. The results showed that the perfect spin Seebeck effect and analogy negative differential thermoelectric resistance occurred in the device under a temperature difference without a gate or bias voltage. An intriguing thermally induced colossal magnetoresistance without gate regulation was also observed, which can be switched between a positive and negative value with temperature control. It was also found that the unit number of zigzag graphene nanoribbons and boron nitride nanoribbons can tune the electronic band structure and the energy gap of the heterostructure, and then modulate the thermal spin transport properties. The results suggest that graphene and hexagonal boron nitride nanoribbon heterostructures may have potential applications in graphene-based nanodevices.

  3. Fabrication of MgFe2O4/MoS2 Heterostructure Nanowires for Photoelectrochemical Catalysis.

    Science.gov (United States)

    Fan, Weiqiang; Li, Meng; Bai, Hongye; Xu, Dongbo; Chen, Chao; Li, Chunfa; Ge, Yilin; Shi, Weidong

    2016-02-16

    A novel one-dimensional MgFe2O4/MoS2 heterostructure has been successfully designed and fabricated. The bare MgFe2O4 was obtained as uniform nanowires through electrospinning, and MoS2 thin film appeared on the surface of MgFe2O4 after further chemical vapor deposition. The structure of the MgFe2O4/MoS2 heterostructure was systematic investigated by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectrometry (XPS), and Raman spectra. According to electrochemical impedance spectroscopy (EIS) results, the MgFe2O4/MoS2 heterostructure showed a lower charge-transfer resistance compared with bare MgFe2O4, which indicated that the MoS2 played an important role in the enhancement of electron/hole mobility. MgFe2O4/MoS2 heterostructure can efficiently degrade tetracycline (TC), since the superoxide free-radical can be produced by sample under illumination due to the active species trapping and electron spin resonance (ESR) measurement, and the optimal photoelectrochemical degradation rate of TC can be achieved up to 92% (radiation intensity: 47 mW/cm(2), 2 h). Taking account of its unique semiconductor band gap structure, MgFe2O4/MoS2 can also be used as an photoelectrochemical anode for hydrogen production by water splitting, and the hydrogen production rate of MgFe2O4/MoS2 was 5.8 mmol/h·m(2) (radiation intensity: 47 mW/cm(2)), which is about 1.7 times that of MgFe2O4.

  4. Auger recombination in {GaSb}/{AlSb} multi quantum well heterostructures

    Science.gov (United States)

    Zielinski, E.; Schweizer, H.; Griffiths, G.; Kroemer, H.; Subbanna, S.

    The experimental determination of Auger coefficients in {GaSb}/{AlSb} multi quantum well heterostructures is reported for the first time. The luminescence at E g and E g+ Δ0, recorded under the same experimental conditions, is used to monitor the carrier recombination channels. A quantitative determination of the recombination coefficients is achieved applying coupled carrier rate equations for the conduction and the valence subbands including the split-off valence band. Information on the actual carrier density is obtained by line shape analysis of the E g-emission. Two dimensional carrier densities up to 10 12cm -2 are determined. Auger coefficients exhibit a pronounced well width dependence: above 100Å C ˜- 4·10 -27s -1cm 6 whereas at 50Å values are 10 times smaller. No resonance of the Auger recombination is observed tuning the band gap energy over the spin-orbit splitting with temperature.

  5. Seeking the Dirac cones in the MoS2/WSe2 van der Waals heterostructure

    Science.gov (United States)

    Li, Qianze; Tang, Liangpo; Zhang, Caixin; Wang, Dan; Chen, Qin-Jun; Feng, Ye-Xin; Tang, Li-Ming; Chen, Ke-Qiu

    2017-10-01

    Ab initio calculations show that the bandgap of MoS2-WSe2 heterostructures can be significantly tuned by thickness engineering, perpendicular electric fields, and forming spin-valley coupling Dirac cones at the K and K ' valleys. The intrinsic band structure of the MoS2-WSe2 heterobilayer is found to be a direct bandgap, in which the conduction band minimum is located at the MoS2 layer, but the valence band maximum lies in the WSe2 layer, forming a type-II band alignment, which can be changed easily into type-I band alignment by applying perpendicular electric fields. The special dispersion relation like the Dirac cone and each of these band alignments have particular applications in enabling different varieties of devices.

  6. Positive magnetoresistance in Co40Fe40B20/SiO2/Si heterostructure

    KAUST Repository

    Zhang, Y.

    2016-07-20

    Current-perpendicular-to-plane electronic transport properties and magnetoresistance of amorphous Co40Fe40B20/SiO2/Si heterostructures are investigated systematically. A backward diode-like rectifying behavior was observed due to the formation of a Schottky barrier between Co40Fe40B20 and Si. The junction resistance shows a metal-insulator transition with decreasing temperature in both the forward and reverse ranges. A large positive magnetoresistance (MR) of ∼2300% appears at 200 K. The positive MR can be attributed to the magnetic-field-controlled impact ionization process of carriers. MR shows a temperature-peak-type character under a constant bias current, which is related to the spin-dependent barrier in the Si near the interface. © CopyrightEPLA, 2016.

  7. Quantized conductance doubling and hard gap in a two-dimensional semiconductor-superconductor heterostructure

    DEFF Research Database (Denmark)

    Kjærgaard, Morten; Nichele, F; Suominen, Henri Juhani

    2016-01-01

    topological matter is by coupling a 2D electron gas with strong spin-orbit interaction to an s-wave superconductor. Previous efforts along these lines have been adversely affected by interface disorder and unstable gating. Here we show measurements on a gateable InGaAs/InAs 2DEG with patterned epitaxial Al......Coupling a two-dimensional (2D) semiconductor heterostructure to a superconductor opens new research and technology opportunities, including fundamental problems in mesoscopic superconductivity, scalable superconducting electronics, and new topological states of matter. One route towards......, yielding devices with atomically pristine interfaces between semiconductor and superconductor. Using surface gates to form a quantum point contact (QPC), we find a hard superconducting gap in the tunnelling regime. When the QPC is in the open regime, we observe a first conductance plateau at 4e(2)/h...

  8. Implicit and explicit self-associations in bipolar disorder : A comparison with healthy controls and unipolar depressive disorder

    NARCIS (Netherlands)

    Jabben, Nienke; de Jong, Peter J.; Kupka, Ralph W.; Glashouwer, Klaske A.; Nolen, Willem A.; Penninx, Brenda W. J. H.

    2014-01-01

    According to cognitive theory, negative self-schemas are involved in the occurrence of depression. Whereas implicit depressive self-associations have been found in unipolar depression, it is unknown whether impaired associations with regard to the self are also involved in Bipolar Disorder (BD).

  9. Spin-orbit coupling and anomalous Josephson effect in nanowires.

    Science.gov (United States)

    Campagnano, G; Lucignano, P; Giuliano, D; Tagliacozzo, A

    2015-05-27

    A superconductor-semiconducting nanowire-superconductor heterostructure in the presence of spin-orbit coupling and magnetic field can support a supercurrent even in the absence of phase difference between the superconducting electrodes. We investigate this phenomenon—the anomalous Josephson effect—employing a model capable of describing many bands in the normal region. We discuss the geometrical and symmetry conditions required to have a finite anomalous supercurrent, and in particular we show that this phenomenon is enhanced when the Fermi level is located close to a band opening in the normal region.

  10. Spin-electromagnetic waves in planar multiferroic multilayers

    Science.gov (United States)

    Nikitin, Andrey A.; Ustinov, Alexey B.; Vitko, Vitalii V.; Nikitin, Alexey A.; Kondrahov, Alexandr V.; Pirro, P.; Lähderanta, E.; Kalinikos, Boris A.; Hillebrands, B.

    2017-07-01

    A general electrodynamic theory is developed for dispersion characteristics of spin-electromagnetic waves (SEWs) propagating in multiferroic multilayers. The derivation is based on the full set of Maxwell's equations taking into account retardation effects. The multilayers are considered to be composed of an infinite number of ferrite and ferroelectric layers having arbitrary thicknesses, as well as arbitrary magnetic and electric parameters. As an example, spectra of SEWs are calculated and analyzed for a heterostructure containing two thin ferrite films separated by a thin ferroelectric film. An electric field tunability of the SEW dispersion characteristics at gigahertz frequencies is shown, providing an efficient control of SEW wave-numbers important for applications.

  11. Graphene antidot lattices: Designed defects and spin qubits

    DEFF Research Database (Denmark)

    Pedersen, Thomas; Flindt, Christian; Pedersen, Jesper Goor

    2008-01-01

    Antidot lattices, defined on a two-dimensional electron gas at a semiconductor heterostructure, are a well-studied class of man-made structures with intriguing physical properties. We point out that a closely related system, graphene sheets with regularly spaced holes ("antidots"), should display...... qubits. We present a detailed study of the energetics of periodic graphene antidot lattices, analyze the level structure of a single defect, calculate the exchange coupling between a pair of spin qubits, and identify possible avenues for further developments....

  12. Spin-orbit coupling, electron transport and pairing instabilities in two-dimensional square structures

    Energy Technology Data Exchange (ETDEWEB)

    Kocharian, Armen N. [Department of Physics, California State University, Los Angeles, CA 90032 (United States); Fernando, Gayanath W.; Fang, Kun [Department of Physics, University of Connecticut, Storrs, Connecticut 06269 (United States); Palandage, Kalum [Department of Physics, Trinity College, Hartford, Connecticut 06106 (United States); Balatsky, Alexander V. [AlbaNova University Center Nordita, SE-106 91 Stockholm (Sweden)

    2016-05-15

    Rashba spin-orbit effects and electron correlations in the two-dimensional cylindrical lattices of square geometries are assessed using mesoscopic two-, three- and four-leg ladder structures. Here the electron transport properties are systematically calculated by including the spin-orbit coupling in tight binding and Hubbard models threaded by a magnetic flux. These results highlight important aspects of possible symmetry breaking mechanisms in square ladder geometries driven by the combined effect of a magnetic gauge field spin-orbit interaction and temperature. The observed persistent current, spin and charge polarizations in the presence of spin-orbit coupling are driven by separation of electron and hole charges and opposite spins in real-space. The modeled spin-flip processes on the pairing mechanism induced by the spin-orbit coupling in assembled nanostructures (as arrays of clusters) engineered in various two-dimensional multi-leg structures provide an ideal playground for understanding spatial charge and spin density inhomogeneities leading to electron pairing and spontaneous phase separation instabilities in unconventional superconductors. Such studies also fall under the scope of current challenging problems in superconductivity and magnetism, topological insulators and spin dependent transport associated with numerous interfaces and heterostructures.

  13. Spin-orbit coupling, electron transport and pairing instabilities in two-dimensional square structures

    Directory of Open Access Journals (Sweden)

    Armen N. Kocharian

    2016-05-01

    Full Text Available Rashba spin-orbit effects and electron correlations in the two-dimensional cylindrical lattices of square geometries are assessed using mesoscopic two-, three- and four-leg ladder structures. Here the electron transport properties are systematically calculated by including the spin-orbit coupling in tight binding and Hubbard models threaded by a magnetic flux. These results highlight important aspects of possible symmetry breaking mechanisms in square ladder geometries driven by the combined effect of a magnetic gauge field spin-orbit interaction and temperature. The observed persistent current, spin and charge polarizations in the presence of spin-orbit coupling are driven by separation of electron and hole charges and opposite spins in real-space. The modeled spin-flip processes on the pairing mechanism induced by the spin-orbit coupling in assembled nanostructures (as arrays of clusters engineered in various two-dimensional multi-leg structures provide an ideal playground for understanding spatial charge and spin density inhomogeneities leading to electron pairing and spontaneous phase separation instabilities in unconventional superconductors. Such studies also fall under the scope of current challenging problems in superconductivity and magnetism, topological insulators and spin dependent transport associated with numerous interfaces and heterostructures.

  14. Photoresponse of Natural van der Waals Heterostructures.

    Science.gov (United States)

    Ray, Kyle; Yore, Alexander E; Mou, Tong; Jha, Sauraj; Smithe, Kirby K H; Wang, Bin; Pop, Eric; Newaz, A K M

    2017-06-27

    Van der Waals heterostructures consisting of two-dimensional materials offer a platform to obtain materials by design and are very attractive owing to unique electronic states. Research on 2D van der Waals heterostructures (vdWH) has so far been focused on fabricating individually stacked atomically thin unary or binary crystals. Such systems include graphene, hexagonal boron nitride, and members of the transition metal dichalcogenide family. Here we present our experimental study of the optoelectronic properties of a naturally occurring vdWH, known as franckeite, which is a complex layered crystal composed of lead, tin, antimony, iron, and sulfur. We present here that thin film franckeite (60 nm < d < 100 nm) behaves as a narrow band gap semiconductor demonstrating a wide-band photoresponse. We have observed the band-edge transition at ∼1500 nm (∼830 meV) and high external quantum efficiency (EQE ≈ 3%) at room temperature. Laser-power-resolved and temperature-resolved photocurrent measurements reveal that the photocarrier generation and recombination are dominated by continuously distributed trap states within the band gap. To understand wavelength-resolved photocurrent, we also calculated the optical absorption properties via density functional theory. Finally, we have shown that the device has a fast photoresponse with a rise time as fast as ∼1 ms. Our study provides a fundamental understanding of the optoelectronic behavior in a complex naturally occurring vdWH, and may pave an avenue toward developing nanoscale optoelectronic devices with tailored properties.

  15. (DARPA) Topologically Protected Quantum Information Processing In Spin-Orbit Compled Semiconductors

    Science.gov (United States)

    2013-12-17

    studied in detail the non-Abelian topological order and Majorana fermions (MFs) in a heterostructure consisting of both electron- and hole-doped spin...the absence of the gap closing signatures before the emergence of the MFs in the electron doped nanowires , and deducing alternative scenarios for the...alternative interpretations for the experiments. This necessitated proposing a true smoking-gun signature of MFs in semiconductor nanowires which we also

  16. Bipolar or Unipolar Hemiarthroplasty after Femoral Neck Fracture in the Geriatric Population

    Directory of Open Access Journals (Sweden)

    Egemen Ayhan

    2013-12-01

    Full Text Available Background: The choice of prosthesis in hemiarthroplasty is controversial for geriatric patients after femoral neck fracture. We hypothesised that selection criteria for unipolar or bipolar prostheses could be constructed based on factors affecting mortality. Aims: The aims of this retrospective study were: (1 to determine the factors affecting mortality of femoral neck fracture patients ≥65 years of age; (2 to compare patient mortality rates, radiological findings, and functional outcomes according to prosthesis type (unipolar or bipolar; and (3 to evaluate the persistence of inner bearing mobility of bipolar prostheses. Study Design: Retrospective comparative study. Methods: In total, 144 patients operated for hemiarthroplasty and aged ≥65 were included. We classified the patients into either unipolar or bipolar prosthesis groups. To reveal factors that affected mortality, age, sex, delay in surgery, and American Society of Anesthesiologists score were obtained from folders. Barthel Daily Living, Harris hip, and acetabular erosion scores were calculated and bipolar head movement was analysed for live patients. Results: One-year mortality was 31.94%. Age ≥75 (p=0.029, male sex (p=0.048, and delay in surgery ≥6 (p=0.004 were the patient characteristics that were related to increased mortality. There were no significant differences in sex, age, American Society of Anesthesiologists score, delay in surgery, mortality, or Barthel, Harris, acetabulum scores between the two groups. Twenty patients from each group were admitted for last follow-up. Bipolar head movement was preserved for 33.3% of patients. They were inactive patients with low Barthel and Harris scores. Conclusion: Although bipolar head movement was preserved in inactive patients, we suppose that this conferred no advantage to these patients, who could hardly walk. In this study, male patients, those aged ≥75 years, and those operated at ≥6 days had an increased risk of

  17. Right ventricular outflow tract high-density endocardial unipolar voltage mapping in patients with Brugada syndrome: evidence for electroanatomical abnormalities.

    Science.gov (United States)

    Letsas, Konstantinos P; Efremidis, Michael; Vlachos, Konstantinos; Georgopoulos, Stamatis; Karamichalakis, Nikolaos; Asvestas, Dimitrios; Valkanas, Kosmas; Korantzopoulos, Panagiotis; Liu, Tong; Sideris, Antonios

    2017-05-02

    Epicardial structural abnormalities at the right ventricular outflow tract (RVOT) may provide the arrhythmia substrate in Brugada syndrome (BrS). Electroanatomical endocardial unipolar voltage mapping is an emerging tool that accurately identifies epicardial abnormalities in different clinical settings. This study investigated whether endocardial unipolar voltage mapping of the RVOT detects electroanatomical abnormalities in patients with BrS. Ten asymptomatic patients (8 males, 34.5 ± 11.2 years) with spontaneous type 1 ECG pattern of BrS and negative late gadolinium enhancement-cardiac magnetic resonance imaging (LGE-c-MRI) underwent high-density endocardial electroanatomical mapping (>800 points). Using a cut-off of 1 mV and 4 mV for normal bipolar and unipolar voltage, respectively, derived from 20 control patients without structural heart disease established by LGE-c-MRI, the extend of low-voltage areas within the RVOT was estimated using a specific calculation software. The mean RVOT area presenting low-voltage bipolar signals in BrS patients was 3.4 ± 1.7 cm2 (range 1.5-7 cm2). A significantly greater area of abnormal unipolar signals was identified (12.6 ± 4.6 cm2 [range 7-22 cm2], P: 0.001). Both bipolar and unipolar electroanatomical abnormalities were mainly located at the free wall of the RVOT. The mean RVOT activation time was significantly prolonged in BrS patients compared to control population (86.4 ± 16.5 vs. 63.4 ± 9.7 ms, P voltage abnormalities that possibly reflect epicardial structural abnormalities are identified at the RVOT of BrS patients.

  18. RHIC SPIN FLIPPER

    Energy Technology Data Exchange (ETDEWEB)

    BAI,M.; ROSER, T.

    2007-06-25

    This paper proposes a new design of spin flipper for RHIC to obtain full spin flip with the spin tune staying at half integer. The traditional technique of using an rf dipole or solenoid as spin flipper to achieve full spin flip in the presence of full Siberian snake requires one to change the snake configuration to move the spin tune away from half integer. This is not practical for an operational high energy polarized proton collider like RHIC where beam lifetime is sensitive to small betatron tune change. The design of the new spin flipper as well as numerical simulations are presented.

  19. Al/Sb free InGaAs unipolar barrier infrared detectors

    Science.gov (United States)

    Uzgur, Fatih; Karaca, Utku; Kizilkan, Ekin; Kocaman, Serdar

    2017-02-01

    It is numerically shown that Al/Sb free InGaAs unipolar barrier detectors with superior performance compared to the conventional heterojunction detectors can be constructed. Compositionally graded layers provide the transition between the high bandgap InGaAs barrier and the lattice matched InGaAs absorber layers. In addition, the delta doped layers remove the valence band offset in order to block only majority carriers and allow unimpeded flow of minority carriers. More than one order of magnitude reduction in the dark current is observed while photocurrent remains nearly unchanged. Proposed barrier structure utilized in this study is not limited to short wave infrared (SWIR) and can be applied to a variety of materials operating in various infrared regions.

  20. More Resilience in Males with Probable Bipolar Depression than Probable Unipolar Depression among Korean Conscripts.

    Science.gov (United States)

    Seo, Ji-Yeong; Lee, Dawon; Lee, Dongyun; Cha, Boseok; Park, Chul-Soo; Kim, Bong-Jo; Lee, Cheol-Soon; Lee, So-Jin; Ahn, In-Young; Choi, Jae-Won

    2017-09-01

    This study investigated whether the resilience of males with probable bipolar depression (PBD) can be strengthened and compared it to that of males with probable unipolar depression (PUD). Prospective data for 198 participants (PBD: 66, PUD: 66, normal control: 66) were analyzed. The participants' resilience, bipolarity and severity of depressive symptoms were evaluated at baseline and after 5 weeks. Analysis of variance (ANOVA) and repeated measure ANOVA was performed for comparing resilience between three groups through a basic military training. The PBD group demonstrated more resilience than the PUD group at baseline. Participants with PBD became significantly more resilient than participants with PUD after 5 weeks (p<0.01, F=6.967, η2p=0.052). The study indicates that interventions that strengthen resilience need to be developed for males with PBD and that such interventions are more effective for males with PBD than PUD.

  1. Nonverbal memory tasks in early differential diagnosis of Alzheimer's disease and unipolar depression.

    Science.gov (United States)

    Contador, Israel; Fernandez-Calvo, Bernardino; Cacho, Jesus; Ramos, Francisco; Lopez-Rolon, Alex

    2010-10-01

    We examined whether there are selective deficits in early-stage Alzheimer's disease (AD; n = 27) and in unipolar depression (UD; n = 17) patients on recall and recognition of spatial and visual components of nonverbal memory (NVM) and whether the two groups can be differentiated based on their performance on such tasks. We also investigated which NVM measures had the best discrimination power. We tested spatial, visuospatial, and visuoconstructive abilities in AD and UD patients. AD patients' scores on NVM tasks were significantly lower than those of healthy subjects (HS; n = 30) and consistently lower than those of the UD group. Z-scores suggested that AD patients suffered from a generalized impairment. Clear differences between AD and UD patients were found on abstract design tasks.

  2. EVALUATION OF VARIOUS UNIPOLAR MULTICARRIER PWM STRATEGIES FOR FIVE LEVEL FLYING CAPACITOR INVERTER

    Directory of Open Access Journals (Sweden)

    B. SHANTHI

    2012-06-01

    Full Text Available This paper presents the comparison of unipolar multicarrier Pulse Width Modulation (PWM techniques for the Flying Capacitor Multi Level Inverter (FCMLI. Due to switch combination redundancies, there are certain degrees of freedom to generate the five level AC output voltage. This paper presents the use of Control Freedom Degree (CFD combination. The effectiveness of the PWM strategies developed using CFD are demonstrated by simulation and experimentation. The results indicate that the multilevel inverter triggered by the developed USHPWM strategy exhibits reduced harmonics. PWM strategies developed are implemented in real time using dSPACE/Real Time Interface (RTI. The simulation and experimental output closely match with each other validating the strategies presented.

  3. Suicide attempts and psychological risk factors in patients with bipolar and unipolar affective disorder.

    Science.gov (United States)

    Pawlak, Joanna; Dmitrzak-Węglarz, Monika; Skibińska, Maria; Szczepankiewicz, Aleksandra; Leszczyńska-Rodziewicz, Anna; Rajewska-Rager, Aleksandra; Maciukiewicz, Małgorzata; Czerski, Piotr; Hauser, Joanna

    2013-01-01

    Suicide is an important clinical problem in psychiatric patients. The highest risk of suicide attempts is noted in affective disorders. The aim of the study was looking for suicide risk factors among personality dimensions and value system in patients with diagnosis of unipolar and bipolar affective disorder (n=189 patients, n=101 controls). To establish the diagnosis, we used SCID (Structured clinical interview for diagnostic and statistical manual of mental disorders, fourth edition) questionnaire, TCI (Temperament and Character Inventory) questionnaire and Value Survey--to assess the personality. The main limitations of the study are number of participants, lack of data about stressful life events and treatment with lithium. Novelty seeking and harm avoidance dimensions constituted suicide attempt risk factors in the group of patients with affective disorders. Protective role of cooperativeness was discovered. Patients with and without suicide attempt in lifetime history varied in self-esteem position in Value Survey. Copyright © 2013 Elsevier Inc. All rights reserved.

  4. Hierarchical personality traits and the distinction between unipolar and bipolar disorders.

    Science.gov (United States)

    Quilty, Lena C; Pelletier, Marianne; Deyoung, Colin G; Michael Bagby, R

    2013-05-01

    The association between personality and psychopathology can provide an insight into the structure of mental disorders and the shared etiology and pathophysiology underlying diagnoses with overlapping symptomatology. The majority of personality-psychopathology research pertinent to the mood disorders has focused upon traits at the higher-order levels of the personality hierarchy, rather than those at intermediate or lower levels. The purpose of the current investigation was to investigate whether unipolar and bipolar mood disorders, and the severity of depressive and manic symptoms, show differential associations with traits at multiple levels of the personality hierarchy. Participants (N=275; 63% women; mean age 42.95 years) with depressive disorders (n=139) and bipolar disorders (n=136), as assessed by the Structured Clinical Interview for DSM-IV, Axis I Disorders, Patient Version (SCID-I/P; First et al., 1995), completed the Hamilton Depression Rating Scale, Young Mania Scale, Revised NEO Personality Inventory and Big Five Aspect Scales. Results support the hypothesis that lower levels of the personality hierarchy provide additional differentiation of affective pathology. As compared to the widespread association of depressive symptoms with traits across the personality hierarchy, manic symptoms demonstrated more specific associations with traits at lower levels of the personality hierarchy. Patients with severe mania were excluded, thus the full range of mania is not represented in the current sample. These results support the use of lower-order personality traits to discriminate between unipolar versus bipolar mood disorder, and are consistent with changes proposed to the psychiatric nosology to increase diagnostic precision. Copyright © 2012 Elsevier B.V. All rights reserved.

  5. Acute Response to Unilateral Unipolar Electrical Carotid Sinus Stimulation in Patients With Resistant Arterial Hypertension.

    Science.gov (United States)

    Heusser, Karsten; Tank, Jens; Brinkmann, Julia; Menne, Jan; Kaufeld, Jessica; Linnenweber-Held, Silvia; Beige, Joachim; Wilhelmi, Mathias; Diedrich, André; Haller, Hermann; Jordan, Jens

    2016-03-01

    Bilateral bipolar electric carotid sinus stimulation acutely reduced muscle sympathetic nerve activity (MSNA) and blood pressure (BP) in patients with resistant arterial hypertension but is no longer available. The second-generation device uses a smaller unilateral unipolar disk electrode to reduce invasiveness while saving battery life. We hypothesized that the second-generation device acutely lowers BP and MSNA in treatment-resistant hypertensive patients. Eighteen treatment-resistant hypertensive patients (9 women/9 men; 53±11 years; 33±5 kg/m(2)) on stable medications have been included in the study. We monitored finger and brachial BP, heart rate, and MSNA. Without stimulation, BP was 165±31/91±18 mm Hg, heart rate was 75±17 bpm, and MSNA was 48±14 bursts per minute. Acute stimulation with intensities producing side effects that were tolerable in the short term elicited interindividually variable changes in systolic BP (-16.9±15.0 mm Hg; range, 0.0 to -40.8 mm Hg; P=0.002), heart rate (-3.6±3.6 bpm; P=0.004), and MSNA (-2.0±5.8 bursts per minute; P=0.375). Stimulation intensities had to be lowered in 12 patients to avoid side effects at the expense of efficacy (systolic BP, -6.3±7.0 mm Hg; range, 2.8 to -14.5 mm Hg; P=0.028 and heart rate, -1.5±2.3 bpm; P=0.078; comparison against responses with side effects). Reductions in diastolic BP and MSNA (total activity) were correlated (r(2)=0.329; P=0.025). In our patient cohort, unilateral unipolar electric baroreflex stimulation acutely lowered BP. However, side effects may limit efficacy. The approach should be tested in a controlled comparative study. © 2016 American Heart Association, Inc.

  6. Ge-Based Spin-Photodiodes for Room-Temperature Integrated Detection of Photon Helicity

    KAUST Repository

    Rinaldi, Christian

    2012-05-02

    Spin-photodiodes based on Fe/MgO/Ge(001) heterostructures are reported. These devices perform the room-temperature integrated electrical detection of the spin polarization of a photocurrent generated by circularly polarized photons with a wavelength of 1300 nm, for light pulses with intensity I 0 down to 200 μW. A forward and reverse-biased average photocurrent variation of 5.9% is measured for the complete reversal of the incident light helicity. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  7. Ge/Si core/multi shell heterostructure FETs

    Energy Technology Data Exchange (ETDEWEB)

    Picraux, Samuel T [Los Alamos National Laboratory; Dayeh, Shadi A [Los Alamos National Laboratory

    2010-01-01

    Concentric heterostructured materials provide numerous design opportunities for engineering strain and interfaces, as well as tailoring energy band-edge combinations for optimal device performance. Key to the realization of such novel device concepts is the complete understanding and full control over their growth, crystal structure, and hetero-epitaxy. We report here on a new route for synthesizing Ge/Si core/multi-shell heterostructure nanowires that eliminate Au seed diffusion on the nanowire sidewalls by engineering the interface energy density difference. We show that such control over core/shell synthesis enable experimental realization of heterostructure FET devices beyond those available in the literature with enhanced transport characteristics. We provide a side-by-side comparison on the transport properties of Ge/Si core/multi-shell nanowires grown with and without Au diffusion and demonstrate heterostructure FETs with drive currents that are {approx} 2X higher than record results for p-type FETs.

  8. Engineering charge transport by heterostructuring solution-processed semiconductors

    Science.gov (United States)

    Voznyy, Oleksandr; Sutherland, Brandon R.; Ip, Alexander H.; Zhitomirsky, David; Sargent, Edward H.

    2017-06-01

    Solution-processed semiconductor devices are increasingly exploiting heterostructuring — an approach in which two or more materials with different energy landscapes are integrated into a composite system. Heterostructured materials offer an additional degree of freedom to control charge transport and recombination for more efficient optoelectronic devices. By exploiting energetic asymmetry, rationally engineered heterostructured materials can overcome weaknesses, augment strengths and introduce emergent physical phenomena that are otherwise inaccessible to single-material systems. These systems see benefit and application in two distinct branches of charge-carrier manipulation. First, they influence the balance between excitons and free charges to enhance electron extraction in solar cells and photodetectors. Second, they promote radiative recombination by spatially confining electrons and holes, which increases the quantum efficiency of light-emitting diodes. In this Review, we discuss advances in the design and composition of heterostructured materials, consider their implementation in semiconductor devices and examine unexplored paths for future advancement in the field.

  9. Magnetic Heterostructures Advances and Perspectives in Spinstructures and Spintransport

    CERN Document Server

    Bader, Samuel D

    2008-01-01

    Magnetic heterostructures constitute an important field in magnetism and nanotechnology, which has developed over the past fifteen years due to important advances in epitaxial- growth techniques and lithographic processes. Magnetic heterostructures combine different physical properties which do not exist in nature. Examples are semiconductors/ferromagnets, superconductors/ferromagnets, and ferromagnets/antiferromagnets. These combinations display rich and novel physical properties different from those that exit in any single one of them. Interlayer exchange coupling, exchange bias, proximity effects, giant magneto-resistance, tunneling magneto-resistance, spininjection and spintransport are examples of new physical phenomena that rely on the combination of different materials layers. Since the literature on magnetic heterostructures is widely spread and highly specialized, the situation calls for a book that provides an overview of the basics and the state of the art of magnetic heterostructures. These contri...

  10. Polaronic Transport Induced by Competing Interfacial Magnetic Order in a La_{0.7}Ca_{0.3}MnO_{3}/BiFeO_{3} Heterostructure

    Directory of Open Access Journals (Sweden)

    Y. M. Sheu

    2014-04-01

    Full Text Available Using ultrafast optical spectroscopy, we show that polaronic behavior associated with interfacial antiferromagnetic order is likely the origin of tunable magnetotransport upon switching the ferroelectric polarity in a La_{0.7}Ca_{0.3}MnO_{3}/BiFeO_{3} (LCMO/BFO heterostructure. This is revealed through the difference in dynamic spectral weight transfer between LCMO and LCMO/BFO at low temperatures, which indicates that transport in LCMO/BFO is polaronic in nature. This polaronic feature in LCMO/BFO decreases in relatively high magnetic fields due to the increased spin alignment, while no discernible change is found in the LCMO film at low temperatures. These results thus shed new light on the intrinsic mechanisms governing magnetoelectric coupling in this heterostructure, potentially offering a new route to enhancing multiferroic functionality.

  11. Decoherence dynamics of a single spin versus spin ensemble

    NARCIS (Netherlands)

    Dobrovitski, V.V.; Feiguin, A.E.; Awschalom, D.D.; Hanson, R.

    2008-01-01

    We study decoherence of central spins by a spin bath, focusing on the difference between measurement of a single central spin and measurement of a large number of central spins (as found in typical spin-resonance experiments). For a dilute spin bath, the single spin demonstrates Gaussian

  12. Theory for Spin Selective Andreev Re ection in Vortex Core of Topological Superconductor: Majorana Zero Modes on Spherical Surface and Application to Spin Polarized Scanning Tunneling Microscope Probe

    Science.gov (United States)

    Zhang, Fu-Chun; Hu, Lun-Hui; Li, Chuang; Xu, Dong-Hui; Zhou, Yi

    Majorana zero modes (MZMs) have been predicted to exist in the topological insulator (TI)/superconductor (SC) heterostructure. Recent spin polarized scanning tunneling microscope(STM) experiment has observed spin-polarization dependence of the zero bias differential tunneling conductance at the center of vortex core. Here we consider a helical electron system described by a Rashba spin orbit coupling Hamiltonian on a spherical surface with a s-wave superconducting pairing due to proximity effect. We examine in-gap excitations of a pair of vortices with one at the north pole and the other at the south pole. While the MZM is not a spin eigenstate, the spin wavefunction of the MZM at the center of the vortex core, r = 0, is parallel to the magnetic field, and the local Andreev reflection of the MZM is spin selective, namely occurs only when the STM tip has the spin polarization parallel to the magnetic field, similar to the case in 1-dimensional nanowire. The total local differential tunneling conductance consists of the normal term proportional to the local density of states and an additional term arising from the Andreev reflection. We apply our theory to examine the recently reported spin-polarized STM experiments and show good agreement with the experiments

  13. Organic heterostructures deposited by MAPLE on AZO substrate

    Science.gov (United States)

    Socol, M.; Preda, N.; Stanculescu, A.; Breazu, C.; Florica, C.; Stanculescu, F.; Iftimie, S.; Girtan, M.; Popescu-Pelin, G.; Socol, G.

    2017-09-01

    Organic heterostructures based on poly(3-hexylthiophene) (P3HT) and fullerene (C60) as blends or multilayer were deposited on Al:ZnO (AZO) by Matrix-Assisted Pulsed Laser Evaporation (MAPLE) technique. The AZO layers were obtained by Pulsed Laser Deposition (PLD) on glass substrate, the high quality of the films being reflected by the calculated figure of merit. The organic heterostructures were investigated from morphological, optical and electrical point of view by atomic force microscopy (AFM), UV-vis spectroscopy, photoluminescence (PL) and current-voltage (I-V) measurements, respectively. The increase of the C60 content in the blend heterostructure has as result a high roughness. Compared with the multilayer heterostructure, those based on blends present an improvement in the electrical properties. Under illumination, the highest current value was recorded for the heterostructure based on the blend with the higher C60 amount. The obtained results showed that MAPLE is a useful technique for the deposition of the organic heterostructures on AZO as transparent conductor electrode.

  14. Giant spin-charge conversion driven by nanoscopic particles of Ag in Pt

    Science.gov (United States)

    Alves-Santos, O.; Silva, E. F.; Gamino, M.; Cunha, R. O.; Mendes, J. B. S.; Rodríguez-Suárez, R. L.; Rezende, S. M.; Azevedo, A.

    2017-08-01

    We report the observation of a giant enhancement in the interconversion efficiency between spin current and charge current by the spin Hall effect made possible with the use of nanoscopic structures of Ag in a Pt layer. We fabricate heterostructures of yttrium iron garnet (YIG)/Pt, in which nanoparticles of Ag were grown in the midplane of the Pt layer. These nanostructures serve as nanoscopic molds that enhance the local spin orbit coupling by means of the Rashba effect at the Pt-Ag interfaces. The effective spin Hall angle in YIG/[Pt (3 nm)-Ag (9 nm)]/Pt (3 nm) is determined to be in the range of 27-40%, which is about one order of magnitude larger than the spin Hall angle of pure Pt, typically in the range of 2-8%. The results were confirmed by means of three different experimental techniques, namely spin pumping effect, spin Seebeck effect, and spin Hall magnetoresistance. We believe that this important discovery will contribute to advance the development of spin-based technology.

  15. Quantum and field effects of oxide heterostructures

    DEFF Research Database (Denmark)

    Trier, Felix

    . In these multi-plexed devices, several inputs aretranslated into several outputs through the multiple physical functionalities.A highly prominent example of such an oxide interface is the one between LaAlO3 and SrTiO3. Although both LaAlO3 and SrTiO3 in the bulk are electrically insulating and non...... aspects of sample preparation will initially be covered. Here, the growth of amorphous-LaAlO3 on SrTiO3 will be addressed in a modified pulsed laser deposition setup. This is followed by an investigation of two high-electron mobility interfaces in SrTiO3-based heterostructures. Specifically...

  16. Magnetoelectric imaging of multiferroic heterostructures (Presentation Recording)

    Science.gov (United States)

    Ghidini, Massimo; Lesaine, Arnaud; Zhu, Bonan; Moya, Xavier; Yan, Wenjing; Crossley, Sam; Nair, Bhasi; Mansell, Rhodri; Cowburn, Russell P.; Barnes, Crispin H. W.; Kronast, Florian; Valencia, Sergio; Maccherozzi, Francesco; Dhesi, Sarnjeet S.; Mathur, Neil

    2015-09-01

    Electrical control of magnetism has been demonstrated in multiferroic compounds and ferromagnetic semiconductors, but electrical switching of a substantial net magnetization at room temperature has not been demonstrated in these materials. This goal has instead been achieved in heterostructures comprising ferromagnetic films in which electrically driven magnetic changes arise due to strain or exchange bias from ferroic substrates, or due to charge effects induced by a gate. However, previous work focused on electrical switching of an in-plane magnetization or involved the assistance of applied magnetic fields. In heterostructures made of juxtaposed ferroelectric and ferromagnetic layers, we have shown electrical control with no applied magnetic field of the perpendicular magnetization of small features [1] and of magnetic stripe domains patterns [2]. Here we investigate Ni81Fe19 films on ferroelectric substrates with and without buffer layers of Cu, whose presence precludes charge-mediated coupling. Ni81Fe19 has virtually zero magnetostriction, but sufficiently thin films show large magnetostriction, and thus, on increasing film thickness through the threshold for zero magnetostriction, we have seeked the crossover from charge- to strain-mediated coupling. We will then show that strain associated with the motion of 90°- ferroelectric domain walls in a BaTiO3 substrate, can switch the magnetization of an array of overlying single-domain Ni dots. [1] M. Ghidini, R. Pellicelli, J. L. Prieto, X. Moya, J. Soussi, J. Briscoe, S. Dunn and N. D. Mathur, Nature Communications 4 (2013) 1453. [2] M. Ghidini, F.Maccherozzi, X. Moya, L. C. Phillips, W.Yan, J. Soussi, N. Métallier, M.Vickers, , N. -J.Steinke, R. Mansell, C. H. W. Barnes, S. S. Dhesi, and N. D. Mathur, Adv. Mater.doi: 10.1002/adma.201404799 (2015).

  17. Dry-transferred CVD graphene for inverted spin valve devices

    Science.gov (United States)

    Drögeler, Marc; Banszerus, Luca; Volmer, Frank; Taniguchi, Takashi; Watanabe, Kenji; Beschoten, Bernd; Stampfer, Christoph

    2017-10-01

    Integrating high-mobility graphene grown by chemical vapor deposition (CVD) into spin transport devices is one of the key tasks in graphene spintronics. We use a van der Waals pick-up technique to transfer CVD graphene by hexagonal boron nitride (hBN) from the copper growth substrate onto predefined Co/MgO electrodes to build inverted spin valve devices. Two approaches are presented: (i) a process where the CVD-graphene/hBN stack is first patterned into a bar and then transferred by a second larger hBN crystal onto spin valve electrodes and (ii) a direct transfer of a CVD-graphene/hBN stack. We report record high spin lifetimes in CVD graphene of up to 1.75 ns at room temperature. Overall, the performances of our devices are comparable to devices fabricated from exfoliated graphene also revealing nanosecond spin lifetimes. We expect that our dry transfer methods pave the way towards more advanced device geometries not only for spintronic applications but also for CVD-graphene-based nanoelectronic devices in general where patterning of the CVD graphene is required prior to the assembly of final van der Waals heterostructures.

  18. Magnetization dynamics of imprinted non-collinear spin textures

    Energy Technology Data Exchange (ETDEWEB)

    Streubel, Robert, E-mail: r.streubel@ifw-dresden.de; Kopte, Martin; Makarov, Denys, E-mail: d.makarov@ifw-dresden.de [Institute for Integrative Nanosciences, IFW Dresden, 01069 Dresden (Germany); Fischer, Peter [Center for X-Ray Optics, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Physics Department, UC Santa Cruz, Santa Cruz, California 95064 (United States); Schmidt, Oliver G. [Institute for Integrative Nanosciences, IFW Dresden, 01069 Dresden (Germany); Material Systems for Nanoelectronics, Chemnitz University of Technology, 09107 Chemnitz (Germany)

    2015-09-14

    We study the magnetization dynamics of non-collinear spin textures realized via imprint of the magnetic vortex state in soft permalloy into magnetically hard out-of-plane magnetized Co/Pd nanopatterned heterostructures. Tuning the interlayer exchange coupling between soft- and hard-magnetic subsystems provides means to tailor the magnetic state in the Co/Pd stack from being vortex- to donut-like with different core sizes. While the imprinted vortex spin texture leads to the dynamics similar to the one observed for vortices in permalloy disks, the donut-like state causes the appearance of two gyrofrequencies characteristic of the early and later stages of the magnetization dynamics. The dynamics are described using the Thiele equation supported by the full scale micromagnetic simulations by taking into account an enlarged core size of the donut states compared to magnetic vortices.

  19. Periodic structure of spin-transfer current in ferromagnetic multilayers

    Energy Technology Data Exchange (ETDEWEB)

    Levin, Pavel [Mechanical Engineering Department, City College/CUNY, 138th St. at W. Convent Av., New York, NY 10031 (United States)]. E-mail: levinpavel@yahoo.com

    2007-01-01

    We show that the drift-diffusion mechanism in a normal-metal layer in combination with the resonance electron-magnon interactions at ferromagnet-normal interface of F-N-F heterostructure creates spatial instability modes and, out of these modes, a quasi-stable periodic structure of spin-transfer d.c. current can arise with certain channel step and step-to-radius ratio. The ferromagnetic resonance conditions determine spin-transfer current density. Independent nanooscillators creating intersecting arrays of channels can phase-lock on sub-micrometer distance, which depends on multilayer geometry and applied fields. By decreasing the layer thickness, the number of channels affected by each independent d.c.-current source and their radius may be diminished. Phase-locking of multiple independent nanooscillators can be used for enhancement of output power.

  20. High-Frequency Dynamics Modulated by Collective Magnetization Reversal in Artificial Spin Ice

    Energy Technology Data Exchange (ETDEWEB)

    Jungfleisch, Matthias B.; Sklenar, Joseph; Ding, Junjia; Park, Jungsik; Pearson, John E.; Novosad, Valentine; Schiffer, Peter; Hoffmann, Axel

    2017-12-01

    Spin-torque ferromagnetic resonance arises in heavy metal-ferromagnet heterostructures when an alternating charge current is passed through the bilayer stack. The methodology to detect the resonance is based on the anisotropic magnetoresistance, which is the change in the electrical resistance due to different orientations of the magnetization. In connected networks of ferromagnetic nanowires, known as artificial spin ice, the magnetoresistance is rather complex owing to the underlying collective behavior of the geometrically frustrated magnetic domain structure. Here, we demonstrate spin-torque ferromagnetic resonance investigations in a square artificial spin-ice system and correlate our observations to magneto-transport measurements. The experimental findings are described using a simulation approach that highlights the importance of the correlated dynamics response of the magnetic system. Our results open the possibility of designing reconfigurable microwave oscillators and magnetoresistive devices based on connected networks of nanomagnets.

  1. Ultra-low charge and spin noise in self-assembled quantum dots

    Science.gov (United States)

    Ludwig, Arne; Prechtel, Jonathan H.; Kuhlmann, Andreas V.; Houel, Julien; Valentin, Sascha R.; Warburton, Richard J.; Wieck, Andreas D.

    2017-11-01

    Self-assembled InxGa1-xAs quantum dots (QDs) are promising hosts for spin qubits with excellent coupling to photons. Nuclear spin and charge fluctuations lead to dephasing and limit the applicability of QDs as qubits. We show that charge noise can be minimized by high quality MBE growth of well-designed heterostructures yielding natural optical linewidths down to 1.15 μeV. To minimize the nuclear spin noise, one direction would be to reduce the wave function overlap with the nuclei. We show that this is indeed the case for a single hole spin in a QD that we embedded in the intrinsic region of an n-i-p-diode. For random nuclei, the heavy-hole limit is achieved down to neV energies, equivalent to dephasing times of microseconds.

  2. Spin-Mechatronics

    Science.gov (United States)

    Matsuo, Mamoru; Saitoh, Eiji; Maekawa, Sadamichi

    2017-01-01

    We investigate the interconversion phenomena between spin and mechanical angular momentum in moving objects. In particular, the recent results on spin manipulation and spin-current generation by mechanical motion are examined. In accelerating systems, spin-dependent gauge fields emerge, which enable the conversion from mechanical angular momentum into spins. Such a spin-mechanical effect is predicted by quantum theory in a non-inertial frame. Experiments which confirm the effect, i.e., the resonance frequency shift in nuclear magnetic resonance, the stray field measurement of rotating metals, and electric voltage generation in liquid metals, are discussed.

  3. Aseptic lymphocyte dominated vasculitis-associated lesion resulting from trunnion corrosion in a cobalt-chrome unipolar hemiarthroplasty.

    Science.gov (United States)

    Khair, M Michael; Nam, Denis; DiCarlo, Edward; Su, Edwin

    2013-01-01

    Most of the published descriptions of adverse soft tissue reactions that have been reported in the context of a metal-on-metal articulation have been in cases of total hip arthroplasty or resurfacing arthroplasty. Recently, several case reports have been published describing aseptic lymphocyte dominated vasculitis-associated lesions (ALVAL) in metal-on-polyethylene. To our knowledge, there has not been a description of a similar, aggressive reaction secondary to metal debris from the head-neck junction of a unipolar hemiarthroplasty component. In this case report, we describe a patient with a catastrophic failure of a unipolar hip hemiarthroplasty, secondary to aggressive osteolysis and an inflammatory mediated immunological reaction to metal debris. Copyright © 2013 Elsevier Inc. All rights reserved.

  4. In-Plane Crystallinity Effect on the Unipolar Resistance Switching Behavior of NiO Thin Film.

    Science.gov (United States)

    Kim, Il Tae; Hur, Jaehyun; Chae, Seung Chul

    2016-02-01

    We report on the resistance switching behavior of high quality NiO thin films grown on Pt(111)/SiOx/Si and Pt(111)/Al2O3 crystals. Polarity independent resistance switching, i.e., unipolar resistance switching exhibited a substrate crystallinity dependence during the resistance switching. The unipolar resistance switching was observed commonly in NiO film grown on both substrates. High resistance state of NiO thin film without in-plane crystallinity showed higher resistance than that of NiO films with in-plane crystallinity. The NiO thin film without in-plane crystallinity also required high set voltages for the resistance switching from high resistance state to low resistance state and showed nonlinear I-V characteristics at high voltage region before the resistance switching.

  5. The cumulative load of depressive illness is associated with cognitive function in the remitted state of unipolar depressive disorder

    DEFF Research Database (Denmark)

    Hasselbalch, BJ; Knorr, U; Hasselbalch, S G

    2013-01-01

    OBJECTIVE: To investigate whether the cumulative number, duration and subtypes (severity and presence of psychotic features) of previous episodes of depression in patients with unipolar depressive disorder in a remitted state are associated with decreased global cognitive function. METHODS: Via...... the Danish registers individuals between 40 and 80 years of age were identified: (1) patients with a diagnosis of unipolar disorder at their first discharge from a psychiatric hospital in the period 1994 to 2002, and (2) gender and age matched control individuals. The participants were assessed...... was associated with a decreased CAMCOG score adjusted for age, gender, education, premorbid IQ and residual depressive symptoms (B=-0.14, 95% C.I. (-0.26, -0.02), R(2)(adj)=0.31, P=.02). Significant associations were also found between CAMCOG score and the cumulative duration and total number of depressive...

  6. Unipolar resistive switching in metal oxide/organic semiconductor non-volatile memories as a critical phenomenon

    Energy Technology Data Exchange (ETDEWEB)

    Bory, Benjamin F.; Meskers, Stefan C. J., E-mail: s.c.j.meskers@tue.nl [Molecular Materials and Nanosystems and Institute for Complex Molecular Systems, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven (Netherlands); Rocha, Paulo R. F. [Instituto de Telecomunicações, Av. Rovisco, Pais, 1, 1049-001 Lisboa, Portugal and Universidade do Algarve, Campus de Gambelas, 8005-139 Faro (Portugal); Max-Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz (Germany); Gomes, Henrique L. [Instituto de Telecomunicações, Av. Rovisco, Pais, 1, 1049-001 Lisboa, Portugal and Universidade do Algarve, Campus de Gambelas, 8005-139 Faro (Portugal); Leeuw, Dago M. de [Max-Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz (Germany)

    2015-11-28

    Diodes incorporating a bilayer of an organic semiconductor and a wide bandgap metal oxide can show unipolar, non-volatile memory behavior after electroforming. The prolonged bias voltage stress induces defects in the metal oxide with an areal density exceeding 10{sup 17 }m{sup −2}. We explain the electrical bistability by the coexistence of two thermodynamically stable phases at the interface between an organic semiconductor and metal oxide. One phase contains mainly ionized defects and has a low work function, while the other phase has mainly neutral defects and a high work function. In the diodes, domains of the phase with a low work function constitute current filaments. The phase composition and critical temperature are derived from a 2D Ising model as a function of chemical potential. The model predicts filamentary conduction exhibiting a negative differential resistance and nonvolatile memory behavior. The model is expected to be generally applicable to any bilayer system that shows unipolar resistive switching.

  7. Determining the sign of exchange coupling in a chromia based perpendicular exchange bias heterostructure

    Science.gov (United States)

    Singh, Uday; Street, Mike; Echtenkamp, Will; Binek, Christian; Adenwalla, Shireen

    Exchange bias arises from the coupling at the AFM/FM interface and, has been observed and studied in a wide range of systems. A key property of exchange bias systems is the sign of the coupling between the ferromagnet spins and the interfacial antiferromagnet spins, which may be aligned either ferromagnetically (parallel) or antiferromagnetically (antiparallel). Antiferromagnetic exchange coupling is known to be the generic cause of positive exchange bias. Determining the sign of exchange coupling is straight forward in system where the coupling is weak and can be overcome by Zeeman energy on field -cooling. It is, however, a challenging task when the available magnetic field is low or the magnitude of the exchange coupling is high. Here, we present a technique to determine the sign of the exchange coupling using low fields. We measure the exchange bias field as a function of ferromagnet magnetization during field cooling and the resultant behavior of the exchange bias vs. the magnetization uniquely determines the sign of the coupling. We use this to measure the sign of the exchange coupling in a Cr2O3(300 nm)/Pd(0.5 nm)/[Co(0.3 nm)/Pd(1 nm)]3 heterostructure thin film system and verify our results with the conventional high field method. This work was supported by the National Science Foundation (NSF) through Grant No. DMR-1409622 and the Nebraska Materials Research Science and Engineering Center (MRSEC) (Grant No. DMR-1420645).

  8. Is there a difference in subjective experience of cognitive function in patients with unipolar disorder versus bipolar disorder?

    DEFF Research Database (Denmark)

    Miskowiak, Kamilla; Vinberg, Maj; Christensen, Ellen Magrethe

    2012-01-01

    Background: Cognitive dysfunction in unipolar disorder (UD) and bipolar disorder (BD) may persist into remission and affect psychosocial function. Executive and memory deficits during remission may be more pronounced in BD than UD. However, patients' subjective experience of cognitive difficulties...... at their initial consultation at the clinic. Results: Patients experienced mild to moderate cognitive impairment despite being in partial or full remission, but there were no differences in subjective difficulties between BD and UD. Subjective cognitive dysfunction was predicted by depression severity, anxiety...

  9. A Smart Shirt Made with Conductive Ink and Conductive Foam for the Measurement of Electrocardiogram Signals with Unipolar Precordial Leads

    OpenAIRE

    Yasunori Tada; Yusaku Amano; Tomonobu Sato; Shigeru Saito; Masahiro Inoue

    2015-01-01

    The Holter monitor is used to measure an electrocardiogram (ECG) signal while a subject moves. However, the Holter monitor is uncomfortable for the subject. Another method of measuring the ECG signal uses a smart shirt. We developed a smart shirt that has six electrodes on the chest and can measure a detailed ECG, obtained with unipolar precordial leads. The electrodes and wires of the shirt are made of conductive ink that is flexible and stretchable. The smart shirt is stretchable and fits t...

  10. Higher spin black holes

    National Research Council Canada - National Science Library

    Gutperle, Michael; Kraus, Per

    2011-01-01

    .... We find solutions that generalize the BTZ black hole and carry spin-3 charge. The black hole entropy formula yields a result for the asymptotic growth of the partition function at finite spin-3 chemical potential...

  11. Summary: symmetries and spin

    Energy Technology Data Exchange (ETDEWEB)

    Haxton, W.C. (Institute for Nuclear Theory, Department of Physcis, FM-15, University of Washington, Seattle, Washington 98195 (US))

    1989-05-01

    I discuss a number of the themes of the Symmetries and Spin session of the 8th International Symposium on High Energy Spin Physics: parity non-conservation, CP/T nonconservation, and tests of charge symmetry and charge independence.

  12. Dynamic nuclear spin polarization

    Energy Technology Data Exchange (ETDEWEB)

    Stuhrmann, H.B. [GKSS-Forschungszentrum Geesthacht GmbH (Germany)

    1996-11-01

    Polarized neutron scattering from dynamic polarized targets has been applied to various hydrogenous materials at different laboratories. In situ structures of macromolecular components have been determined by nuclear spin contrast variation with an unprecedented precision. The experiments of selective nuclear spin depolarisation not only opened a new dimension to structural studies but also revealed phenomena related to propagation of nuclear spin polarization and the interplay of nuclear polarisation with the electronic spin system. The observation of electron spin label dependent nuclear spin polarisation domains by NMR and polarized neutron scattering opens a way to generalize the method of nuclear spin contrast variation and most importantly it avoids precontrasting by specific deuteration. It also likely might tell us more about the mechanism of dynamic nuclear spin polarisation. (author) 4 figs., refs.

  13. Sample heterogeneity in unipolar depression as assessed by functional connectivity analyses is dominated by general disease effects.

    Science.gov (United States)

    Feder, Stephan; Sundermann, Benedikt; Wersching, Heike; Teuber, Anja; Kugel, Harald; Teismann, Henning; Heindel, Walter; Berger, Klaus; Pfleiderer, Bettina

    2017-11-01

    Combinations of resting-state fMRI and machine-learning techniques are increasingly employed to develop diagnostic models for mental disorders. However, little is known about the neurobiological heterogeneity of depression and diagnostic machine learning has mainly been tested in homogeneous samples. Our main objective was to explore the inherent structure of a diverse unipolar depression sample. The secondary objective was to assess, if such information can improve diagnostic classification. We analyzed data from 360 patients with unipolar depression and 360 non-depressed population controls, who were subdivided into two independent subsets. Cluster analyses (unsupervised learning) of functional connectivity were used to generate hypotheses about potential patient subgroups from the first subset. The relationship of clusters with demographical and clinical measures was assessed. Subsequently, diagnostic classifiers (supervised learning), which incorporated information about these putative depression subgroups, were trained. Exploratory cluster analyses revealed two weakly separable subgroups of depressed patients. These subgroups differed in the average duration of depression and in the proportion of patients with concurrently severe depression and anxiety symptoms. The diagnostic classification models performed at chance level. It remains unresolved, if subgroups represent distinct biological subtypes, variability of continuous clinical variables or in part an overfitting of sparsely structured data. Functional connectivity in unipolar depression is associated with general disease effects. Cluster analyses provide hypotheses about potential depression subtypes. Diagnostic models did not benefit from this additional information regarding heterogeneity. Copyright © 2017 Elsevier B.V. All rights reserved.

  14. Differential endorsement of suicidal ideation and attempt in bipolar versus unipolar depression: a testlet response theory analysis.

    Science.gov (United States)

    Weinstock, Lauren M; Strong, David; Uebelacker, Lisa A; Miller, Ivan W

    2016-08-01

    Published data concerning differences in suicide risk across the mood disorders spectrum remain mixed. The current study used testlet response theory methods to evaluate differences in the endorsement of suicidal ideation and attempt in an epidemiological sample of individuals with bipolar and unipolar depression. Participants with lifetime history of bipolar I (n=1154), bipolar II (n=494), and unipolar (n=5695) depression were drawn from the National Epidemiologic Survey on Alcohol and Related Conditions, which included 4 structured queries concerning suicidal ideation/attempt. We estimated differential item functioning between groups with a 2-pl parametric item response model. Endorsement of suicide items increased as a function of underlying depression severity. Equating for severity, endorsement of suicidal ideation and attempt was generally more frequent in bipolar versus unipolar depression, and in bipolar I versus bipolar II depression. Yet findings were not consistent across all suicide items, and differences were small in magnitude. The NESARC relied upon lifetime endorsement of suicide items, and suicide risk was only evaluated within the context of a major depressive episode. Thus, this study could not evaluate endorsement of suicide items within the context of (hypo)manic or mixed states. Although there were some group differences, patterns of item endorsement were more similar than different. These data support a transdiagnostic model of suicide that emphasizes underlying depression severity over mood disorder class. Copyright © 2016 Elsevier B.V. All rights reserved.

  15. Compliance current dependence of conversion between bipolar, unipolar, and threshold resistance switching in Mn3O4 films

    Directory of Open Access Journals (Sweden)

    Shuxiang Wu

    2015-08-01

    Full Text Available We report deterministic conversion between bipolar, unipolar and threshold resistance switching in Pt/Mn3O4/Pt memory devices via tuning compliance current. The conversion between bipolar and unipolar switching is reversible, while that between memory switching and threshold switching is irreversible. The nonvolatile bipolar resistance switching behaviors could be attributed to modification of Schottky barrier at Pt/Mn3O4 interface due to the migration of positively charged oxygen vacancies. With the increase of current, the incomplete filament formed in the set operation of bipolar switching could continue to grow and until completely form. The subsequent rupture and formation of filament consisting of oxygen vacancies under electric field are responsible for the unipolar resistance switching. Further increase of compliance current causes the volatile threshold switching behavior in the Pt/Mn3O4/Pt devices, which could be originated from formation and rupture of filament consisting of Mn ions due to the high Joule heat generated by large current.

  16. Removal of fine and ultrafine particles from indoor air environments by the unipolar ion emission

    Science.gov (United States)

    Uk Lee, Byung; Yermakov, Mikhail; Grinshpun, Sergey A.

    2004-09-01

    The continuous emission of unipolar ions was evaluated in order to determine its ability to remove fine and ultrafine particles from indoor air environments. The evolution of the indoor aerosol concentration and particle size distribution was measured in real time with the ELPI in a room-size (24.3 m3) test chamber where the ion emitter was operating. After the results were compared with the natural decay, the air cleaning factor was determined. The particle aerodynamic size range of ∼0.04-2 μm was targeted because it represents many bioaerosol agents that cause emerging diseases, as well as those that can be used for biological warfare or in the event of bioterrorism. The particle electric charge distribution (also measured in the test chamber with the ELPI) was rapidly affected by the ion emission. It was concluded that the corona discharge ion emitters (either positive or negative), which are capable of creating an ion density of 105-106 e± cm-3, can be efficient in controlling fine and ultrafine aerosol pollutants in indoor air environments, such as a typical office or residential room. At a high ion emission rate, the particle mobility becomes sufficient so that the particle migration results in their deposition on the walls and other indoor surfaces. Within the tested ranges of the particle size and ion density, the particles were charged primarily due to the diffusion charging mechanism. The particle removal efficiency was not significantly affected by the particle size, while it increased with increasing ion emission rate and the time of emission. The performance characteristics of three commercially available ionic air purifiers, which produce unipolar ions by corona discharge at relatively high emission rates, were evaluated. A 30-minute operation of the most powerful device among those tested resulted in the removal of about 97% of 0.1 μm particles and about 95% of 1 μm particles from the air in addition to the natural decay effect.

  17. Quantum Spin Liquids

    OpenAIRE

    Savary, Lucile; Balents, Leon

    2016-01-01

    Quantum spin liquids may be considered "quantum disordered" ground states of spin systems, in which zero point fluctuations are so strong that they prevent conventional magnetic long range order. More interestingly, quantum spin liquids are prototypical examples of ground states with massive many-body entanglement, of a degree sufficient to render these states distinct phases of matter. Their highly entangled nature imbues quantum spin liquids with unique physical aspects, such as non-local e...

  18. Spinning eggs and ballerinas

    Science.gov (United States)

    Cross, Rod

    2013-01-01

    Measurements are presented on the rise of a spinning egg. It was found that the spin, the angular momentum and the kinetic energy all decrease as the egg rises, unlike the case of a ballerina who can increase her spin and kinetic energy by reducing her moment of inertia. The observed effects can be explained, in part, in terms of rolling friction between the egg and the surface on which it spins.

  19. Current-induced spin-orbit torques in ferromagnetic and antiferromagnetic systems

    KAUST Repository

    Manchon, Aurelien

    2018-01-29

    Spin-orbit coupling in inversion-asymmetric magnetic crystals and structures has emerged as a powerful tool to generate complex magnetic textures, interconvert charge and spin under applied current, and control magnetization dynamics. Current-induced spin-orbit torques mediate the transfer of angular momentum from the lattice to the spin system, leading to sustained magnetic oscillations or switching of ferromagnetic as well as antiferromagnetic structures. The manipulation of magnetic order, domain walls and skyrmions by spin-orbit torques provides evidence of the microscopic interactions between charge and spin in a variety of materials and opens novel strategies to design spintronic devices with potentially high impact in data storage, nonvolatile logic, and magnonic applications. This paper reviews recent progress in the field of spin-orbitronics, focusing on theoretical models, material properties, and experimental results obtained on bulk noncentrosymmetric conductors and multilayer heterostructures, including metals, semiconductors, and topological insulator systems. Relevant aspects for improving the understanding and optimizing the efficiency of nonequilibrium spin-orbit phenomena in future nanoscale devices are also discussed.

  20. Spin-Caloritronic Batteries

    DEFF Research Database (Denmark)

    Yu, Xiao-Qin; Zhu, Zhen-Gang; Su, Gang

    2017-01-01

    The thermoelectric performance of a topological energy converter is analyzed. The H-shaped device is based on a combination of transverse topological effects involving the spin: the inverse spin Hall effect and the spin Nernst effect. The device can convert a temperature drop in one arm into an e...

  1. Frozen spin targets

    CERN Document Server

    Parsons, A S L

    1976-01-01

    Describes six projects which use the frozen-spin principle: Helium-3 R.M.S. and longitudinally polarized frozen spin targets at Rutherford Laboratory, and the frozen spin targets at KEK, Saclay and the one used by the CERN-Helsinki collaboration. (7 refs).

  2. Concepts in spin electronics

    CERN Document Server

    2006-01-01

    A new branch of physics and nanotechnology called spin electronics has emerged, which aims at simultaneously exploiting the charge and spin of electrons in the same device. The aim of this book is to present new directions in the development of spin electronics in both the basic physics and the future electronics.

  3. Spinning Eggs and Ballerinas

    Science.gov (United States)

    Cross, Rod

    2013-01-01

    Measurements are presented on the rise of a spinning egg. It was found that the spin, the angular momentum and the kinetic energy all decrease as the egg rises, unlike the case of a ballerina who can increase her spin and kinetic energy by reducing her moment of inertia. The observed effects can be explained, in part, in terms of rolling friction…

  4. Organic heterostructures based on arylenevinylene oligomers deposited by MAPLE

    Science.gov (United States)

    Socol, M.; Preda, N.; Vacareanu, L.; Grigoras, M.; Socol, G.; Mihailescu, I. N.; Stanculescu, F.; Jelinek, M.; Stanculescu, A.; Stoicanescu, M.

    2014-05-01

    Organic heterostructures were fabricated by matrix assisted pulsed laser evaporation (MAPLE) method using arylenevinylene oligomers based on triphenylamine (P78)/carbazole (P13) group and tris(8-hydroxyquinolinato)aluminum salt (Alq3). Optical properties of the organic multilayer structures were characterized by spectroscopic techniques: FTIR, UV-vis and photoluminescence (PL). A good transparency (over 60%) was remarked for the structures with two organic layers in the 550-800 nm range. Photoluminescence (PL) spectra proved that the emission characteristics of the materials have been preserved. I-V characteristics of (ITO/oligomer/Alq3/Al and ITO/Alq3/Al) heterostructures were symmetrically while rectifying properties of these heterostructures have not been observed. A comparison between the heterostructures made of layers with different thickness reveals that the higher current (8 × 10-6 A at 1 V) was obtained for the ITO/P78/Alq3/Al heterostructure, which is characterized by a larger thickness of the double organic layer. AFM measurements revealed a similar topography while RMS values of the reported structures depend on the organic material.

  5. Magneto-transport study of top- and back-gated LaAlO3/SrTiO3 heterostructures

    Directory of Open Access Journals (Sweden)

    W. Liu

    2015-06-01

    Full Text Available We report a detailed analysis of magneto-transport properties of top- and back-gated LaAlO3/SrTiO3 heterostructures. Efficient modulation in magneto-resistance, carrier density, and mobility of the two-dimensional electron liquid present at the interface is achieved by sweeping top and back gate voltages. Analyzing those changes with respect to the carrier density tuning, we observe that the back gate strongly modifies the electron mobility while the top gate mainly varies the carrier density. The evolution of the spin-orbit interaction is also followed as a function of top and back gating.

  6. One-dimensional hole gas in germanium/silicon nanowire heterostructures

    Science.gov (United States)

    Lu, Wei; Xiang, Jie; Timko, Brian P.; Wu, Yue; Lieber, Charles M.

    2005-07-01

    Two-dimensional electron and hole gas systems, enabled through band structure design and epitaxial growth on planar substrates, have served as key platforms for fundamental condensed matter research and high-performance devices. The analogous development of one-dimensional (1D) electron or hole gas systems through controlled growth on 1D nanostructure substrates, which could open up opportunities beyond existing carbon nanotube and nanowire systems, has not been realized. Here, we report the synthesis and transport studies of a 1D hole gas system based on a free-standing germanium/silicon (Ge/Si) core/shell nanowire heterostructure. Room temperature electrical transport measurements clearly show hole accumulation in undoped Ge/Si nanowire heterostructures, in contrast to control experiments on single-component nanowires. Low-temperature studies show well-controlled Coulomb blockade oscillations when the Si shell serves as a tunnel barrier to the hole gas in the Ge channel. Transparent contacts to the hole gas also have been reproducibly achieved by thermal annealing. In such devices, we observe conductance quantization at low temperatures, corresponding to ballistic transport through 1D subbands, where the measured subband energy spacings agree with calculations for a cylindrical confinement potential. In addition, we observe a “0.7 structure,” which has been attributed to spontaneous spin polarization, suggesting the universality of this phenomenon in interacting 1D systems. Lastly, the conductance exhibits little temperature dependence, consistent with our calculation of reduced backscattering in this 1D system, and suggests that transport is ballistic even at room temperature. Author contributions: W.L., J.X., and C.M.L. designed research; W.L. and J.X. performed research; B.P.T. and Y.W. contributed new reagents/analytic tools; W.L., J.X., and C.M.L. analyzed data; W.L., J.X., and C.M.L. wrote the paper; and B.P.T. and Y.W. developed growth of nanowire

  7. Superior unipolar resistive switching in stacked ZrOx/ZrO2/ZrOx structure

    Directory of Open Access Journals (Sweden)

    Cheng-Li Lin

    2016-03-01

    Full Text Available This study investigates the performance of unipolar-switched ZrO2 RRAM, using an oxygen-deficient and amorphous ZrOx capping in a sandwich stack Al/ZrOx/ZrO2/ZrOx/Al structure. Superior high and low resistance switching and a resistance ratio (HRS/LRS greater than 10 showed excellent dc endurance of 7378 switching cycles and 3.8 × 104 cycles in pulse switching measurements. Recovery behavior, observed in the I-V curve for the SET process (or HRS, led to HRS fluctuations and instability. A new resistance switching model for the stacked ZrO2 RRAM is proposed in this paper. In this model, oxygen-deficient and amorphous ZrOx film, capped on polycrystalline ZrO2 film, plays a key role and acts as an oxygen reservoir in making the oxygen ions redox easily for the SET process and in facilitating re-oxidation for the RESET process, resulting in excellent endurance. By improving the stability and recovery phenomena, engineering parameters of the current control may play a critical role during switching, and they can be correlated to the film’s thickness and the oxygen content of the amorphous ZrOx film.

  8. Estimating verbal intelligence in unipolar depression: comparison of word definition and word recognition.

    Science.gov (United States)

    Suslow, Thomas

    2009-01-01

    Depression is known to be associated with deficits in effortful processing and word fluency. Automatic processes, instead, appear largely intact in depressed patients. It was investigated whether active word definition could be a less appropriate method than passive word recognition as a measure of verbal intelligence in depression. The valid assessment of premorbid IQ is important for correct comparison with current cognitive efficiency of depressed individuals, since premorbid IQ serves as baseline or control parameter to estimate the extent and severity of acquired cognitive impairments, both in the clinical and the research context. Two vocabulary tests were administered to 90 patients (31 women) with unipolar depression and 30 control subjects (15 women): a word definition task [the vocabulary subtest of the Wechsler Adult Intelligence Scale (WAIS-R)] and a word recognition task [the Multiple choice vocabulary test (MWT)]. In the depressed sample, scores of the MWT tended to be higher than WAIS-R scores. For depressed women, the MWT score was significantly higher than the WAIS-R score. In the control sample, no differences between MWT and WAIS-R scores were observed. Our findings indicate that word definition tasks could underestimate verbal intelligence especially in depressed women. For depressed women, it could be more appropriate to administer word recognition than word definition as an estimate of premorbid or verbal intelligence.

  9. Distinguishing bipolar II depression from unipolar major depressive disorder: Differences in heart rate variability.

    Science.gov (United States)

    Chang, Hsin-An; Chang, Chuan-Chia; Kuo, Terry B J; Huang, San-Yuan

    2015-01-01

    Bipolar II (BPII) depression is commonly misdiagnosed as unipolar depression (UD); however, an objective and reliable tool to differentiate between these disorders is lacking. Whether cardiac autonomic function can be used as a biomarker to distinguish BPII from UD is unknown. We recruited 116 and 591 physically healthy patients with BPII depression and UD, respectively, and 421 healthy volunteers aged 20-65 years. Interviewer and self-reported measures of depression/anxiety severity were obtained. Cardiac autonomic function was evaluated by heart rate variability (HRV) and frequency-domain indices of HRV. Patients with BPII depression exhibited significantly lower mean R-R intervals, variance (total HRV), low frequency (LF)-HRV, and high frequency (HF)-HRV but higher LF/HF ratio compared to those with UD. The significant differences remained after adjusting for age. Compared to the controls, the patients with BPII depression showed cardiac sympathetic excitation with reciprocal vagal impairment, whereas the UD patients showed only vagal impairment. Depression severity independently contributed to decreased HRV and vagal tone in both the patients with BPII depression and UD, but increased sympathetic tone only in those with BPII depression. HRV may aid in the differential diagnosis of BPII depression and UD as an adjunct to diagnostic interviews.

  10. Cognition-related brain networks underpin the symptoms of unipolar depression: Evidence from a systematic review.

    Science.gov (United States)

    Rayner, Genevieve; Jackson, Graeme; Wilson, Sarah

    2016-02-01

    This systematic review sources the latest neuroimaging evidence for the role of cognition-related brain networks in depression, and relates their abnormal functioning to symptoms of the disorder. Using theoretically informed and rigorous inclusion criteria, we integrate findings from 59 functional neuroimaging studies of adults with unipolar depression using a narrative approach. Results demonstrate that two distinct neurocognitive networks, the autobiographic memory network (AMN) and the cognitive control network (CCN), are central to the symptomatology of depression. Specifically, hyperactivity of the introspective AMN is linked to pathological brooding, self-blame, rumination. Anticorrelated under-engagement of the CCN is associated with indecisiveness, negative automatic thoughts, poor concentration, distorted cognitive processing. Downstream effects of this imbalance include reduced regulation of networks linked to the vegetative and affective symptoms of depression. The configurations of these networks can change between individuals and over time, plausibly accounting for both the variable presentation of depressive disorders and their fluctuating course. Framing depression as a disorder of neurocognitive networks directly links neurobiology to psychiatric practice, aiding researchers and clinicians alike. Copyright © 2015 Elsevier Ltd. All rights reserved.

  11. Season of birth, clinical manifestations and Dexamethasone Suppression Test in unipolar major depression

    Directory of Open Access Journals (Sweden)

    Kaprinis George S

    2007-08-01

    Full Text Available Abstract Background Reports in the literature suggest that the season of birth might constitute a risk factor for the development of a major psychiatric disorder, possibly because of the effect environmental factors have during the second trimester of gestation. The aim of the current paper was to study the possible relationship of the season of birth and current clinical symptoms in unipolar major depression. Methods The study sample included 45 DSM-IV major depressive patients and 90 matched controls. The SCAN v. 2.0, Hamilton Depression Rating Scale (HDRS and Hamilton Anxiety Scale (HAS were used to assess symptomatology, and the 1 mg Dexamethasone Suppression Test (DST was used to subcategorize patients. Results Depressed patients as a whole did not show differences in birth season from controls. However, those patients born during the spring manifested higher HDRS while those born during the summer manifested the lowest HAS scores. DST non-suppressors were almost exclusively (90% likely to be born during autumn and winter. No effect from the season of birth was found concerning the current severity of suicidal ideation or attempts. Discussion The current study is the first in this area of research using modern and rigid diagnostic methodology and a biological marker (DST to categorize patients. Its disadvantages are the lack of data concerning DST in controls and a relatively small size of patient sample. The results confirm the effect of seasonality of birth on patients suffering from specific types of depression.

  12. Mental imagery in bipolar affective disorder versus unipolar depression: investigating cognitions at times of 'positive' mood.

    Science.gov (United States)

    Ivins, Annabel; Di Simplicio, Martina; Close, Helen; Goodwin, Guy M; Holmes, Emily

    2014-09-01

    Compared to unipolar depression (UD), depressed mood in bipolar disorder (BD) has been associated with amplified negative mental imagery of the future ('flashforwards'). However, imagery characteristics during positive mood remain poorly explored. We hypothesise first, that unlike UD patients, the most significant positive images of BD patients will be 'flashforwards' (rather than past memories). Second, that BD patients will experience more frequent (and more 'powerful') positive imagery as compared to verbal thoughts and third, that behavioural activation scores will be predicted by imagery variables in the BD group. BD (n=26) and UD (n=26) patients completed clinical and trait imagery measures followed by an Imagery Interview and a measure of behavioural activation. Compared to UD, BD patients reported more 'flashforwards' compared to past memories and rated their 'flashforwards' as more vivid, exciting and pleasurable. Only the BD group found positive imagery more 'powerful', (preoccupying, 'real' and compelling) as compared to verbal thoughts. Imagery-associated pleasure predicted levels of drive and reward responsiveness in the BD group. A limitation in the study was the retrospective design. Moreover pathological and non-pathological periods of "positive" mood were not distinguished in the BD sample. This study reveals BD patients experience positive 'flashforward' imagery in positive mood, with more intense qualities than UD patients. This could contribute to the amplification of emotional states and goal directed behaviour leading into mania, and differentiate BD from UD. Copyright © 2014 The Authors. Published by Elsevier B.V. All rights reserved.

  13. Effects of quetiapine on sleep architecture in patients with unipolar or bipolar depression.

    Science.gov (United States)

    Gedge, Laura; Lazowski, Lauren; Murray, David; Jokic, Ruzica; Milev, Roumen

    2010-09-07

    To determine the effect of adjunctive quetiapine therapy on the sleep architecture of patients with bipolar or unipolar depression. This is a prospective, single-blind, repeated measures polysomnographic study. Sleep architecture was analyzed by overnight polysomnography, and subjective sleep quality was measured using the Pittsburgh Sleep Quality Index. The Hamilton Rating Scale for Depression, Montgomery Asberg Depression Rating Scale, Young Mania Rating Scale, and Clinical Global Impression-Severity Scale were employed to quantify changes in illness severity with adjunctive quetiapine treatment. Polysomnographs and clinical measures were administered at baseline, after 2-4 days of treatment, and after 21-28 days of quetiapine treatment. The average dose of quetiapine was 155 mg, ranging from 100-200 mg. Adjunctive quetiapine therapy did not significantly alter sleep efficiency, sleep continuity, or Pittsburgh Sleep Quality Index scores. Respiratory Disturbance Index and percentage of total time in rapid eye movement (REM) sleep significantly decreased and the percentage of total time in non-REM sleep, and duration of Stage 2 and non-REM sleep significantly increased after 2-4 days of quetiapine treatment. Illness severity significantly decreased over time. Adjunctive quetiapine treatment alters sleep architecture in patients with major depressive disorder or bipolar disorder, which may partially explain its early antidepressant properties. Changes in sleep architecture are more robust and significant within two to four days of starting treatment.

  14. Long-term odor recognition memory in unipolar major depression and Alzheimer׳s disease.

    Science.gov (United States)

    Naudin, Marine; Mondon, Karl; El-Hage, Wissam; Desmidt, Thomas; Jaafari, Nematollah; Belzung, Catherine; Gaillard, Philippe; Hommet, Caroline; Atanasova, Boriana

    2014-12-30

    Major depression and Alzheimer׳s disease (AD) are often observed in the elderly. The identification of specific markers for these diseases could improve their screening. The aim of this study was to investigate long-term odor recognition memory in depressed and AD patients, with a view to identifying olfactory markers of these diseases. We included 20 patients with unipolar major depressive episodes (MDE), 20 patients with mild to moderate AD and 24 healthy subjects. We investigated the cognitive profile and olfactory memory capacities (ability to recognize familiar and unfamiliar odors) of these subjects. Olfactory memory test results showed that AD and depressed patients were characterized by significantly less correct responses and more wrong responses than healthy controls. Detection index did not differ significantly between patients with major depression and those with AD when the results were analyzed for all odors. However, MDE patients displayed an impairment of olfactory memory for both familiar and unfamiliar odors, whereas AD subjects were impaired only in the recognition of unfamiliar odors, with respect to healthy subjects. If preservation of olfactory memory for familiar stimuli in patients with mild to moderate AD is confirmed, this test could be used in clinical practice as a complementary tool for diagnosis. Copyright © 2014 Elsevier Ireland Ltd. All rights reserved.

  15. Severe Intellectual Disability: Systematic Review of the Prevalence and Nature of Presentation of Unipolar Depression.

    Science.gov (United States)

    Walton, Catherine; Kerr, Mike

    2016-09-01

    The diagnosis of depression in severe and profound intellectual disability is challenging. Without adequate skills in verbal self-expression, standardized diagnostic criteria cannot be used with confidence. The purpose of this systematic review was to investigate the assessment and diagnosis of unipolar depression in severe and profound intellectual disability. The review aimed to examine the methods used to assess for depression. The secondary aim was to explore the frequency and symptoms of depression. The PRISMA (2009) Checklist for systematic review was followed, and a search of electronic databases was undertaken. Nine studies were included in the qualitative synthesis from over 2000 records identified. The quality of the studies was assessed and scored, with a wide range of results. Individual studies scored between 2 and 7 of a maximum possible score of 8. The diagnostic tools utilized by each of the studies were assessed and compared. In terms of the methods used to assess for depression, results were varied. This was due to the heterogeneous nature of the individual study designs. The Aberrant Behaviour Checklist consistently showed promise, in particular when combined with other instruments or clinical examination. Qualitative analysis of the selected studies has shown a wide variation in the quality of primary research in this field, with more required to make firm conclusions regarding the diagnosis, frequency and presentation of depression in severe and profound intellectual disability. © 2015 John Wiley & Sons Ltd.

  16. Crystalline Kitaev spin liquids

    Science.gov (United States)

    Yamada, Masahiko G.; Dwivedi, Vatsal; Hermanns, Maria

    2017-10-01

    Frustrated magnetic systems exhibit many fascinating phases. Prime among them are quantum spin liquids, where the magnetic moments do not order even at zero temperature. A subclass of quantum spin liquids called Kitaev spin liquids are particularly interesting, because they are exactly solvable, can be realized in certain materials, and show a large variety of gapless and gapped phases. Here we show that nonsymmorphic symmetries can enrich spin liquid phases, such that the low-energy spinon degrees of freedom form three-dimensional Dirac cones or nodal chains. In addition, we suggest a realization of such Kitaev spin liquids in metal-organic frameworks.

  17. Spin physics in semiconductors

    CERN Document Server

    2017-01-01

    This book offers an extensive introduction to the extremely rich and intriguing field of spin-related phenomena in semiconductors. In this second edition, all chapters have been updated to include the latest experimental and theoretical research. Furthermore, it covers the entire field: bulk semiconductors, two-dimensional semiconductor structures, quantum dots, optical and electric effects, spin-related effects, electron-nuclei spin interactions, Spin Hall effect, spin torques, etc. Thanks to its self-contained style, the book is ideally suited for graduate students and researchers new to the field.

  18. Graphene/Si-nanowire heterostructure molecular sensors.

    Science.gov (United States)

    Kim, Jungkil; Oh, Si Duk; Kim, Ju Hwan; Shin, Dong Hee; Kim, Sung; Choi, Suk-Ho

    2014-06-20

    Wafer-scale graphene/Si-nanowire (Si-NW) array heterostructures for molecular sensing have been fabricated by vertically contacting single-layer graphene with high-density Si NWs. Graphene is grown in large scale by chemical vapour deposition and Si NWs are vertically aligned by metal-assisted chemical etching of Si wafer. Graphene plays a key role in preventing tips of vertical Si NWs from being bundled, thereby making Si NWs stand on Si wafer separately from each other under graphene, a critical structural feature for the uniform Schottky-type junction between Si NWs and graphene. The molecular sensors respond very sensitively to gas molecules by showing 37 and 1280% resistance changes within 3.5/0.15 and 12/0.15 s response/recovery times under O2 and H2 exposures in air, respectively, highest performances ever reported. These results together with the sensor responses in vacuum are discussed based on the surface-transfer doping mechanism.

  19. Proximity coupling in superconductor-graphene heterostructures.

    Science.gov (United States)

    Lee, Gil-Ho; Lee, Hu-Jong

    2018-02-16

    This review discusses the electronic properties and the prospective research directions of superconductor-graphene heterostructures. The basic electronic properties of graphene are introduced to highlight the unique possibility of combining two seemingly unrelated physics, superconductivity and relativity. We then focus on graphene-based Josephson junctions, one of the most versatile superconducting quantum devices. The various theoretical methods that have been developed to describe graphene Josephson junctions are examined, together with their advantages and limitations, followed by a discussion on the advances in device fabrication and the relevant length scales. The phase-sensitive properties and phase-particle dynamics of graphene Josephson junctions are examined to provide an understanding of the underlying mechanisms of Josephson coupling via graphene. Thereafter, microscopic transport of correlated quasiparticles produced by Andreev reflections at superconducting interfaces and their phase-coherent behaviors are discussed. Quantum phase transitions studied with graphene as an electrostatically tunable two-dimensional platform are reviewed. The interplay between proximity-induced superconductivity and the quantum-Hall phase is discussed as a possible route to study topological superconductivity and non-Abelian physics. Finally, a brief summary on the prospective future research directions is given. © 2018 IOP Publishing Ltd.

  20. Levels of triglycerides, cholesterol, LDL, HDL and glucose in patients with schizophrenia, unipolar depression and bipolar disorder.

    Science.gov (United States)

    Wysokiński, Adam; Strzelecki, Dominik; Kłoszewska, Iwona

    2015-01-01

    The aim of this study is to investigate differences in triglycerides (TGA), cholesterol (TC), HDL, LDL and glucose (FPG) levels in patients with acute schizophrenia, unipolar depression, bipolar depression and bipolar mania. Results for 2305 Caucasian patients were included in the study (1377 women, 59.7%; mean age 45.6). Mean TGA level was: schizophrenia: 139.9±90.6 mg/dL, unipolar depression: 125.4±70.8 mg/dL, bipolar disorder: 141.1±81.9 mg/dL, bipolar depression: 147.7±82.8 mg/dL mg/dL, bipolar mania: 120.2±76.1 mg/dL, inter-group differences were significant (pschizophrenia: 188.5±40.4 mg/dL, unipolar depression: 198.8±50.7 mg/dL, bipolar disorder: 194.4±48.3 mg/dL, bipolar depression: 198.9±48.8 mg/dL, bipolar mania: 180.1±43.8 mg/dL, inter-group differences were significant (pschizophrenia: 45.3±13.9 mg/dL, unipolar depression: 48.1±14.8 mg/dL, bipolar disorder: 45.4±15.3 mg/dL, bipolar depression: 45.1±15.4 mg/dL, bipolar mania: 46.4±15.1 mg/dL, inter-group differences were significant (pschizophrenia: 115.4±34.7 mg/dL, unipolar depression: 125.7±44.1 mg/dL, bipolar disorder: 120.9±42.1 mg/dL, bipolar depression: 124.5±43.1 mg/dL, bipolar mania: 109.3±36.9 mg/dL, inter-group differences were significant (pschizophrenia: 95.9±24.9 mg/dL, unipolar depression: 94.8±22.9 mg/dL, bipolar disorder: 97.2±24.4 mg/dL, bipolar depression: 98.3±25.3 mg/dL, bipolar mania: 93.9±21.1 mg/dL, inter-group differences were not significant (p=0.08). Odds ratios for glucose and lipids abnormalities, correlations with age, sex distribution in diagnostic groups for normal ranges of glucose and lipids, differences in glucose and lipids levels between the age groups were also calculated. Our results confirm that there is a high prevalence of lipid and glucose abnormalities in patients with schizophrenia and mood disorders (both unipolar and bipolar). However, we have demonstrated that these diagnostic groups differ in terms of types and frequency of these

  1. Highly Confined Electronic and Ionic Conduction in Oxide Heterostructures

    DEFF Research Database (Denmark)

    Pryds, Nini

    2015-01-01

    The conductance confined at the interface of complex oxide heterostructures provides new opportunities to explore nanoelectronic as well as nanoionic devices. In this talk I will present our recent results both on ionic and electronic conductivity at different heterostructures systems. In the first...... unattainable for Bi2O3-based materials, is achieved[1]. These confined heterostructures provide a playground not only for new high ionic conductivity phenomena that are sufficiently stable but also uncover a large variety of possible technological perspectives. At the second part, I will discuss and show our...... recent results of high mobile samples realized by, interface confined redox reactions[2], strain induced polarization[3]and modulation doping at complex oxide interfaces. This collection of samples offers unique opportunities for a wide range of rich world of mesoscopic physics. [1] S. Sanne et al...

  2. Epitaxial growth and physical properties of Heusler/perovskite heterostructures

    Science.gov (United States)

    Kobayashi, K.; Ueda, K.; Fukatani, N.; Kawada, H.; Sakuma, K.; Asano, H.

    2013-08-01

    Multiferroic heterostructures of the ferromagnetic, half-metallic Heusler Fe2CrSi (FCS) and the ferroelectric perovskite Ba0.7Sr0.3TiO3 (BSTO) have been formed by magnetron sputtering, and their magnetic and ferroelectric properties have been investigated. FCS/BSTO bilayer structures were epitaxially grown on LaAlO3 substrates with epitaxial relationships of FCS (001)[110]//BSTO (001)[100]. Multiferroic properties with a remanent polarization of 10.6 µC/cm2 and a saturation magnetization of 417 emu/cc were observed for the FCS/BSTO heterostructures at room temperature. These results suggest that the Heusler/perovskite epitaxial heterostructure is a promising candidate for fabricating multiferroic devices.

  3. Electronic homogeneity of nanowire heterostructure Light Emitting Diodes (LEDs)

    Science.gov (United States)

    Selcu, Camelia; May, Brelon J.; Sarwar, A. T. M. Golam; Myers, Roberto C.

    In addition to low defect densities and great tunability bandgap within a single heterostructure, the possibility of growing (Al, In,_) GaN nanowire heterostructure LEDs on different substrates while maintaining their high electronic and optical properties makes them very attractive. We investigated the electronic homogeneity of the (Al, In,_) GaN nanowire ensemble by acquiring current maps at certain applied biases using conductive AFM. By taken IVs on individual nanowires, we found that different wires have different turn on voltages and that some of the nanowires degrade due to the applied bias.

  4. Exfoliation and van der Waals heterostructure assembly of intercalated ferromagnet Cr1/3TaS2

    Science.gov (United States)

    Yamasaki, Yuji; Moriya, Rai; Arai, Miho; Masubuchi, Satoru; Pyon, Sunseng; Tamegai, Tsuyoshi; Ueno, Keiji; Machida, Tomoki

    2017-12-01

    Ferromagnetic van der Waals (vdW) materials are in demand for spintronic devices with all-two-dimensional-materials heterostructures. Here, we demonstrate mechanical exfoliation of magnetic-atom-intercalated transition metal dichalcogenide Cr1/3TaS2 from its bulk crystal; previously such intercalated materials were thought difficult to exfoliate. Magnetotransport in exfoliated tens-of-nanometres-thick flakes revealed ferromagnetic ordering below its Curie temperature T C ~ 110 K as well as strong in-plane magnetic anisotropy; these are identical to its bulk properties. Further, van der Waals heterostructure assembly of Cr1/3TaS2 with another intercalated ferromagnet Fe1/4TaS2 is demonstrated using a dry-transfer method. The fabricated heterojunction composed of Cr1/3TaS2 and Fe1/4TaS2 with a native Ta2O5 oxide tunnel barrier in between exhibits tunnel magnetoresistance (TMR), revealing possible spin injection and detection with these exfoliatable ferromagnetic materials through the vdW junction.

  5. Transforming common III-V/II-VI insulating building blocks into topological heterostructure via the intrinsic electric polarization

    Science.gov (United States)

    Zunger, Alex; Zhang, Xiuwen; Abdalla, Leonardo; Liu, Qihang

    Currently known topological insulators (TIs) are limited to narrow gap compounds incorporating heavy elements, thus severely limiting the material pool available for such applications. We show how a heterovalent superlattice made of common semiconductor building blocks can transform its non-TI components into a topological heterostructure. The heterovalent nature of such interfaces sets up, in the absence of interfacial atomic exchange, a natural internal electric field that along with the quantum confinement leads to band inversion, transforming these semiconductors into a topological phase while also forming a giant Rashba spin splitting. We demonstrate this paradigm of designing TIs from ordinary semiconductors via first-principle calculations on III-V/II-VI superlattice InSb/CdTe. We illustrate the relationship between the interfacial stability and the topological transition, finding a ``window of opportunity'' where both conditions can be optimized. This work illustrates the general principles of co-evaluation of TI functionality with thermodynamic stability as a route of identifying realistic combination of common insulators that could produce topological heterostructures. This work was supported by Basic Energy Science, MSE division (Grant DE-FG02-13ER46959).

  6. Voltage-controlled ferromagnetism and magnetoresistance in LaCoO{sub 3}/SrTiO{sub 3} heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Hu, Chengqing; Park, Keun Woo; Yu, Edward T. [Microelectronics Research Center, The University of Texas at Austin, 10100 Burnet Rd., Austin, Texas 78758 (United States); Posadas, Agham; Demkov, Alexander A. [Department of Physics, The University of Texas at Austin, 1 University Station C1600, Austin, Texas 78712 (United States); Jordan-Sweet, Jean L. [IBM Thomas J. Watson Research Center, Yorktown Heights, New York 10598 (United States)

    2013-11-14

    A LaCoO{sub 3}/SrTiO{sub 3} heterostructure grown on Si (001) is shown to provide electrically switchable ferromagnetism, a large, electrically tunable magnetoresistance, and a vehicle for achieving and probing electrical control over ferromagnetic behavior at submicron dimensions. Fabrication of devices in a field-effect transistor geometry enables application of a gate bias voltage that modulates strain in the heterostructure via the converse piezoelectric effect in SrTiO{sub 3}, leading to an artificial inverse magnetoelectric effect arising from the dependence of ferromagnetism in the LaCoO{sub 3} layer on strain. Below the Curie temperature of the LaCoO{sub 3} layer, this effect leads to modulation of resistance in LaCoO{sub 3} as large as 100%, and magnetoresistance as high as 80%, both of which arise from carrier scattering at ferromagnetic-nonmagnetic interfaces in LaCoO{sub 3}. Finite-element numerical modeling of electric field distributions is used to explain the dependence of carrier transport behavior on gate contact geometry, and a Valet-Fert transport model enables determination of spin polarization in the LaCoO{sub 3} layer. Piezoresponse force microscopy is used to confirm the existence of piezoelectric response in SrTiO{sub 3} grown on Si (001). It is also shown that this structure offers the possibility of achieving exclusive-NOR logic functionality within a single device.

  7. Anisotropic Pauli Spin Blockade of Holes in a GaAs Double Quantum Dot

    Science.gov (United States)

    Wang, Qingwen; Klochan, Oleh; Hung, Jo-Tzu; Culcer, Dimitrie; Farrer, Ian; Ritchie, David; Hamilton, Alex

    Electrically defined semiconductor quantum dots are appealing systems for spin manipulation and quantum information processing. Thanks to the weak hyperfine interaction and the strong spin-orbit interaction, heavy-holes in GaAs are promising candidates for all-electrical spin manipulation. However, making stable quantum dots in GaAs has only become possible recently, mainly because of difficulties in device fabrication and device stability. Here we present electrical transport measurements of heavy-holes in a lateral double quantum dot based on a GaAs /AlxGa1 - x As heterostructure. We observe clear Pauli spin blockade and show that the lifting of the spin blockade by an external magnetic field is extremely anisotropic. Numerical calculations of heavy-hole transport through a double quantum dot in the presence of strong spin-orbit interaction demonstrate quantitative agreement with experimental results, which indicates that the observed anisotropy can be explained by the anisotropic hole g-factor and the surface Dresselhaus spin-orbit coupling.

  8. Dissociative symptoms reflect levels of tumor necrosis factor alpha in patients with unipolar depression

    Directory of Open Access Journals (Sweden)

    Bizik G

    2014-04-01

    Full Text Available Gustav Bizik,1 Petr Bob,1 Jiri Raboch,1 Josef Pavlat,1 Jana Uhrova,2 Hana Benakova,2 Tomas Zima2 1Center for Neuropsychiatric Research of Traumatic Stress, Department of Psychiatry and UHSL, 2Department of Clinical Biochemistry and Laboratory Diagnostics, 1st Faculty of Medicine, Charles University, Prague, Czech Republic Abstract: Recent evidence indicates that the nature of interactions between the nervous system and immune system is important in the pathogenesis of depression. Specifically, alterations in pro-inflammatory cytokines have been related to the development of several psychological and neurobiological manifestations of depressive disorder, as well as to stress exposure. A number of findings point to tumor necrosis factor alpha (TNF-α as one of the central factors in these processes. Accordingly, in the present study, we test the hypothesis that specific influences of chronic stressors related to traumatic stress and dissociation are related to alterations in TNF-α levels. We performed psychometric measurement of depression (Beck Depression Inventory [BDI]-II, traumatic stress symptoms (Trauma Symptom Checklist [TSC]-40, and psychological and somatoform dissociation (Dissociative Experiences Scale [DES] and Somatoform Dissociation Questionnaire [SDQ]-20, respectively, and immunochemical measure of serum TNF-α in 66 inpatients with unipolar depression (mean age 43.1 ± 7.3 years. The results show that TNF-α is significantly related to DES (Spearman R=−0.42, P<0.01, SDQ-20 (Spearman R=−0.38, P<0.01, and TSC-40 (Spearman R=−0.41, P<0.01, but not to BDI-II. Results of the present study suggest that TNF-α levels are related to dissociative symptoms and stress exposure in depressed patients. Keywords: depression, dissociation, TNF-alpha, traumatic stress

  9. Personalized cognitive training in unipolar and bipolar disorder: a study of cognitive functioning

    Directory of Open Access Journals (Sweden)

    Marek ePreiss

    2013-05-01

    Full Text Available Patients with unipolar depressive disorder and in the depressive phase of bipolar disorder often manifest psychological distress and cognitive deficits, notably in Executive Control. We used computerized cognitive training in anattempt to reduce psychological affliction, improve everyday coping and cognitive function. We asked one group of patients (intervention group to engage in cognitive training three times a week, for 20 minutes each time, for eight consecutive weeks. A second group of patients (control group received standard care only. Before the onset of training we administered to all patients self-report questionnaires of mood, mental and psychological health, and everyday coping. We also assessed Executive Control using a broad computerized neurocognitive battery of tests which yielded, among others, scores in Working Memory, Shifting, Inhibition, Visuomotor Vigilance, Divided Attention, Memory Span and a Global Executive Function score. All questionnaires and tests were re-administered to the patients who adhered to the study at the end of training. When we compared the groups (between-group comparisons on the amount of change that had taken place from baseline to post-training, we found improvements in Executive Control. Further exploration of the data showed that the cognitive improvements did not predict the improvements in everyday coping, and mood. Single-group data (within-group comparisons show that patients in the intervention group were reporting fewer cognitive failures, fewer dysexecutive incidents and less difficulty in everyday coping. This group had also improved significantly on the six Executive Control tests and on the Global Executive Control score. By contrast, the control group improved only on the reports of cognitive failure and on working memory.

  10. Effects of quetiapine on sleep architecture in patients with unipolar or bipolar depression

    Directory of Open Access Journals (Sweden)

    Laura Gedge

    2010-08-01

    Full Text Available Laura Gedge1, Lauren Lazowski1, David Murray2, Ruzica Jokic2,3, Roumen Milev2,31Centre for Neuroscience Studies, 2Department of Psychiatry, Queen’s University, Kingston, 3Providence Care-Mental Health Services, Kingston, Ontario, CanadaObjective: To determine the effect of adjunctive quetiapine therapy on the sleep architecture of patients with bipolar or unipolar depression.Methods: This is a prospective, single-blind, repeated measures polysomnographic study. Sleep architecture was analyzed by overnight polysomnography, and subjective sleep quality was measured using the Pittsburgh Sleep Quality Index. The Hamilton Rating Scale for Depression, Montgomery Asberg Depression Rating Scale, Young Mania Rating Scale, and Clinical Global Impression-Severity Scale were employed to quantify changes in illness severity with adjunctive quetiapine treatment. Polysomnographs and clinical measures were administered at baseline, after 2–4 days of treatment, and after 21–28 days of quetiapine treatment. The average dose of quetiapine was 155 mg, ranging from 100–200 mg.Results: Adjunctive quetiapine therapy did not significantly alter sleep efficiency, sleep continuity, or Pittsburgh Sleep Quality Index scores. Respiratory Disturbance Index and percentage of total time in rapid eye movement (REM sleep significantly decreased and the percentage of total time in non-REM sleep, and duration of Stage 2 and non-REM sleep significantly increased after 2–4 days of quetiapine treatment. Illness severity significantly decreased over time.Conclusions: Adjunctive quetiapine treatment alters sleep architecture in patients with major depressive disorder or bipolar disorder, which may partially explain its early antidepressant properties. Changes in sleep architecture are more robust and significant within two to four days of starting treatment.Keywords: quetiapine, sleep architecture, depression, bipolar disorder

  11. Enduring cognitive dysfunction in unipolar major depression: a test-retest study using the Stroop paradigm.

    Science.gov (United States)

    Hammar, Asa; Sørensen, Lin; Ardal, Guro; Oedegaard, Ketil Joachim; Kroken, Rune; Roness, Atle; Lund, Anders

    2010-08-01

    The aim of the study was to investigate automatic and effortful information processing with the Stroop paradigm in a long term perspective in patients with major depressive disorder (MDD). Patients were tested at two test occasions: at inclusion with a Hamilton Depression Rating Scale (HDRS) score >18, and after 6 months, when most patients had experienced symptom reduction. The Stroop paradigm is considered to measure aspects of attention and executive functioning and consists of three conditions/cards: naming the color of the patches (Color), reading of the color-words (Word) and naming the ink color of color-words (Color-Word). The Color-Word condition is proved to be the most cognitive demanding task and requires the proband to actively suppress interference and is therefore considered to require more effortful information processing, whereas naming the color of the patches and reading the color-words are expected to be more automatic and less cognitive demanding. A homogenous group of 19 patients with unipolar recurrent MDD according to DSM-IV and a HDRS score of >18 were included in the study. A control group was individually matched for age, gender and level of education. Depressed patients performed equal to the control group on the Color and Word cards at both test occasions. However, the patients were impaired compared with the control group on the Color-Word card task at both test occasions. Thus, the depressed patients showed no improvement of effortful attention/executive performance as a function of symptom reduction. The results indicate that the depressed patients showed impaired cognitive performance on cognitive demanding tasks when symptomatic and that this impairment prevailed after 6 months, despite significant improvement in their depressive symptoms.

  12. Higher Spin Matrix Models

    Directory of Open Access Journals (Sweden)

    Mauricio Valenzuela

    2017-10-01

    Full Text Available We propose a hybrid class of theories for higher spin gravity and matrix models, i.e., which handle simultaneously higher spin gravity fields and matrix models. The construction is similar to Vasiliev’s higher spin gravity, but part of the equations of motion are provided by the action principle of a matrix model. In particular, we construct a higher spin (gravity matrix model related to type IIB matrix models/string theory that have a well defined classical limit, and which is compatible with higher spin gravity in A d S space. As it has been suggested that higher spin gravity should be related to string theory in a high energy (tensionless regime, and, therefore to M-Theory, we expect that our construction will be useful to explore concrete connections.

  13. Spin caloritronics in graphene

    Energy Technology Data Exchange (ETDEWEB)

    Ghosh, Angsula; Frota, H. O. [Department of Physics, Federal University of Amazonas, Av. Rodrigo Octavio 3000-Japiim, 69077-000 Manaus, AM (Brazil)

    2015-06-14

    Spin caloritronics, the combination of spintronics with thermoelectrics, exploiting both the intrinsic spin of the electron and its associated magnetic moment in addition to its fundamental electronic charge and temperature, is an emerging technology mainly in the development of low-power-consumption technology. In this work, we study the thermoelectric properties of a Rashba dot attached to two single layer/bilayer graphene sheets as leads. The temperature difference on the two graphene leads induces a spin current, which depends on the temperature and chemical potential. We demonstrate that the Rashba dot behaves as a spin filter for selected values of the chemical potential and is able to filter electrons by their spin orientation. The spin thermopower has also been studied where the effects of the chemical potential, temperature, and also the Rashba term have been observed.

  14. Higher spin gauge theories

    CERN Document Server

    Henneaux, Marc; Vasiliev, Mikhail A

    2017-01-01

    Symmetries play a fundamental role in physics. Non-Abelian gauge symmetries are the symmetries behind theories for massless spin-1 particles, while the reparametrization symmetry is behind Einstein's gravity theory for massless spin-2 particles. In supersymmetric theories these particles can be connected also to massless fermionic particles. Does Nature stop at spin-2 or can there also be massless higher spin theories. In the past strong indications have been given that such theories do not exist. However, in recent times ways to evade those constraints have been found and higher spin gauge theories have been constructed. With the advent of the AdS/CFT duality correspondence even stronger indications have been given that higher spin gauge theories play an important role in fundamental physics. All these issues were discussed at an international workshop in Singapore in November 2015 where the leading scientists in the field participated. This volume presents an up-to-date, detailed overview of the theories i...

  15. Agitated "unipolar" depression re-conceptualized as a depressive mixed state: implications for the antidepressant-suicide controversy.

    Science.gov (United States)

    Akiskal, Hagop S; Benazzi, Franco; Perugi, Giulio; Rihmer, Zoltán

    2005-04-01

    The nosologic status of agitated depression is unresolved. Are they unipolar (UP) or bipolar (BP)? Are they mixed states? Even more controversial is the notion that antidepressants might play some role in the suicidality of such patients (Akiskal and Mallya, 1987) [Akiskal, H.S., Mallya, G., 1987. Criteria for the "soft" bipolar spectrum: treatment implications. Psychopharmacol Bull. 23, 68-73]. After excluding all patients with history of hypomanic episodes occurring outside the frame of a major depressive episode (MDE), even those with a shorter duration of hypomanic symptoms than stipulated in DSM-IV, the remaining consecutive 254 unipolar major depressive disorder (MDD) private adult (> 21 years old) outpatients were interviewed (off psychoactive drugs for 2 weeks) with the Structured Clinical Interview for DSM-IV (SCID-CV), the Hypomania Interview Guide (HIGH-C), and the Family History Screen. Intra-MDE hypomanic symptoms were systematically assessed, with > or = 3 such symptoms required for a diagnosis of depressive mixed state (DMX). Agitated depression was defined as an MDE with HIGH-C psychomotor agitation score > or = 2. Logistic regression was used to study associations and control for confounding variables. In this strictly defined unipolar sample, agitated depression was present in 19.7%. Compared with its non-agitated counterpart, it had significantly fewer recurrences, less chronicity, higher rate of family history for bipolar disorder, and DMX; and, among the intra-depressive non-euphoric hypomanic symptoms (in decreasing order of frequency), distractibility, racing/crowded thoughts, irritable mood, talkativeness, and risky behavior. The most striking finding was the robust association between agitated depression and DMX (OR = 36.9). Furthermore, patients with psychomotor agitation had significantly higher rate of weight loss and suicidal ideation. Of DMX symptoms, we found an association between suicidal ideation, psychomotor activation, and racing

  16. Silicon spin communication

    OpenAIRE

    Dery, Hanan; Song, Yang; Li, Pengke; Zutic, Igor

    2011-01-01

    Recent experimental breakthroughs have demonstrated that the electron spin in silicon can be reliably injected and detected as well as transferred over distances exceeding 1 mm. We propose an on-chip communication paradigm which is based on modulating spin polarization of a constant current in silicon wires. We provide figures of merit for this scheme by studying spin relaxation and drift-diffusion models in silicon.

  17. Spin coating apparatus

    Science.gov (United States)

    Torczynski, John R.

    2000-01-01

    A spin coating apparatus requires less cleanroom air flow than prior spin coating apparatus to minimize cleanroom contamination. A shaped exhaust duct from the spin coater maintains process quality while requiring reduced cleanroom air flow. The exhaust duct can decrease in cross section as it extends from the wafer, minimizing eddy formation. The exhaust duct can conform to entrainment streamlines to minimize eddy formation and reduce interprocess contamination at minimal cleanroom air flow rates.

  18. Investigation of the Bir-Aronov-Pikus spin relaxation mechanism in (110) GaAs quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Oertel, Stefan; Huebner, Jens; Oestreich, Michael [Universitaet Hannover (Germany). Institut fuer Festkoerperphysik, Abteilung Nanostrukturen; Schuh, Dieter; Wegscheider, Werner [Universitaet Regensburg (Germany). Institut fuer Experimentelle und Angewandte Physik

    2009-07-01

    We determine the spin relaxation time {tau}{sub s} in (110)-oriented GaAs quantum wells by time- and polarization resolved photoluminescence spectroscopy. The major spin relaxation channel in III-V compounds, the D'yakonov-Perel' mechanism, is suppressed in growth direction of (110)-oriented heterostructures and the most prominent remaining spin relaxation mechanism in these quantum wells is the Bir-Aronov-Pikus (BAP) mechanism via interaction with unpolarized holes. By variation of the excitation density, we are able to directly control the electron hole density and thus determine the efficiency of the BAP spin relaxation mechanism. The electron hole interaction also depends strongly on temperature and hence the temperature dependence of {tau}{sub s}{sup BAP} directly yields a measure for the electron hole interaction strength.

  19. Spin relaxation in submonolayer and monolayer InAs structures grown in a GaAs matrix

    Science.gov (United States)

    Yang, Chunlei; Cui, Xiaodong; Shen, Shun-Qing; Xu, Zhongying; Ge, Weikun

    2009-07-01

    Electron-spin dynamics in InAs/GaAs heterostructures consisting of a single layer of InAs (1/3-1 monolayer) embedded in (001) and (311)A GaAs matrix was studied by means of time-resolved Kerr rotation spectroscopy. The spin-relaxation time of the submonolayer InAs samples is significantly enhanced, compared with that of the monolayer InAs sample. The electron-spin-relaxation time and the effective g factor in submonolayer samples were found to be strongly dependent on the photogenerated carrier density. The contribution from both the D’yakonov-Perel’ mechanism and Bir-Aronov-Pikus mechanism are discussed to interpret the temperature dependence of spin decoherence at various carrier densities.

  20. Clinical and demographic predictors of response to rTMS treatment in unipolar and bipolar depressive disorders.

    Science.gov (United States)

    Rostami, Reza; Kazemi, Reza; Nitsche, Michael A; Gholipour, Fatemeh; Salehinejad, M A

    2017-10-01

    Previous studies investigated predictors of repetitive transcranial magnetic stimulation (rTMS) response in depressive disorders but there is still limited knowledge about clinical predictors. Moreover, predictors of rTMS response in bipolar depression (BDD) are less studied than unipolar depression (UDD). We performed a binary logistic regression analysis in 248 patients with depressive disorders (unipolar N=102, bipolar N=146) who received 20 sessions of DLPFC rTMS (High-frequency rTMS, low-frequency rTMS, bilateral rTMS) to investigate significant clinical and demographic predictors of rTMS response. We also investigated effects of depression type, response (yes, no) and time on reducing somatic and cognitive-affective symptoms of patients. Depression type (unipolar vs. bipolar) did not have a significant effect on rTMS response. 45% of all patients, 51.5% of UDD patients and 41% of BDD patients, responded to rTMS treatment. Age was the only significant demographic predictor of treatment response in all patients. Cognitive-affective symptoms, compared to somatic symptoms were significant predictors for treatment response to rTMS. Common and unique clinical predictor for UDD and BDD were identified. Younger patients and those with cognitive-affective rather than somatic symptoms benefit more from DLPFC rTMS treatment. rTMS is effective in UDD and BDD patients. Patients should be selected based on clinical and demographic profile. Findings are based on the largest thus far reported sample of patients with depressive disorders that received DLPFC rTMS. Copyright © 2017 International Federation of Clinical Neurophysiology. Published by Elsevier B.V. All rights reserved.

  1. Local Noncollinear Spin Analysis.

    Science.gov (United States)

    Abate, Bayileyegn A; Joshi, Rajendra P; Peralta, Juan E

    2017-12-12

    In this work, we generalize the local spin analysis of Clark and Davidson [J. Chem. Phys. 2001 115 (16), 7382] for the partitioning of the expectation value of the molecular spin square operator, ⟨Ŝ 2 ⟩, into atomic contributions, ⟨Ŝ A ·Ŝ B ⟩, to the noncollinear spin case in the framework of density functional theory (DFT). We derive the working equations, and we show applications to the analysis of the noncollinear spin solutions of typical spin-frustrated systems and to the calculation of magnetic exchange couplings. In the former case, we employ the triangular H 3 He 3 test molecule and a Mn 3 complex to show that the local spin analysis provides additional information that complements the standard one-particle spin population analysis. For the calculation of magnetic exchange couplings, J AB , we employ the local spin partitioning to extract ⟨Ŝ A ·Ŝ B ⟩ as a function of the interatomic spin orientation given by the angle θ. This, combined with the dependence of the electronic energy with θ, provides a methodology to extract J AB from DFT calculations that, in contrast to conventional energy differences based methods, does not require the use of ad hoc S A and S B values.

  2. Spin Waves in Terbium

    DEFF Research Database (Denmark)

    Jensen, J.; Houmann, Jens Christian Gylden; Bjerrum Møller, Hans

    1975-01-01

    The energies of spin waves propagating in the c direction of Tb have been studied by inelastic neutron scattering, as a function of a magnetic field applied along the easy and hard directions in the basal plane, and as a function of temperature. From a general spin Hamiltonian, consistent...... with the symmetry, we deduce the dispersion relation for the spin waves in a basal-plane ferromagnet. This phenomenological spin-wave theory accounts for the observed behavior of the magnon energies in Tb. The two q⃗-dependent Bogoliubov components of the magnon energies are derived from the experimental results...

  3. PREFACE: Spin Electronics

    Science.gov (United States)

    Dieny, B.; Sousa, R.; Prejbeanu, L.

    2007-04-01

    Conventional electronics has in the past ignored the spin on the electron, however things began to change in 1988 with the discovery of giant magnetoresistance in metallic thin film stacks which led to the development of a new research area, so called spin-electronics. In the last 10 years, spin-electronics has achieved a number of breakthroughs from the point of view of both basic science and application. Materials research has led to several major discoveries: very large tunnel magnetoresistance effects in tunnel junctions with crystalline barriers due to a new spin-filtering mechanism associated with the spin-dependent symmetry of the electron wave functions new magnetic tunnelling barriers leading to spin-dependent tunnelling barrier heights and acting as spin-filters magnetic semiconductors with increasingly high ordering temperature. New phenomena have been predicted and observed: the possibility of acting on the magnetization of a magnetic nanostructure with a spin-polarized current. This effect, due to a transfer of angular momentum between the spin polarized conduction electrons and the local magnetization, can be viewed as the reciprocal of giant or tunnel magnetoresistance. It can be used to switch the magnetization of a magnetic nanostructure or to generate steady magnetic excitations in the system. the possibility of generating and manipulating spin current without charge current by creating non-equilibrium local accumulation of spin up or spin down electrons. The range of applications of spin electronics materials and phenomena is expanding: the first devices based on giant magnetoresistance were the magnetoresistive read-heads for computer disk drives. These heads, introduced in 1998 with current-in plane spin-valves, have evolved towards low resistance tunnel magnetoresistice heads in 2005. Besides magnetic recording technology, these very sensitive magnetoresistive sensors are finding applications in other areas, in particular in biology. magnetic

  4. Tracking Ultrafast Carrier Dynamics in Single Semiconductor Nanowire Heterostructures

    Directory of Open Access Journals (Sweden)

    Taylor A.J.

    2013-03-01

    Full Text Available An understanding of non-equilibrium carrier dynamics in silicon (Si nanowires (NWs and NW heterostructures is very important due to their many nanophotonic and nanoelectronics applications. Here, we describe the first measurements of ultrafast carrier dynamics and diffusion in single heterostructured Si nanowires, obtained using ultrafast optical microscopy. By isolating individual nanowires, we avoid complications resulting from the broad size and alignment distribution in nanowire ensembles, allowing us to directly probe ultrafast carrier dynamics in these quasi-one-dimensional systems. Spatially-resolved pump-probe spectroscopy demonstrates the influence of surface-mediated mechanisms on carrier dynamics in a single NW, while polarization-resolved femtosecond pump-probe spectroscopy reveals a clear anisotropy in carrier lifetimes measured parallel and perpendicular to the NW axis, due to density-dependent Auger recombination. Furthermore, separating the pump and probe spots along the NW axis enabled us to track space and time dependent carrier diffusion in radial and axial NW heterostructures. These results enable us to reveal the influence of radial and axial interfaces on carrier dynamics and charge transport in these quasi-one-dimensional nanosystems, which can then be used to tailor carrier relaxation in a single nanowire heterostructure for a given application.

  5. Exciton diffusion and dissociation in conjugated polymer/fullerene heterostructures

    NARCIS (Netherlands)

    Markov, D.E.; Amsterdam, E.; Blom, P.W.M.; Sieval, A.B.; Hummelen, J.C.; Heremans, PL; Muccini, M; Hofstraat, H

    2004-01-01

    Time-resolved luminescence spectroscopy has been used to investigate exciton diffusion in thin films of poly(p-phenylene vinylene) (PPV) based derivatives. Exciton density distribution upon photoexcitation in polymer/fullerene heterostructures has been modeled and exciton diffusion length values of

  6. High ionic conductivity in confined bismuth oxide-based heterostructures

    DEFF Research Database (Denmark)

    Sanna, Simone; Esposito, Vincenzo; Christensen, Mogens

    2016-01-01

    Bismuth trioxide in the cubic fluorite phase (δ-Bi2O3) exhibits the highest oxygen ionic conductivity. In this study, we were able to stabilize the pure -Bi2O3 at low temperature with no addition of stabilizer but only by engineering the interface, using highly coherent heterostructures made...

  7. Photosensitive heterostructures made of sulfonamide zinc phthalocyanine and organic semiconductor

    Czech Academy of Sciences Publication Activity Database

    Lutsyk, P.; Vertsimakha, Ya.; Nešpůrek, Stanislav; Pomaz, I.

    2011-01-01

    Roč. 535, - (2011), s. 18-29 ISSN 1542-1406 Institutional research plan: CEZ:AV0Z40500505 Keywords : heterostructure * reversal of sign in photovoltage spectra * sulphonamide-substituted phthalocyanine Subject RIV: CD - Macromolecular Chemistry Impact factor: 0.580, year: 2011

  8. The dielectric genome of van der Waals heterostructures

    DEFF Research Database (Denmark)

    Andersen, Kirsten; Latini, Simone; Thygesen, Kristian Sommer

    2015-01-01

    Vertical stacking of two-dimensional (2D) crystals, such as graphene and hexagonal boron nitride, has recently lead to a new class of materials known as van der Waals heterostructures (vdWHs) with unique and highly tunable electronic properties. Abinitio calculations should in principle provide...

  9. Excitons in van der Waals Heterostructures: A theoretical study

    DEFF Research Database (Denmark)

    Latini, Simone

    Van der Waals heterostructures (vdWHs) represent a novel and largely unexplored class of materials. Since 2013, when Geim and Grigorieva first conceived the stacking of 2D (two-dimensional) materials to create artificial layered structures with tailored properties, a number of promising (opto...

  10. High Photovoltaic Quantum Efficiency in Ultrathin van der Waals Heterostructures.

    Science.gov (United States)

    Wong, Joeson; Jariwala, Deep; Tagliabue, Giulia; Tat, Kevin; Davoyan, Artur R; Sherrott, Michelle C; Atwater, Harry A

    2017-07-25

    We report experimental measurements for ultrathin (van der Waals heterostructures exhibiting external quantum efficiencies exceeding 50% and show that these structures can achieve experimental absorbance >90%. By coupling electromagnetic simulations and experimental measurements, we show that pn WSe 2 /MoS 2 heterojunctions with vertical carrier collection can have internal photocarrier collection efficiencies exceeding 70%.

  11. Effective mechanical properties of multilayer nano-heterostructures.

    Science.gov (United States)

    Mukhopadhyay, T; Mahata, A; Adhikari, S; Zaeem, M Asle

    2017-11-17

    Two-dimensional and quasi-two-dimensional materials are important nanostructures because of their exciting electronic, optical, thermal, chemical and mechanical properties. However, a single-layer nanomaterial may not possess a particular property adequately, or multiple desired properties simultaneously. Recently a new trend has emerged to develop nano-heterostructures by assembling multiple monolayers of different nanostructures to achieve various tunable desired properties simultaneously. For example, transition metal dichalcogenides such as MoS2 show promising electronic and piezoelectric properties, but their low mechanical strength is a constraint for practical applications. This barrier can be mitigated by considering graphene-MoS2 heterostructure, as graphene possesses strong mechanical properties. We have developed efficient closed-form expressions for the equivalent elastic properties of such multi-layer hexagonal nano-hetrostructures. Based on these physics-based analytical formulae, mechanical properties are investigated for different heterostructures such as graphene-MoS2, graphene-hBN, graphene-stanene and stanene-MoS2. The proposed formulae will enable efficient characterization of mechanical properties in developing a wide range of application-specific nano-heterostructures.

  12. Inorganic nanostructure-organic polymer heterostructures useful for thermoelectric devices

    Energy Technology Data Exchange (ETDEWEB)

    See, Kevin C.; Urban, Jeffrey J.; Segalman, Rachel A.; Coates, Nelson E.; Yee, Shannon K.

    2017-11-28

    The present invention provides for an inorganic nanostructure-organic polymer heterostructure, useful as a thermoelectric composite material, comprising (a) an inorganic nanostructure, and (b) an electrically conductive organic polymer disposed on the inorganic nanostructure. Both the inorganic nanostructure and the electrically conductive organic polymer are solution-processable.

  13. Characteristics and heterogeneity of schizoaffective disorder compared with unipolar depression and schizophrenia - a systematic literature review and meta-analysis.

    Science.gov (United States)

    Rink, Lena; Pagel, Tobias; Franklin, Jeremy; Baethge, Christopher

    2016-02-01

    Comparisons of illness characteristics between patients with schizoaffective disorder (SAD) patients and unipolar depression (UD) are rare, even though UD is one of the most important differential diagnoses of SAD. Also, the variability of illness characteristics (heterogeneity) has not been compared. We compared illness characteristics and their heterogeneity among SAD, UD, and - as another important differential diagnosis - schizophrenia (S). In order to reduce sampling bias we systematically searched for studies simultaneously comparing samples of patients with SAD, UD, and S. Using random effects and Mantel-Haenszel models we estimated and compared demographic, illness course and psychopathology parameters, using pooled standard deviations as a measurement of heterogeneity. Out of 155 articles found by an earlier meta-analysis, 765 screened in Medline, 2738 screened in EMBASE, and 855 screened in PsycINFO we selected 24 studies, covering 3714 patients diagnosed according to RDC, DSM-III, DSM-IIIR, DSM-IV, or ICD-10. In almost all key characteristics, samples with schizoaffective disorders fell between unipolar depression and schizophrenia, with a tendency towards schizophrenia. On average, UD patients were significantly older at illness onset (33.0 years, SAD: 25.2, S: 23.4), more often women (59% vs. 57% vs. 39%) and more often married (53% vs. 39% vs. 27%). Their psychopathology was also less severe, as measured by BPRS, GAS, and HAMD. In demographic and clinical variables heterogeneity was roughly 5% larger in UD than in SAD, and samples of patients with schizophrenia had the lowest pooled heterogeneity. A similar picture emerged in a sensitivity analysis with coefficient of variation as the measurement of heterogeneity. Relative to bipolar disorder there are fewer studies including unipolar patients. No studies based on DSM-5 could be included. Regarding unipolar affective disorder this study confirms what we have shown for bipolar disorders in earlier

  14. The effects of centralised and specialised intervention in the early course of severe unipolar depressive disorder: a randomised clinical trial.

    Directory of Open Access Journals (Sweden)

    Hanne Vibe Hansen

    Full Text Available Little is known on whether centralised and specialised combined pharmacological and psychological intervention in the early phase of severe unipolar depression improve prognosis. The aim of the present study was to assess the benefits and harms of centralised and specialised secondary care intervention in the early course of severe unipolar depression.A randomised multicentre trial with central randomisation and blinding in relation to the primary outcome comparing a centralised and specialised outpatient intervention program with standard decentralised psychiatric treatment. The interventions were offered at discharge from first, second, or third hospitalisation due to a single depressive episode or recurrent depressive disorder. The primary outcome was time to readmission to psychiatric hospital. The data on re-hospitalisation was obtained from the Danish Psychiatric Central Register. The secondary and tertiary outcomes were severity of depressive symptoms according to the Major Depression Inventory, adherence to medical treatment, and satisfaction with treatment according to the total score on the Verona Service Satisfaction Scale-Affective Disorder (VSSS-A. These outcomes were assessed using questionnaires one year after discharge from hospital.A total of 268 patients with unipolar depression were included. There was no significant difference in the time to readmission (unadjusted hazard ratio 0.89, 95% confidence interval 0.60 to 1.32; log rank: χ(2 = 0.3, d.f. = 1, p = 0.6; severity of depressive symptoms (mood disorder clinic: median 21.6, quartiles 9.7-31.2 versus standard treatment: median 20.2, quartiles 10.0-29.8; p = 0.7; or the prevalence of patients in antidepressant treatment (73.9% versus 80.0%, p = 0.2. Centralised and specialised secondary care intervention resulted in significantly higher satisfaction with treatment (131 (SD 31.8 versus 107 (SD 25.6; p<0.001.Centralised and specialised secondary care

  15. Modafinil augmentation therapy in unipolar and bipolar depression: a systematic review and meta-analysis of randomized controlled trials.

    Science.gov (United States)

    Goss, Alexander J; Kaser, Muzaffer; Costafreda, Sergi G; Sahakian, Barbara J; Fu, Cynthia H Y

    2013-11-01

    Current pharmacologic treatments for a depressive episode in unipolar major depressive disorder (MDD) and bipolar depression are limited by low rates of remission. Residual symptoms include a persistent low mood and neurovegetative symptoms such as fatigue. The objective of this study was to examine the efficacy and tolerability of augmentation of first-line therapies with the novel stimulant-like agent modafinil in MDD and bipolar depression. MEDLINE/PubMed, PsycINFO, 1980-April 2013 were searched using the following terms: (modafinil or armodafinil) and (depressi* or depressed or major depressive disorder or major depression or unipolar or bipolar or dysthymi*). Inclusion criteria were as follows: randomized controlled trial (RCT) design, sample comprising adult patients (18-65 years) with unipolar or bipolar depression, diagnosis according to DSM-IV, ICD-10, or other well-recognized criteria, modafinil or armodafinil given as augmentation therapy in at least 1 arm of the trial, and publication in English in a peer-reviewed journal. Double-blind, randomized, placebo-controlled clinical trials of adjunctive treatment with modafinil or armodafinil of standard treatment for depressive episodes in MDD and bipolar depression were selected. Two independent appraisers assessed the eligibility of the trials. A random-effects meta-analysis with DerSimonian-Laird method was used. Moderator effects were evaluated by meta-regression. Data from 6 RCTs, with a total of 910 patients with MDD or bipolar depression, consisting of 4 MDD RCTs (n = 568) and 2 bipolar depression RCTs (n = 342) were analyzed. The meta-analysis revealed significant effects of modafinil on improvements in overall depression scores (point estimate = -0.35; 95% CI, -0.61 to -0.10) and remission rates (odds ratio = 1.61; 95% CI, 1.04 to 2.49). The treatment effects were evident in both MDD and bipolar depression, with no difference between disorders. Modafinil showed a significant positive effect on

  16. Reducing the rate and duration of Re- ADMISsions among patients with unipolar disorder and bipolar disorder using smartphone-based monitoring and treatment - the RADMIS trials

    DEFF Research Database (Denmark)

    Faurholt-Jepsen, Maria; Frost, Mads; Martiny, Klaus

    2017-01-01

    Background: Unipolar and bipolar disorder combined account for nearly half of all morbidity and mortality due to mental and substance use disorders, and burden society with the highest health care costs of all psychiatric and neurological disorders. Among these, costs due to psychiatric...... trials aim to investigate whether using a smartphone-based monitoring and treatment system, including an integrated clinical feedback loop, reduces the rate and duration of re-admissions more than standard treatment in unipolar disorder and bipolar disorder. Methods: The RADMIS trials use a randomized...... controlled, single-blind, parallel-group design. Patients with unipolar disorder and patients with bipolar disorder are invited to participate in each trial when discharged from psychiatric hospitals in The Capital Region of Denmark following an affective episode and randomized to either (1...

  17. Enhancement of spin-lattice coupling in nanoengineered oxide films and heterostructures by laser MBE

    Energy Technology Data Exchange (ETDEWEB)

    Xi, Xiaoxing [Temple Univ., Philidelphia, PA (United States)

    2017-06-08

    The objective of the proposed research is to investigate nanoengineered oxide films and multilayer structures that are predicted to show desirable properties. The main focus of the project is an atomic layer-by-layer laser MBE (ALL-Laser MBE ) technique that is superior to the conventional laser MBE in broadening the conditions for the synthesis of high quality nanoscale oxides and new designer materials. In ALL-Laser MBE, separate oxide targets are used instead of one compound target in the conventional laser MBE. The targets are switched back and forth in front of a UV laser beam as they are alternately ablated. The oxide film is thus constructed one atomic layer at a time. The growth of each atomic layer is monitored and controlled by the reflection high energy electron diffraction (RHEED). The intensity of the diffraction spots increases or decreases depending on the chemistry of each atomic layer as well as the surface roughness. This allows us to determine whether the chemical ratio of the different elements in the films meets the desired value and whether each atomic layer is complete. ALL-Laser MBE is versatile: it works for non-polar film on non-polar substrate, polar film on polar substrate, and polar film on non-polar substrate. (In a polar material, each atomic layer is charged whereas in a non-polar material the atomic layers are charge neutral.) It allows one to push the thermodynamic boundary further in stabilizing new phases than reactive MBE and PLD, two of the most successful techniques for oxide thin films. For example, La5Ni4O13, the Ruddlesden-Popper phase with n = 4, has never been reported in the literature because it needs atomic layer-by-layer growth at high oxygen pressures, not possible with other growth techniques. ALL-Laser MBE makes it possible. We have studied the interfacial 2-dimensional electron gas in the LaAlO3/SrTiO3 system, whose mechanism has been a subject of controversy. According to the most prevailing electronic reconstruction mechanism, a positive diverging electric potential is built up in the polar LaAlO3 film when it is grown on a TiO2-terminated SrTiO3 substrate, which is non-polar. This leads to the transfer of half of an electron from the LaAlO3 film surface to SrTiO3 when the LaAlO3 layer is thicker than 4 unit cells, creating a 2D electron gas at the interface with a sheet carrier density of 3.3×1014/cm2 for sufficiently thick LaAlO3. A serious inconsistency with this mechanism is that the carrier densities reported experimentally are invariably lower than the expected value. The most likely reason is that the SrTiO3 substrate is oxygen difficient due to the low oxygen pressures (< 10 mTorr) during growth, and post-growth annealing in oxygen is often used to remove the oxygen vacancies. People cannot grow the LaAlO3 film in higher oxygen pressures - it results in insulating samples or 3D island growth. Because we grow the LaAlO3 film one atomic layer at a time, we were able to grow conducting LaAlO3/SrTiO3 interfaces at a high oxygen pressure with ALL-Laser MBE, as high as 37 mTorr. The high oxygen pressure helps to prevent the possible oxygen reduction in SrTiO3, ensure that the LaAlO3 films are sufficiently oxygenated. Measurements of x-ray linear dichroism (XLD) and x-ray magnetic circular dichroism (XMCD) both show that the spectra of our films are similar to those of well oxygenated samples. In the LaAlO3/SrTiO3 interfaces grown by ALL-Laser MBE at 37 mTorr oxygen pressure, a quantitative agreement between our experimental result and the theoretical prediction was observed, which provides a strong support to the electronic reconstruction mechanism. The key differences between our result and the previous reports are the high oxygen pressure during the film growth and the high film crystallinity. The high oxygen pressure suppresses the likelihood of oxygen vacancies in SrTiO3. Well oxygenated samples produced during film growth can avoid possible defects when sufficient oxygen is provided only after the growth by annealing. Using ALL-Laser MBE, we also synthesized high-quality singlec-rystalline CaMnO3 films. The systematic increase of the oxygen vacancy content in CaMnO3 as a function of applied in-plane strain is observed and confirmed experimentally using high-resolution soft x-ray XAS and hard x-ray photoemission spectroscopy (HAXPES). The relevant defect states in the densities of states are identified and the vacancy content in the films quantified using the combination of first-principles theory and core-hole multiplet calculations with holistic fitting. The strain-induced oxygen-vacancy formation and ordering are a promising avenue for designing and controlling new functionalities in complex transition-metal oxides.

  18. Elastic and piezoelectric properties of zincblende and wurtzite crystalline nanowire heterostructures.

    Science.gov (United States)

    Boxberg, Fredrik; Søndergaard, Niels; Xu, H Q

    2012-09-04

    The elastic and piezoelectric properties of zincblende and wurtzite crystalline InAs/InP nanowire heterostructures have been studied using electro-elastically coupled continuum elasticity theory. A comprehensive comparison of strains, piezoelectric potentials and piezoelectric fields in the two crystal types of nanowire heterostructures is presented. For each crystal type, three different forms of heterostructures-core-shell, axial superlattice, and quantum dot nanowire heterostructures-are considered. In the studied nanowire heterostructures, the principal strains are found to be insensitive to the change in the crystal structure. However, the shear strains in the zincblende and wurtzite nanowire heterostructures can be very different. All the studied nanowire heterostructures are found to exhibit a piezoelectric field along the nanowire axis. The piezoelectric field is in general much stronger in a wurtzite nanowire heterostructure than in its corresponding zincblende heterostructure. Our results are expected to be particularly important for analyzing and understanding the properties of epitaxially grown nanowire heterostructures and for applications in nanowire electronics, optoelectronics, and biochemical sensing. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  19. Elastic and piezoelectric properties of zincblende and wurtzite crystalline nanowire heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Boxberg, Fredrik [Division of Solid State Physics, Lund University (Sweden); Soendergaard, Niels [Division of Mathematical Physics, Lund University (Sweden); Xu, H.Q. [Department of Electronics and Key Laboratory for the Physics and Chemistry of Nanodevices, Peking University, Beijing (China); Division of Solid State Physics, Lund University (Sweden)

    2012-09-04

    The elastic and piezoelectric properties of zincblende and wurtzite crystalline InAs/InP nanowire heterostructures have been studied using electro-elastically coupled continuum elasticity theory. A comprehensive comparison of strains, piezoelectric potentials and piezoelectric fields in the two crystal types of nanowire heterostructures is presented. For each crystal type, three different forms of heterostructures - core-shell, axial superlattice, and quantum dot nanowire heterostructures - are considered. In the studied nanowire heterostructures, the principal strains are found to be insensitive to the change in the crystal structure. However, the shear strains in the zincblende and wurtzite nanowire heterostructures can be very different. All the studied nanowire heterostructures are found to exhibit a piezoelectric field along the nanowire axis. The piezoelectric field is in general much stronger in a wurtzite nanowire heterostructure than in its corresponding zincblende heterostructure. Our results are expected to be particularly important for analyzing and understanding the properties of epitaxially grown nanowire heterostructures and for applications in nanowire electronics, optoelectronics, and biochemical sensing. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  20. Spin Current Noise of the Spin Seebeck Effect and Spin Pumping.

    Science.gov (United States)

    Matsuo, M; Ohnuma, Y; Kato, T; Maekawa, S

    2018-01-19

    We theoretically investigate the fluctuation of a pure spin current induced by the spin Seebeck effect and spin pumping in a normal-metal-(NM-)ferromagnet(FM) bilayer system. Starting with a simple ferromagnet-insulator-(FI-)NM interface model with both spin-conserving and non-spin-conserving processes, we derive general expressions of the spin current and the spin-current noise at the interface within second-order perturbation of the FI-NM coupling strength, and estimate them for a yttrium-iron-garnet-platinum interface. We show that the spin-current noise can be used to determine the effective spin carried by a magnon modified by the non-spin-conserving process at the interface. In addition, we show that it provides information on the effective spin of a magnon, heating at the interface under spin pumping, and spin Hall angle of the NM.

  1. Clinical and Radiographic Outcomes of Unipolar and Bipolar Radial Head Prosthesis in Patients with Radial Head Fracture: A Systemic Review and Meta-Analysis.

    Science.gov (United States)

    Chen, Hongwei; Wang, Ziyang; Shang, Yongjun

    2017-09-13

    To compare clinical outcomes of unipolar and bipolar radial head prosthesis in the treatment of patients with radial head fracture. Medline, Cochrane, EMBASE, Google Scholar databases were searched until April 18, 2016 using the following search terms: radial head fracture, elbow fracture, radial head arthroplasty, implants, prosthesis, unipolar, bipolar, cemented, and press-fit. Randomized controlled trials, retrospective, and cohort studies were included. The Mayo elbow performance score (MEPS), disabilities of the arm, shoulder, and hand (DASH) score, radiologic assessment, ROM, and grip strength following elbow replacement were similar between prosthetic devices. The pooled mean excellent/good ranking of MEPS was 0.78 for unipolar and 0.73 for bipolar radial head arthroplasty, and the pooled mean MEPS was 86.9 and 79.9, respectively. DASH scores for unipolar and bipolar prosthesis were 19.0 and 16.3, respectively. Range of motion outcomes were similar between groups, with both groups have comparable risk of flexion arc, flexion, extension deficit, rotation arc, pronation, and supination (p values bipolar prosthesis). However, bipolar radial head prosthesis was associated with an increased chance of heterotopic ossification and lucency (p values ≤0.049) while unipolar prosthesis was not (p values ≥0.088). Both groups had risk for development of capitellar osteopenia or erosion/wear (p values ≤0.039). Unipolar and bipolar radial head prostheses were similar with respect to clinical outcomes. Additional comparative studies are necessary to further compare different radial head prostheses used to treat radial head fracture.

  2. Quantum spin liquid states

    Science.gov (United States)

    Zhou, Yi; Kanoda, Kazushi; Ng, Tai-Kai

    2017-04-01

    This is an introductory review of the physics of quantum spin liquid states. Quantum magnetism is a rapidly evolving field, and recent developments reveal that the ground states and low-energy physics of frustrated spin systems may develop many exotic behaviors once we leave the regime of semiclassical approaches. The purpose of this article is to introduce these developments. The article begins by explaining how semiclassical approaches fail once quantum mechanics become important and then describe the alternative approaches for addressing the problem. Mainly spin-1 /2 systems are discussed, and most of the time is spent in this article on one particular set of plausible spin liquid states in which spins are represented by fermions. These states are spin-singlet states and may be viewed as an extension of Fermi liquid states to Mott insulators, and they are usually classified in the category of so-called S U (2 ), U (1 ), or Z2 spin liquid states. A review is given of the basic theory regarding these states and the extensions of these states to include the effect of spin-orbit coupling and to higher spin (S >1 /2 ) systems. Two other important approaches with strong influences on the understanding of spin liquid states are also introduced: (i) matrix product states and projected entangled pair states and (ii) the Kitaev honeycomb model. Experimental progress concerning spin liquid states in realistic materials, including anisotropic triangular-lattice systems [κ -(ET )2Cu2(CN )3 and EtMe3Sb [Pd (dmit )2]2 ], kagome-lattice system [ZnCu3(OH )6Cl2 ], and hyperkagome lattice system (Na4 Ir3 O8 ), is reviewed and compared against the corresponding theories.

  3. Spin-spin correlations in ferromagnetic nanosystems

    Science.gov (United States)

    Vedmedenko, E. Y.; Mikuszeit, N.; Stapelfeldt, T.; Wieser, R.; Potthoff, M.; Lichtenstein, A. I.; Wiesendanger, R.

    2011-04-01

    Using exact diagonalization, Monte-Carlo, and mean-field techniques, characteristic temperature scales for ferromagnetic order are discussed for the Ising and the classical anisotropic Heisenberg model on finite lattices in one and two dimensions. The interplay between nearest-neighbor exchange, anisotropy and the presence of surfaces leads, as a function of temperature, to a complex behavior of the distance-dependent spin-spin correlation function, which is very different from what is commonly expected. A finite experimental observation time is considered in addition, which is simulated within the Monte-Carlo approach by an incomplete statistical average. We find strong surface effects for small nanoparticles, which cannot be explained within a simple Landau or mean-field concept and which give rise to characteristic trends of the spin-correlation function in different temperature regimes. Unambiguous definitions of crossover temperatures for finite systems and an effective method to estimate the critical temperature of corresponding infinite systems are given.

  4. Authors' reply to comment on "Are repeated assisted reproductive technology treatments and an unsuccessful outcome risk factors for unipolar depression in infertile women?"

    DEFF Research Database (Denmark)

    Sejbaek, Camilla S.; Pinborg, Anja; Hageman, Ida

    2016-01-01

    . Hence, we did not aim to compare unipolar depression in women who received ART treatment with women who did not. However, a systematic review and meta-analysis (2) was published recently which shows no increased risk of post-partum depressive symptoms in women after medically assisted reproduction......The aim of our national register-based study (1) was to investigate the risk of a new episode of unipolar depression among women treated with assisted reproductive technology (ART) in regards to whether they had achieved a live birth (as a result of treatment or spontaneous conception) or not...

  5. COMPARISON OF UNIPOLAR (MOORE’S PROSTHESIS AND BIPOLAR HEMIARTHROPLASTY IN FRACTURE NECK OF FEMUR IN THE ELDERLY- A SHORT-TERM PROSPECTIVE STUDY

    Directory of Open Access Journals (Sweden)

    Mahendra Bendale

    2016-11-01

    Full Text Available BACKGROUND Femoral neck fractures are common in postmenopausal elderly females as a result of osteoporosis due to trivial trauma or in the young due to high energy trauma. The goal of the surgeon is to return the patient to his/her prefracture functional status. Femoral neck fracture could be impacted and undisplaced or displaced. Femoral neck fractures are also considered “fractures of necessity”, best treated surgically irrespective of displacement. Surgery permits early patient mobilisation and minimises the complications of prolonged recumbence. The bipolar prosthesis has advantage over the unipolar in having two bearings for the movements to occur. This study intends to compare the functional outcome of unipolar Moore’s hemi-replacement and fixed bipolar replacement in elderly patients with fracture neck of femur. In this scenario, the null hypothesis would be that there is no significant difference in the results between the patients treated with Moore’s prosthesis and those treated with bipolar prosthesis. The aim of the study is to compare the results of unipolar and bipolar hemi-arthroplasty for fracture neck of femur in the elderly patients. MATERIALS AND METHODS 30 elderly postmenopausal women with fracture neck femur were included in the study. They were divided into 2 groups and were operated upon by using unipolar and bipolar implants respectively after thorough investigation. The functional outcome was assessed using the Harris Hip Score (HHS. RESULTS Femoral neck fractures belonged to 53.3% with type III fracture and 46.7 had type IV fractures. Fifteen patients had replacement with Austin Moore prosthesis and fifteen patients with bipolar prosthesis. The average HHS at 6 weeks for unipolar and bipolar groups was 65.2 and 66.0, respectively. The average HHS at 12 months for unipolar and bipolar group was 81.0 and 83.6, respectively. 19 (65.5% patients had good HHS at the end of one year. Corrected chi-square value is 2

  6. Spin Switching via Quantum Dot Spin Valves

    Science.gov (United States)

    Gergs, N. M.; Bender, S. A.; Duine, R. A.; Schuricht, D.

    2018-01-01

    We develop a theory for spin transport and magnetization dynamics in a quantum dot spin valve, i.e., two magnetic reservoirs coupled to a quantum dot. Our theory is able to take into account effects of strong correlations. We demonstrate that, as a result of these strong correlations, the dot gate voltage enables control over the current-induced torques on the magnets and, in particular, enables voltage-controlled magnetic switching. The electrical resistance of the structure can be used to read out the magnetic state. Our model may be realized by a number of experimental systems, including magnetic scanning-tunneling microscope tips and artificial quantum dot systems.

  7. A two-colour heterojunction unipolar nanowire light-emitting diode by tunnel injection

    Science.gov (United States)

    Zimmler, Mariano A.; Bao, Jiming; Shalish, Ilan; Yi, Wei; Narayanamurti, Venkatesh; Capasso, Federico

    2007-10-01

    We present a systematic study of the current-voltage characteristics and electroluminescence of gallium nitride (GaN) nanowire on silicon (Si) substrate heterostructures where both semiconductors are n-type. A novel feature of this device is that by reversing the polarity of the applied voltage the luminescence can be selectively obtained from either the nanowire or the substrate. For one polarity of the applied voltage, ultraviolet (and visible) light is generated in the GaN nanowire, while for the opposite polarity infrared light is emitted from the Si substrate. We propose a model, which explains the key features of the data, based on electron tunnelling from the valence band of one semiconductor into the conduction band of the other semiconductor. For example, for one polarity of the applied voltage, given a sufficient potential energy difference between the two semiconductors, electrons can tunnel from the valence band of GaN into the Si conduction band. This process results in the creation of holes in GaN, which can recombine with conduction band electrons generating GaN band-to-band luminescence. A similar process applies under the opposite polarity for Si light emission. This device structure affords an additional experimental handle to the study of electroluminescence in single nanowires and, furthermore, could be used as a novel approach to two-colour light-emitting devices.

  8. Unipolar GaAs AlGaAs mid infrared lasers for spectroscopic applications

    CERN Document Server

    Hvozdara, L

    2000-01-01

    100 mW per facet. The laser emission wavelengths range from 9.5 mu m to 13.2 mu m. The highest maximum operation temperature of T=230 K and the lowest threshold current density of 2.1 kA/cm sup 2 have been achieved among 14 samples presented in this work. A decrease of the threshold current by up to 40 % , and a slight increase of the highest operation temperature have been achieved by fabrication an air-semiconductor photonic bandgap mirror at the ends of a resonator. A FIB Cut coupled cavity quantum cascade laser has been designed and fabricated. An application of GaAs/AlGaAs quantum cascade lasers in the gas spectroscopy is demonstrated. The presented work was aimed to design and to study the electrical and optical properties of GaAs AlGaAs semiconductor heterostructures in order to develop novel coherent radiation sources for the mid infrared band. The main interest is focused on the experimental studies of quantum cascade emitters and lasers. The quantum cascade emitters and lasers are based on the intra...

  9. Unipolar GaAs AlGaAs mid infrared laser for spectroscopic applications

    CERN Document Server

    Hvozdara, L

    2000-01-01

    100 mW per facet. The laser emission wavelengths range from 9.5 mu m to 13.2 mu m. The highest maximum operation temperature of T=230 K and the lowest threshold current density of 2.1 kA/cm sup 2 have been achieved among 14 samples presented in this work. A decrease of the threshold current by up to 40 % , and a slight increase of the highest operation temperature have been achieved by fabrication an air-semiconductor photonic bandgap mirror at the ends of a resonator. A FIB Cut coupled cavity quantum cascade laser has been designed and fabricated. An application of GaAs/AlGaAs quantum cascade lasers in the gas spectroscopy is demonstrated. The presented work was aimed to design and to study the electrical and optical properties of GaAs AlGaAs semiconductor heterostructures in order to develop novel coherent radiation sources for the mid infrared band. The main interest is focused on the experimental studies of quantum cascade emitters and lasers. The quantum cascade emitters and lasers are based on the intra...

  10. Antiferromagnetic spin Seebeck effect.

    Energy Technology Data Exchange (ETDEWEB)

    Wu, Stephen M.; Zhang, Wei; KC, Amit; Borisov, Pavel; Pearson, John E.; Jiang, J. Samuel; Lederman, David; Hoffmann, Axel; Bhattacharya, Anand

    2016-03-03

    We report on the observation of the spin Seebeck effect in antiferromagnetic MnF2. A device scale on-chip heater is deposited on a bilayer of MnF2 (110) (30nm)/Pt (4 nm) grown by molecular beam epitaxy on a MgF2(110) substrate. Using Pt as a spin detector layer, it is possible to measure the thermally generated spin current from MnF2 through the inverse spin Hall effect. The low temperature (2–80 K) and high magnetic field (up to 140 kOe) regime is explored. A clear spin-flop transition corresponding to the sudden rotation of antiferromagnetic spins out of the easy axis is observed in the spin Seebeck signal when large magnetic fields (>9T) are applied parallel to the easy axis of the MnF2 thin film. When the magnetic field is applied perpendicular to the easy axis, the spin-flop transition is absent, as expected.

  11. Spin, mass, and symmetry

    Energy Technology Data Exchange (ETDEWEB)

    Peskin, M.E. [Stanford Univ., CA (United States)

    1994-12-01

    When the strong interactions were a mystery, spin seemed to be just a complication on top of an already puzzling set of phenomena. But now that particle physicists have understood the strong, weak, and electromagnetic interactions, to be gauge theories, with matter built of quarks and leptons, it is recognized that the special properties of spin 1/2 and spin 1 particles have taken central role in the understanding of Nature. The lectures in this summer school will be devoted to the use of spin in unravelling detailed questions about the fundamental interactions. Thus, why not begin by posing a deeper question: Why is there spin? More precisely, why do the basic pointlike constituents of Nature carry intrinsic nonzero quanta of angular momentum? Though the authos has found no definite answer to this question, the pursuit of an answer has led through a wonderful tangle of speculations on the deep structure of Nature. Is spin constructed or is it fundamental? Is it the requirement of symmetry? In the furthest flights taken, it seems that space-time itself is too restrictive a notion, and that this must be generalized in order to gain a full appreciation of spin. In any case, there is no doubt that spin must play a central role in unlocking the mysteries of fundamental physics.

  12. Spin coating of electrolytes

    Science.gov (United States)

    Stetter, Joseph R.; Maclay, G. Jordan

    1989-01-01

    Methods for spin coating electrolytic materials onto substrates are disclosed. More particularly, methods for depositing solid coatings of ion-conducting material onto planar substrates and onto electrodes are disclosed. These spin coating methods are employed to fabricate electrochemical sensors for use in measuring, detecting and quantifying gases and liquids.

  13. Antiferromagnetic Spin Seebeck Effect.

    Science.gov (United States)

    Wu, Stephen M; Zhang, Wei; Kc, Amit; Borisov, Pavel; Pearson, John E; Jiang, J Samuel; Lederman, David; Hoffmann, Axel; Bhattacharya, Anand

    2016-03-04

    We report on the observation of the spin Seebeck effect in antiferromagnetic MnF_{2}. A device scale on-chip heater is deposited on a bilayer of MnF_{2} (110) (30  nm)/Pt (4 nm) grown by molecular beam epitaxy on a MgF_{2} (110) substrate. Using Pt as a spin detector layer, it is possible to measure the thermally generated spin current from MnF_{2} through the inverse spin Hall effect. The low temperature (2-80 K) and high magnetic field (up to 140 kOe) regime is explored. A clear spin-flop transition corresponding to the sudden rotation of antiferromagnetic spins out of the easy axis is observed in the spin Seebeck signal when large magnetic fields (>9  T) are applied parallel to the easy axis of the MnF_{2} thin film. When the magnetic field is applied perpendicular to the easy axis, the spin-flop transition is absent, as expected.

  14. Physics lab in spin

    CERN Multimedia

    Hawkes, N

    1999-01-01

    RAL is fostering commerical exploitation of its research and facilities in two main ways : spin-out companies exploit work done at the lab, spin-in companies work on site taking advantage of the facilities and the expertise available (1/2 page).

  15. Formation of p-Si/ZnO nanowire heterostructures for light emitting devices

    Energy Technology Data Exchange (ETDEWEB)

    Haj Hmeidi, Yaser; Niepelt, Raphael; Gnauck, Martin; Schmidl, Frank; Ronning, Carsten [Institut fuer Festkoerperphysik, Universitaet Jena, Max-Wien-Platz 1, 07743 Jena (Germany)

    2011-07-01

    The development of scalable techniques for assembling nanowire devices needs practical circuits, which are highly parallel and reproducible overlarge areas. ZnO nanowires can be grown easily via vapor-liquid-solid (VLS) mechanism and are suitable for this application. Furthermore, they have an emission wavelength in the UV, but p-type doping is not possible so far. Therefore, light emitting devices must be based on heterostructures with other suitable p-type materials. In this presentation, we demonstrate p-n heterojunctions between n-type ZnO nanowires and highly doped p-type Si substrates. We developed a simple and powerful approach on the basis of spin-on-glass SiO{sub 2}. This approach is intrinsically scalable since every step involved can be carried out in parallel over an entire wafer. The challenge in this particular geometry is the fabrication of top metallic contacts on top of the nanowires in a way that the contact dose not short with the substrate. The resulting devices exhibit rectifying properties and under certain conditions, also light emission.

  16. Ferromagnetic semiconductor-metal transition in heterostructures of electron doped europium monoxide

    Energy Technology Data Exchange (ETDEWEB)

    Stollenwerk, Tobias

    2013-09-15

    In the present work, we develop and solve a self-consistent theory for the description of the simultaneous ferromagnetic semiconductor-metal transition in electron doped Europium monoxide. We investigate two different types of electron doping, Gadolinium impurities and Oxygen vacancies. Besides the conduction band occupation, we can identify low lying spin fluctuations on magnetic impurities as the driving force behind the doping induced enhancement of the Curie temperature. Moreover, we predict the signatures of these magnetic impurities in the spectra of scanning tunneling microscope experiments. By extending the theory to allow for inhomogeneities in one spatial direction, we are able to investigate thin films and heterostructures of Gadolinium doped Europium monoxide. Here, we are able to reproduce the experimentally observed decrease of the Curie temperature with the film thickness. This behavior is attributed to missing coupling partners of the localized 4f moments as well as to an electron depletion at the surface which leads to a reduction of the number of itinerant electrons. By investigating the influence of a metallic substrate onto the phase transition in Gadolinium doped Europium monoxide, we find that the Curie temperature can be increased up to 20%. However, as we show, the underlying mechanism of metal-interface induced charge carrier accumulation is inextricably connected to a suppression of the semiconductor-metal transition.

  17. Quantized conductance doubling and hard gap in a two-dimensional semiconductor-superconductor heterostructure.

    Science.gov (United States)

    Kjaergaard, M; Nichele, F; Suominen, H J; Nowak, M P; Wimmer, M; Akhmerov, A R; Folk, J A; Flensberg, K; Shabani, J; Palmstrøm, C J; Marcus, C M

    2016-09-29

    Coupling a two-dimensional (2D) semiconductor heterostructure to a superconductor opens new research and technology opportunities, including fundamental problems in mesoscopic superconductivity, scalable superconducting electronics, and new topological states of matter. One route towards topological matter is by coupling a 2D electron gas with strong spin-orbit interaction to an s-wave superconductor. Previous efforts along these lines have been adversely affected by interface disorder and unstable gating. Here we show measurements on a gateable InGaAs/InAs 2DEG with patterned epitaxial Al, yielding devices with atomically pristine interfaces between semiconductor and superconductor. Using surface gates to form a quantum point contact (QPC), we find a hard superconducting gap in the tunnelling regime. When the QPC is in the open regime, we observe a first conductance plateau at 4e 2 /h, consistent with theory. The hard-gap semiconductor-superconductor system demonstrated here is amenable to top-down processing and provides a new avenue towards low-dissipation electronics and topological quantum systems.

  18. Low-energy magnetoelectric control of domain states in exchange-coupled heterostructures

    Science.gov (United States)

    Al-Mahdawi, Muftah; Pati, Satya Prakash; Shiokawa, Yohei; Ye, Shujun; Nozaki, Tomohiro; Sahashi, Masashi

    2017-04-01

    The electric manipulation of antiferromagnets has become an area of great interest recently for zero-stray-field spintronic devices, and for their rich spin dynamics. Generally, the application of antiferromagnetic media for information memories and storage requires a heterostructure with a ferromagnetic layer for readout through the exchange-bias field. In magnetoelectric and multiferroic antiferromagnets, the exchange coupling exerts an additional impediment (energy barrier) to magnetization reversal by the applied magnetoelectric energy. We proposed and verified a method to overcome this barrier. We controlled the energy required for switching the magnetic domains in magnetoelectric Cr2O3 films by compensating the exchange-coupling energy from the ferromagnetic layer with the Zeeman energy of a small volumetric spontaneous magnetization found for the sputtered Cr2O3 films. Based on a simplified phenomenological model of the field-cooling process, the magnetic and electric fields required for switching could be tuned. As an example, the switching of antiferromagnetic domains around a zero-threshold electric field was demonstrated at a magnetic field of 2.6 kOe.

  19. Photocontrol of Magnetism above 77 K in Nanoscaled Heterostructures of Cyanometallate Coordination Networks: Mechanism and Limits

    Science.gov (United States)

    Meisel, Mark W.

    2015-03-01

    Using nanometer-sized heterostructures of cyanometallate coordination networks, specifially core@shell nanoparticles of CoFe@CrCr-PBA (PBA = Prussian blue analogues), irradiation by white light at 80 K modifies the magnetic response, and these changes remain intact and persist without continued irradiation to nominally 125 K. Preliminary pressure studies indicate the photoinduced changes can be maintained up to 200 K, the transition temperature of the ferromagnetic CrCr-PBA component. The effect, which we first reported up to 70 K, arises from thermally induced interface strain, which is relaxed by irradiation of the photactive consituent, CoFe-PBA. The ferromagnetic domains in the strained interface region are affected and generate the persistent changes of the magnetism. Our understanding of this photo-magnetostructural mechanism enabled us to extend the phenomenon to include photoactive spin-crossover systems and other ferromagnetic PBAs. The potential path to higher temperatures will be sketched. Presentation is coauthored with Daniel R. Talham, UF Chemistry, and supported by the NSF via DMR-1405439 (DRT), DMR-1202033 (MWM), and DMR-1157490 (NHMFL), and by the UF Division of Sponsored Research.

  20. Numerical solution of multiband k.p model for tunnelling in type-II heterostructures

    Directory of Open Access Journals (Sweden)

    A.E. Botha

    2010-01-01

    Full Text Available A new and very general method was developed for calculating the charge and spin-resolved electron tunnelling in type-II heterojunctions. Starting from a multiband k.p description of the bulk energy-band structure, a multiband k.p Riccati equation was derived. The reflection and transmission coefficients were obtained for each channel by integrating the Riccati equation over the entire heterostructure. Numerical instability was reduced through this method, in which the multichannel log-derivative of the envelope function matrix, rather than the envelope function itself, was propagated. As an example, a six-band k.p Hamiltonian was used to calculate the current-voltage characteristics of a 10-nm wide InAs/ GaSb/InAs single quantum well device which exhibited negative differential resistance at room temperature. The calculated current as a function of applied (bias voltage was found to be in semiquantitative agreement with the experiment, a result which indicated that inelastic transport mechanisms do not contribute significantly to the valley currents measured in this particular device.

  1. Spin Hall and spin swapping torques in diffusive ferromagnets

    KAUST Repository

    Pauyac, C. O.

    2017-12-08

    A complete set of the generalized drift-diffusion equations for a coupled charge and spin dynamics in ferromagnets in the presence of extrinsic spin-orbit coupling is derived from the quantum kinetic approach, covering major transport phenomena, such as the spin and anomalous Hall effects, spin swapping, spin precession and relaxation processes. We argue that the spin swapping effect in ferromagnets is enhanced due to spin polarization, while the overall spin texture induced by the interplay of spin-orbital and spin precessional effects displays a complex spatial dependence that can be exploited to generate torques and nucleate/propagate domain walls in centrosymmetric geometries without use of external polarizers, as opposed to the conventional understanding of spin-orbit mediated torques.

  2. Rapid infusion of esketamine for unipolar and bipolar depression: a retrospective chart review

    Directory of Open Access Journals (Sweden)

    Correia-Melo FS

    2017-06-01

    Full Text Available Fernanda S Correia-Melo,1 Felipe C Argolo,1 Lucas Araújo-de-Freitas,1,2 Gustavo Carneiro Leal,1 Flávio Kapczinski,3 Acioly Luiz Lacerda,4 Lucas C Quarantini1,2 1Psychiatry Service, University Hospital, Federal University of Bahia, Salvador, Brazil; 2Postgraduate Program in Medicine and Health, Federal University of Bahia, Salvador, Brazil; 3Department of Psychiatry, Federal University of Rio Grande do Sul, Porto Alegre, Brazil; 4Department of Psychiatry, Federal University of São Paulo, São Paulo, Brazil Background: This study evaluated efficacy and safety of intravenous subanesthetic doses of esketamine using an administration time of 10 minutes in patients with treatment-resistant depression and bipolar depression.Methods: A retrospective chart review was conducted to identify patients who met the inclusion criteria for treatment-resistant depression and bipolar depression according to Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Text Revision criteria, and these patients received rapid infusion of esketamine between June 2012 and December 2015. The Montgomery–Åsberg Depression Rating Scale (MADRS was administered to measure and score depressive symptom severity before infusion and at 24 hours, 72 hours, and 7 days after infusion. In addition, Clinical Global Impression scale was administered before and 7 days after esketamine infusion.Results: Esketamine was administered to 30 patients. A total of 27 patients met the inclusion criteria and had MADRS evaluation data, which showed that 23 had unipolar and 4 had bipolar depression. Thirteen patients (48.1% showed therapeutic response (MADRS reduction ≥50% within 1 week (7 days of intervention. Remission (MADRS <7 was observed in 10 patients (37.0% in the same period. Therapeutic response and remission frequencies were seen in 16 (59.3% and 11 (40.7% patients, respectively, within 24 hours following drug infusion. The most relevant side effect observed during

  3. Peptidoglycan synthesis machinery in Agrobacterium tumefaciens during unipolar growth and cell division.

    Science.gov (United States)

    Cameron, Todd A; Anderson-Furgeson, James; Zupan, John R; Zik, Justin J; Zambryski, Patricia C

    2014-05-27

    The synthesis of peptidoglycan (PG) in bacteria is a crucial process controlling cell shape and vitality. In contrast to bacteria such as Escherichia coli that grow by dispersed lateral insertion of PG, little is known of the processes that direct polar PG synthesis in other bacteria such as the Rhizobiales. To better understand polar growth in the Rhizobiales Agrobacterium tumefaciens, we first surveyed its genome to identify homologs of (~70) well-known PG synthesis components. Since most of the canonical cell elongation components are absent from A. tumefaciens, we made fluorescent protein fusions to other putative PG synthesis components to assay their subcellular localization patterns. The cell division scaffolds FtsZ and FtsA, PBP1a, and a Rhizobiales- and Rhodobacterales-specific l,d-transpeptidase (LDT) all associate with the elongating cell pole. All four proteins also localize to the septum during cell division. Examination of the dimensions of growing cells revealed that new cell compartments gradually increase in width as they grow in length. This increase in cell width is coincident with an expanded region of LDT-mediated PG synthesis activity, as measured directly through incorporation of exogenous d-amino acids. Thus, unipolar growth in the Rhizobiales is surprisingly dynamic and represents a significant departure from the canonical growth mechanism of E. coli and other well-studied bacilli. Many rod-shaped bacteria, including pathogens such as Brucella and Mycobacteriu, grow by adding new material to their cell poles, and yet the proteins and mechanisms contributing to this process are not yet well defined. The polarly growing plant pathogen Agrobacterium tumefaciens was used as a model bacterium to explore these polar growth mechanisms. The results obtained indicate that polar growth in this organism is facilitated by repurposed cell division components and an otherwise obscure class of alternative peptidoglycan transpeptidases (l

  4. The cumulative load of depressive illness is associated with cognitive function in the remitted state of unipolar depressive disorder.

    Science.gov (United States)

    Hasselbalch, B J; Knorr, U; Hasselbalch, S G; Gade, A; Kessing, L V

    2013-08-01

    To investigate whether the cumulative number, duration and subtypes (severity and presence of psychotic features) of previous episodes of depression in patients with unipolar depressive disorder in a remitted state are associated with decreased global cognitive function. Via the Danish registers individuals between 40 and 80 years of age were identified: (1) patients with a diagnosis of unipolar disorder at their first discharge from a psychiatric hospital in the period 1994 to 2002, and (2) gender and age matched control individuals. The participants were assessed with the Cambridge Cognitive Examination (CAMCOG), which provides a composite measure of global cognitive function. A total of 88 patients and 50 controls accepted our invitation to participate, fulfilled the selection criteria and were included in the study. The cumulative duration of depressive episodes was associated with a decreased CAMCOG score adjusted for age, gender, education, premorbid IQ and residual depressive symptoms (B=-0.14, 95% C.I. (-0.26, -0.02), R(2)adj=0.31, P=.02). Significant associations were also found between CAMCOG score and the cumulative duration and total number of depressive episodes with psychotic features, respectively. Our findings suggest that cognitive dysfunction is associated with the cumulative duration of depressive episodes, and that, in particular, depressive episodes with psychotic features in the course of illness may be a significant predictor of future impairment of cognitive function. Copyright © 2012 Elsevier Masson SAS. All rights reserved.

  5. The Cemented Unipolar Prosthesis for the Management of Displaced Femoral Neck Fractures in the Dependent Osteopenic Elderly.

    Science.gov (United States)

    Grosso, Matthew G; Danoff, Jonathan R; Padgett, Douglas E; Iorio, Richard; Macaulay, William B

    2016-05-01

    Significant variability exists across orthopedic surgeons in the management of the displaced femoral neck fracture in the elderly patient (>75 years old). These patients tend to be less healthy, have inferior bone quality, and gait instability leading to increased risk of periprosthetic fracture, compromised implant fixation, dislocation, and need for revision. The surgeon's goals should be to restore mobility while eliminating pain and need for reoperation. In this review article, we examine the best available evidence in the literature to determine which strategy achieves optimal outcomes. We examine outcome studies comparing use of hemiarthroplasty and total hip arthroplasty, unipolar and bipolar hemiarthroplasty, and cemented vs cementless fixation of femoral stems. For the active, healthy, and lucid patient, or one who has preexisting groin pain, who sustains a displaced femoral neck fracture, the literature supports a total hip arthroplasty. Patients sustaining a displaced femoral neck fracture and who are less active, have decreased bone mass, and are at increased risk of falls would benefit most from a device that optimally balances the need for revision surgery, restores ambulation, and eliminates pain. Thus, the current evidence favors cemented, unipolar hemiarthroplasty for the dependent osteopenic elderly patient with a displaced femoral neck fracture. Copyright © 2016 Elsevier Inc. All rights reserved.

  6. Sociodemographic Correlates of Unipolar Major Depression among the Chinese Elderly in Klang Valley, Malaysia: An Epidemiological Study

    Directory of Open Access Journals (Sweden)

    Rohit Kumar Verma

    2014-01-01

    Full Text Available Background. Depression, as one of the most disabling diseases around the world, had caught the global concern with its rising prevalence rate. There is a growing need of detecting depression, particularly in the old age population which is often left being overlooked. Methods. We conducted a cross-sectional community-based study which included 150 Chinese elderly aged 60 and above within Klang Valley area. We obtained the sociodemographic profiles and assessed the status of well-being, depression, and cognitive function of the participants with the help of instruments: WHO Five-Item Well-Being Index, Major (ICD-10 Depression Inventory, and 6-Item Cognitive Impairment Test. Results. We found that the prevalence of depression among the Chinese elderly within Klang Valley region was 10.7%. With multiple logistic regression, decision to consult doctor on depressed mood or memory problem and presence of cognitive impairment were shown to be significantly associated with unipolar major depression, whereas wellbeing status was also found to be statistically correlated with depression in univariate analysis. Conclusion. The prevalence of unipolar depression among Chinese elderly within Klang Valley, Malaysia presented that there was an increased trend compared to the previous studies.

  7. Synthesis, characterization and photovoltaic integration of type II nanorod heterostructures

    Science.gov (United States)

    McDaniel, Hunter Y.

    Motivated by a desire to control the actions of charges within materials in new and productive ways, researchers have increasingly focused their efforts on engineering materials on the nanometer scale where the laws of quantum mechanics rule supreme. Novel properties emerge when a semiconductor crystal is prepared at sizes below the hydrogenic ground state of the material, also known as the exciton Bohr radius. In addition to effects of quantum confinement, the large fraction of surface atoms can play a significant role in determining nanocrystal properties and applications. By combining two or more nanometer scale semiconductor crystals together to form a nanocrystal heterostructure, new avenues for materials engineering are opened up as nascent properties emerge. The high fraction of surface atoms means that much larger degrees of strain are possible than in the bulk. The large fraction of interface atoms means that the heterojunction properties can dominate the properties of the entire structure. Along with engineering these novel multi component properties comes new unexplored areas of science to be investigated and understood. New techniques are needed for studying these materials that require resolution of features much smaller than the wavelength of (visible) light. Along with this research comes a responsibility to share findings with the scientific community and to pursue directions that can positively impact humanity. At the same time, we should take a long term view when judging the applications of this or any new technology as we are only beginning to understand what is possible. After an introduction to the field in chapter one where we motivate our focus on anisotropic nanocrystal heterostructures, we discuss the formation of Fe3O4/CdS structures from spherical seeds in chapter two. In chapter three we turn our focus to type II CdSe/CdTe nanorod heterostructures where the anisotropy is inherent. The type II system is of particular interest because

  8. Graphene encapsulated gold nanoparticle-quantum dot heterostructures and their electrochemical characterization

    Energy Technology Data Exchange (ETDEWEB)

    Li, Yuan [Metallurgical and Materials Engineering Department, Center for Materials for Information Technology (MINT), The University of Alabama, Tuscaloosa, AL 35487 (United States); Chopra, Nitin, E-mail: nchopra@eng.ua.edu [Metallurgical and Materials Engineering Department, Center for Materials for Information Technology (MINT), The University of Alabama, Tuscaloosa, AL 35487 (United States); Department of Biological Sciences, The University of Alabama, Tuscaloosa, AL 35487 (United States); Department of Chemistry, The University of Alabama, Tuscaloosa, AL 35487 (United States)

    2015-07-30

    Highlights: • Patterning of multilayer graphene shell encapsulated gold nanoparticles (GNPs). • Binding of quantum dots to GNPs resulted in GNP-QD heterostructures. • The heterostructures were characterized for their electrochemical properties. - Abstract: A simple technique for patterning multilayer graphene shell encapsulated gold nanoparticles (GNPs) on the silicon substrate and their further surface decoration with semiconducting quantum dots (QDs) is reported. This leads to the fabrication of a novel silicon electrode decorated with GNP-QD hybrids or heterostructures. The morphology, structure, and composition of the GNPs and GNP-QD heterostructures were evaluated using microscopic and spectroscopic techniques. The heterostructures decorated silicon electrode was also evaluated for the electronic and electrochemical properties. The results showed that the electrical characteristics of the silicon substrate were significantly improved by decorating with GNPs and quantum dots. Furthermore, GNP-QD heterostructure electrode was observed to show significantly increased electrochemical charge transfer activity.

  9. Spin-orbit torque induced spike-timing dependent plasticity

    Energy Technology Data Exchange (ETDEWEB)

    Sengupta, Abhronil, E-mail: asengup@purdue.edu; Al Azim, Zubair; Fong, Xuanyao; Roy, Kaushik [School of Electrical and Computer Engineering, Purdue University, West Lafayette, Indiana 47907 (United States)

    2015-03-02

    Nanoelectronic devices that mimic the functionality of synapses are a crucial requirement for performing cortical simulations of the brain. In this work, we propose a ferromagnet-heavy metal heterostructure that employs spin-orbit torque to implement spike-timing dependent plasticity. The proposed device offers the advantage of decoupled spike transmission and programming current paths, thereby leading to reliable operation during online learning. Possible arrangement of such devices in a crosspoint architecture can pave the way for ultra-dense neural networks. Simulation studies indicate that the device has the potential of achieving pico-Joule level energy consumption (maximum 2 pJ per synaptic event) which is comparable to the energy consumption for synaptic events in biological synapses.

  10. Spin Hall Control of Magnetization in a Perpendicularly-Magnetized Magnetic Insulator

    Science.gov (United States)

    Pai, Chi-Feng; Quindeau, Andy; Tang, Astera; Onbasli, Mehmet; Mann, Maxwell; Caretta, Lucas; Ross, Caroline; Beach, Geoffrey

    Spin Hall effect (SHE)-induced spin-orbit torque (SOT) has been shown to be an efficient mechanism to control the magnetization in magnetic heterostructures. Although numerous works have demonstrated the efficacy of SOT in manipulating the magnetization of ferromagnetic metals (FM), SOT-controlled switching of ferromagnetic insulators (FMIs) has not yet been observed. In this work we show that spin Hall currents in Pt and Ta can generate SOTs strong enough to control the magnetization direction in an adjacent thulium iron garnet FMI film with perpendicular magnetic anisotropy. We find that dc current in the heavy metal (HM) generates an out-of-plane effective field in the FMI consistent with an antidamping torque whose magnitude is comparable to that observed in all-metallic systems. Spin Hall magnetoresistance (SMR) measurements reveal a large spin-mixing conductance, which implies considerable spin transparency at the metal/insulator interface and explains the observed strong current-induced torque. Our results show that charge currents flowing in a HM can be used to both control and detect the magnetization direction in a FMI electrically.

  11. Advanced Semiconductor Heterostructures Novel Devices, Potential Device Applications and Basic Properties

    CERN Document Server

    Stroscio, Michael A

    2003-01-01

    This volume provides valuable summaries on many aspects of advanced semiconductor heterostructures and highlights the great variety of semiconductor heterostructures that has emerged since their original conception. As exemplified by the chapters in this book, recent progress on advanced semiconductor heterostructures spans a truly remarkable range of scientific fields with an associated diversity of applications. Some of these applications will undoubtedly revolutionize critically important facets of modern technology. At the heart of these advances is the ability to design and control the pr

  12. Abnormal room temperature ferromagnetism in CuO-ZnO heterostructures: interface related or not?

    Science.gov (United States)

    Gao, Daqiang; Zhang, Zhipeng; Li, You; Xia, Baorui; Shi, Shoupeng; Xue, Desheng

    2015-01-21

    We report the new functionality of room temperature ferromagnetism in CuO-ZnO heterostructures. Magnetic measurement results indicate the CuO-ZnO heterostructures show enhanced ferromagnetism contrary to the pure CuO (ZnO) and the observed ferromagnetism is proportional to the interface counts for the film-heterostructures, providing proof of interface related ferromagnetism. Our study suggests that magnetically functional interfaces could be an entirely new and novel design of magnetic materials for emergent devices.

  13. Nano-scale polar-nonpolar oxide heterostructures for photocatalysis

    Science.gov (United States)

    Guo, Hongli; Saidi, Wissam A.; Yang, Jinlong; Zhao, Jin

    2016-03-01

    We proposed based on first principles density functional theory calculations that a nano-scale thin film based on a polar-nonpolar transition-metal oxide heterostructure can be used as a highly-efficient photocatalyst. This is demonstrated using a SrTiO3/LaAlO3/SrTiO3 sandwich-like heterostructure with photocatalytic activity in the near-infrared region. The effect of the polar nature of LaAlO3 is two-fold. First, the induced electrostatic field accelerates the photo-generated electrons and holes into opposite directions and minimizes their recombination rates. Hence, the reduction and oxidation reactions can be instigated at the SrTiO3 surfaces located on the opposite sides of the heterostructure. Second, the electric field reduces the band gap of the system making it photoactive in the infrared region. We also show that charge separation can be enhanced by using compressive strain engineering that creates ferroelectric instability in STO. The proposed setup is ideal for tandem oxide photocatalysts especially when combined with photoactive polar materials.We proposed based on first principles density functional theory calculations that a nano-scale thin film based on a polar-nonpolar transition-metal oxide heterostructure can be used as a highly-efficient photocatalyst. This is demonstrated using a SrTiO3/LaAlO3/SrTiO3 sandwich-like heterostructure with photocatalytic activity in the near-infrared region. The effect of the polar nature of LaAlO3 is two-fold. First, the induced electrostatic field accelerates the photo-generated electrons and holes into opposite directions and minimizes their recombination rates. Hence, the reduction and oxidation reactions can be instigated at the SrTiO3 surfaces located on the opposite sides of the heterostructure. Second, the electric field reduces the band gap of the system making it photoactive in the infrared region. We also show that charge separation can be enhanced by using compressive strain engineering that creates

  14. Synthesis and applications of heterostructured semiconductor nanocrystals

    Science.gov (United States)

    Khon, Elena

    Semiconductor nanocrystals (NCs) have been of great interest to researchers for several decades due to their unique optoelectronic properties. These nanoparticles are widely used for a variety of different applications. However, there are many unresolved issues that lower the efficiency and/or stability of devices which incorporate these NCs. Our research is dedicated to addressing these issues by identifying potential problems and resolving them, improving existing systems, generating new synthetic strategies, and/or building new devices. The general strategies for the synthesis of different nanocrystals were established in this work, one of which is the colloidal growth of gold domains onto CdS semiconductor nanocrystals. Control of shape and size was achieved simply by adjusting the temperature and the time of the reaction. Depending on the exact morphology of Au and CdS domains, fabricated nano-composites can undergo evaporation-induced self-assembly onto a substrate, which is very useful for building devices. CdS/Au heterostructures can assemble in two different ways: through end-to-end coupling of Au domains, resulting in the formation of one-dimensional chains; and via side-by-side packing of CdS nanorods, leading to the onset of two-dimensional superlattices. We investigated the nature of exciton-plasmon interactions in Au-tipped CdS nanorods using femtosecond transient absorption spectroscopy. The study demonstrated that the key optoelectronic properties of electrically coupled metal and semiconductor domains are significantly different from those observed in systems with weak inter-domain coupling. In particular, strongly-coupled nanocomposites promote mixing of electronic states at semiconductor-metal domain interfaces, which causes a significant suppression of both plasmon and exciton carrier excitations. Colloidal QDs are starting to replace organic molecules in many different applications, such as organic light emmiting diods (OLEDs), due to their

  15. Nonvolatile transtance change random access memory based on magnetoelectric P(VDF-TrFE)/Metglas heterostructures

    Science.gov (United States)

    Lu, Peipei; Shang, Dashan; Shen, Jianxin; Chai, Yisheng; Yang, Chuansen; Zhai, Kun; Cong, Junzhuang; Shen, Shipeng; Sun, Young

    2016-12-01

    Transtance change random access memory (TCRAM) is a type of nonvolatile memory based on the nonlinear magnetoelectric coupling effects of multiferroics. In this work, ferroelectric P(VDF-TrFE) thin films were prepared on Metglas foil substrates by the sol-gel technique to form multiferroic heterostructures. The magnetoelectric voltage coefficient of the heterostructure can be switched reproducibly to different levels between positive and negative values by applying selective electric-field pulses. Compared with bulk multiferroic heterostructures, the polarization switching voltage was reduced to 7 V. Our facile technological approach enables this organic magnetoelectric heterostructure as a promising candidate for the applications in multilevel TCRAM devices.

  16. In-plane heterostructures of Sb/Bi with high carrier mobility

    Science.gov (United States)

    Zhao, Pei; Wei, Wei; Sun, Qilong; Yu, Lin; Huang, Baibiao; Dai, Ying

    2017-06-01

    In-plane two-dimensional (2D) heterostructures have been attracting public attention due to their distinctive properties. However, the pristine materials that can form in-plane heterostructures are reported only for graphene, hexagonal BN, transition-metal dichalcogenides. It will be of great significance to explore more suitable 2D materials for constructing such ingenious heterostructures. Here, we demonstrate two types of novel seamless in-plane heterostructures combined by pristine Sb and Bi monolayers by means of first-principle approach based on density functional theory. Our results indicate that external strain can serve as an effective strategy for bandgap engineering, and the transition from semiconductor to metal occurs when a compressive strain of -8% is applied. In addition, the designed heterostructures possess direct band gaps with high carrier mobility (˜4000 cm2 V-1 s-1). And the mobility of electrons and holes have huge disparity along the direction perpendicular to the interface of Sb/Bi in-plane heterostructures. It is favorable for carriers to separate spatially. Finally, we find that the band edge positions of Sb/Bi in-plane heterostructures can meet the reduction potential of hydrogen generation in photocatalysis. Our results not only offer alternative materials to construct versatile in-plane heterostructures, but also highlight the applications of 2D in-plane heterostructures in diverse nanodevices and photocatalysis.

  17. Synthesis, optical and electrochemical properties of ZnO nanowires/graphene oxide heterostructures

    National Research Council Canada - National Science Library

    Zeng, Huidan; Cao, Ying; Xie, Shufan; Yang, Junhe; Tang, Zhihong; Wang, Xianying; Sun, Luyi

    2013-01-01

    .... Electrochemical property measurement results demonstrated that the ZnO nanowires/graphene oxide have large integral area of cyclic voltammetry loop, indicating that such heterostructure is promising...

  18. Nanoscale nickel oxide/nickel heterostructures for active hydrogen evolution electrocatalysis

    National Research Council Canada - National Science Library

    Gong, Ming; Zhou, Wu; Tsai, Mon-Che; Zhou, Jigang; Guan, Mingyun; Lin, Meng-Chang; Zhang, Bo; Hu, Yongfeng; Wang, Di-Yan; Yang, Jiang; Pennycook, Stephen J; Hwang, Bing-Joe; Dai, Hongjie

    2014-01-01

    .... Here we report nanoscale nickel oxide/nickel heterostructures formed on carbon nanotube sidewalls as highly effective electrocatalysts for hydrogen evolution reaction with activity similar to platinum...

  19. Observation of long-lived interlayer excitons in monolayer MoSe2-WSe2 heterostructures

    National Research Council Canada - National Science Library

    Rivera, Pasqual; Schaibley, John R; Jones, Aaron M; Ross, Jason S; Wu, Sanfeng; Aivazian, Grant; Klement, Philip; Seyler, Kyle; Clark, Genevieve; Ghimire, Nirmal J; Yan, Jiaqiang; Mandrus, D G; Yao, Wang; Xu, Xiaodong

    2015-01-01

    ..., that is, interlayer excitons. Here, we report the observation of interlayer excitons in monolayer MoSe2-WSe2 heterostructures by photoluminescence and photoluminescence excitation spectroscopy...

  20. Higher spins and holography

    Science.gov (United States)

    Kraus, Per; Ross, Simon F.

    2013-05-01

    The principles of quantum mechanics and relativity impose rigid constraints on theories of massless particles with nonzero spin. Indeed, Yang-Mills theory and General Relativity are the unique solution in the case of spin-1 and spin-2. In asymptotically flat spacetime, there are fundamental obstacles to formulating fully consistent interacting theories of particles of spin greater than 2. However, indications are that such theories are just barely possible in asymptotically anti-de Sitter or de Sitter spacetimes, where the non-existence of an S-matrix provides an escape from the theorems restricting theories in Minkowski spacetime. These higher spin gravity theories are therefore of great intrinsic interest, since they, along with supergravity, provide the only known field theories generalizing the local invariance principles of Yang-Mills theory and General Relativity. While work on higher spin gravity goes back several decades, the subject has gained broader appeal in recent years due to its appearance in the AdS/CFT correspondence. In three and four spacetime dimensions, there exist duality proposals linking higher spin gravity theories to specific conformal field theories living in two and three dimensions respectively. The enlarged symmetry algebra of the conformal field theories renders them exactly soluble, which makes them excellent laboratories for understanding in detail the holographic mechanism behind AdS/CFT duality. Steady progress is also being made on better understanding the space of possible higher spin gravity theories and their physical content. This work includes classifying the possible field multiplets and their interactions, constructing exact solutions of the nonlinear field equations, and relating higher spin theories to string theory. A full understanding of these theories will involve coming to grips with the novel symmetry principles that enlarge those of General Relativity and Yang-Mills theory, and one can hope that this will provide

  1. Spin transfer torque with spin diffusion in magnetic tunnel junctions

    KAUST Repository

    Manchon, Aurelien

    2012-08-09

    Spin transport in magnetic tunnel junctions in the presence of spin diffusion is considered theoretically. Combining ballistic tunneling across the barrier and diffusive transport in the electrodes, we solve the spin dynamics equation in the metallic layers. We show that spin diffusion mixes the transverse spin current components and dramatically modifies the bias dependence of the effective spin transfer torque. This leads to a significant linear bias dependence of the out-of-plane torque, as well as a nonconventional thickness dependence of both spin torque components.

  2. Spin transverse force on spin current in an electric field.

    Science.gov (United States)

    Shen, Shun-Qing

    2005-10-28

    As a relativistic quantum mechanical effect, it is shown that the electron field exerts a transverse force on an electron spin 1/2 only if the electron is moving. The spin force, analogue to the Lorentz for an electron charge in a magnetic field, is perpendicular to the electric field and the spin current whose spin polarization is projected along the electric field. This spin-dependent force can be used to understand the Zitterbewegung of the electron wave packet with spin-orbit coupling and is relevant to the generation of the charge Hall effect driven by the spin current in semiconductors.

  3. Spins in chemistry

    CERN Document Server

    McWeeny, Roy

    2004-01-01

    Originally delivered as a series of lectures, this volume systematically traces the evolution of the ""spin"" concept from its role in quantum mechanics to its assimilation into the field of chemistry. Author Roy McWeeny presents an in-depth illustration of the deductive methods of quantum theory and their application to spins in chemistry, following the path from the earliest concepts to the sophisticated physical methods employed in the investigation of molecular structure and properties. Starting with the origin and development of the spin concept, the text advances to an examination of sp

  4. Quantum Spin Hall Effect

    Energy Technology Data Exchange (ETDEWEB)

    Bernevig, B.Andrei; Zhang, Shou-Cheng; /Stanford U., Phys. Dept.

    2010-01-15

    The quantum Hall liquid is a novel state of matter with profound emergent properties such as fractional charge and statistics. Existence of the quantum Hall effect requires breaking of the time reversal symmetry caused by an external magnetic field. In this work, we predict a quantized spin Hall effect in the absence of any magnetic field, where the intrinsic spin Hall conductance is quantized in units of 2 e/4{pi}. The degenerate quantum Landau levels are created by the spin-orbit coupling in conventional semiconductors in the presence of a strain gradient. This new state of matter has many profound correlated properties described by a topological field theory.

  5. Quantum spin liquids

    Energy Technology Data Exchange (ETDEWEB)

    Mila, Frederic [Institut de Physique Theorique, Universite de Lausanne, BSP, Lausanne (Switzerland)

    2000-11-01

    This paper presents an overview of the properties of magnetic insulators, with emphasis on quantum effects. In particular, the consequences of strong quantum fluctuations on the low-energy properties of a number of systems are reviewed: the occurrence of a spin gap in spin-1 chains and other low-dimensional magnets; the presence of low-lying singlet excitations in several frustrated magnets; the interplay of orbital and spin fluctuations in orbitally degenerate Mott insulators. This review is intended as a pedagogical introduction to the field, and the formalism has been kept at a minimal level. (author)

  6. Frustrated spin systems

    CERN Document Server

    2013-01-01

    This book covers all principal aspects of currently investigated frustrated systems, from exactly solved frustrated models to real experimental frustrated systems, going through renormalization group treatment, Monte Carlo investigation of frustrated classical Ising and vector spin models, low-dimensional systems, spin ice and quantum spin glass. The reader can - within a single book - obtain a global view of the current research development in the field of frustrated systems.This new edition is updated with recent theoretical, numerical and experimental developments in the field of frustrated

  7. Method for estimating spin-spin interactions from magnetization curves

    Science.gov (United States)

    Tamura, Ryo; Hukushima, Koji

    2017-02-01

    We develop a method to estimate the spin-spin interactions in the Hamiltonian from the observed magnetization curve by machine learning based on Bayesian inference. In our method, plausible spin-spin interactions are determined by maximizing the posterior distribution, which is the conditional probability of the spin-spin interactions in the Hamiltonian for a given magnetization curve with observation noise. The conditional probability is obtained with the Markov chain Monte Carlo simulations combined with an exchange Monte Carlo method. The efficiency of our method is tested using synthetic magnetization curve data, and the results show that spin-spin interactions are estimated with a high accuracy. In particular, the relevant terms of the spin-spin interactions are successfully selected from the redundant interaction candidates by the l1 regularization in the prior distribution.

  8. Effectiveness of and Dropout from Outpatient Cognitive Behavioral Therapy for Adult Unipolar Depression: A Meta-Analysis of Nonrandomized Effectiveness Studies

    Science.gov (United States)

    Hans, Eva; Hiller, Wolfgang

    2013-01-01

    Objective: The primary aim of this study was to assess the overall effectiveness of and dropout from individual and group outpatient cognitive behavioral therapy (CBT) for adults with a primary diagnosis of unipolar depressive disorder in routine clinical practice. Method: We conducted a random effects meta-analysis of 34 nonrandomized…

  9. Differences in psychomotor activity in patients suffering from unipolar and bipolar affective disorder in the remitted or mild/moderate depressive state

    DEFF Research Database (Denmark)

    Faurholt-Jepsen, Maria; Brage, Søren; Vinberg, Maj

    2012-01-01

    Abnormalities in psychomotor activity are a central and essential feature of affective disorder. Studies measuring differences in psychomotor activity between unipolar and bipolar disorder show divergent results and none have used a combined heart rate and movement monitor for measuring activity...

  10. Radiation reaction for spinning bodies in effective field theory. II. Spin-spin effects

    Science.gov (United States)

    Maia, Natália T.; Galley, Chad R.; Leibovich, Adam K.; Porto, Rafael A.

    2017-10-01

    We compute the leading post-Newtonian (PN) contributions at quadratic order in the spins to the radiation-reaction acceleration and spin evolution for binary systems, entering at four-and-a-half PN order. Our calculation includes the backreaction from finite-size spin effects, which is presented for the first time. The computation is carried out, from first principles, using the effective field theory framework for spinning extended objects. At this order, nonconservative effects in the spin-spin sector are independent of the spin supplementary conditions. A nontrivial consistency check is performed by showing that the energy loss induced by the resulting radiation-reaction force is equivalent to the total emitted power in the far zone. We find that, in contrast to the spin-orbit contributions (reported in a companion paper), the radiation reaction affects the evolution of the spin vectors once spin-spin effects are incorporated.

  11. Abrupt Schottky Junctions in Al/Ge Nanowire Heterostructures.

    Science.gov (United States)

    Kral, S; Zeiner, C; Stöger-Pollach, M; Bertagnolli, E; den Hertog, M I; Lopez-Haro, M; Robin, E; El Hajraoui, K; Lugstein, A

    2015-07-08

    In this Letter we report on the exploration of axial metal/semiconductor (Al/Ge) nanowire heterostructures with abrupt interfaces. The formation process is enabled by a thermal induced exchange reaction between the vapor-liquid-solid grown Ge nanowire and Al contact pads due to the substantially different diffusion behavior of Ge in Al and vice versa. Temperature-dependent I-V measurements revealed the metallic properties of the crystalline Al nanowire segments with a maximum current carrying capacity of about 0.8 MA/cm(2). Transmission electron microscopy (TEM) characterization has confirmed both the composition and crystalline nature of the pure Al nanowire segments. A very sharp interface between the ⟨111⟩ oriented Ge nanowire and the reacted Al part was observed with a Schottky barrier height of 361 meV. To demonstrate the potential of this approach, a monolithic Al/Ge/Al heterostructure was used to fabricate a novel impact ionization device.

  12. Novel heterostructured Ge nanowires based on polytype transformation.

    Science.gov (United States)

    Vincent, Laetitia; Patriarche, Gilles; Hallais, Géraldine; Renard, Charles; Gardès, Cyrille; Troadec, David; Bouchier, Daniel

    2014-08-13

    We report on a strain-induced phase transformation in Ge nanowires under external shear stresses. The resulted polytype heterostructure may have great potential for photonics and thermoelectric applications. ⟨111⟩-oriented Ge nanowires with standard diamond structure (3C) undergo a phase transformation toward the hexagonal diamond phase referred as the 2H-allotrope. The phase transformation occurs heterogeneously on shear bands along the length of the nanowire. The structure meets the common phenomenological criteria of a martensitic phase transformation. This point is discussed to initiate an on going debate on the transformation mechanisms. The process results in unprecedented quasiperiodic heterostructures 3C/2H along the Ge nanowire. The thermal stability of those 2H domains is also studied under annealing up to 650 °C by in situ TEM.

  13. Photoresponsive memory device based on Graphene/Boron Nitride heterostructure

    Science.gov (United States)

    Kahn, Salman; Velasco, Jairo, Jr.; Ju, Long; Wong, Dillon; Lee, Juwon; Tsai, Hsin Zon; Taniguchi, Takashi; Watanabe, Kenji; Zettl, Alex; Wang, Feng; Crommie, Michael

    2015-03-01

    Recent technological advancements have allowed the stacking of two dimensional layered material in order to create van der Waals heterostructures (VDH), enabling the design of novel properties by exploiting the proximal interaction between layers with different electronic properties. We report the creation of an optoelectronic memory device using a Graphene/Boron Nitride (hBN) heterostructure. Using the photo-induced doping phenomenon, we are able to spatially ``write'' a doping profile on graphene and ``read'' the profile through electrical transport and local probe techniques. We then utilize defect engineering to enhance the optoelectronic response of graphene and explore the effect of defects in hBN. Our work introduces a simple device architecture to create an optoelectronic memory device and contributes towards understanding the proximal effects of hBN on Graphene.

  14. Multifunctional high-performance van der Waals heterostructures

    Science.gov (United States)

    Huang, Mingqiang; Li, Shengman; Zhang, Zhenfeng; Xiong, Xiong; Li, Xuefei; Wu, Yanqing

    2017-12-01

    A range of novel two-dimensional materials have been actively explored for More Moore and More-than-Moore device applications because of their ability to form van der Waals heterostructures with unique electronic properties. However, most of the reported electronic devices exhibit insufficient control of multifunctional operations. Here, we leverage the band-structure alignment properties of narrow-bandgap black phosphorus and large-bandgap molybdenum disulfide to realize vertical heterostructures with an ultrahigh rectifying ratio approaching 106 and on-off ratio up to 107. Furthermore, we design and fabricate tunable multivalue inverters, in which the output logic state and window of the mid-logic can be controlled by specific pairs of channel length and, most importantly, by the electric field, which shifts the band-structure alignment across the heterojunction. Finally, high gains over 150 are achieved in the inverters with optimized device geometries, showing great potential for future logic applications.

  15. Prismatic quantum heterostructures on MBE grown GaAs nanowires

    Energy Technology Data Exchange (ETDEWEB)

    Fontcuberta i Morral, Anna [Walter Schottky Institut, TU Muenchen, Garching (Germany)

    2008-07-01

    Semiconductor nanowires are believed to play a decisive role in the electronic and optoelectronic devices of the XXI century. Their synthesis is a rapidly expanding field, due to the expectations that nanoscale objects and their associated phenomena have to offer to basic and applied science. Here we report on a new method for the growth of GaAs nanowires and related prismatic quantum heterostructures using Molecular Beam Epitaxy (MBE), by avoiding the use of gold as seed for the nanowires. The use of Molecular Beam Epitaxy presents an additional interest, as this technique allows us to produce ultra-pure nanowires and quantum heterostructures on the nanowire facets with very high crystalline quality and atomically sharp interfaces. This new versatility of MBE in the growth of nanostructures opens great possibilities for the generation of novel devices with additional optical and electronic functionalities, as it has been previously shown in planar structures.

  16. Millimeter-wave and optoelectronic applications of heterostructure integrated circuits

    Science.gov (United States)

    Pavlidis, Dimitris

    1991-01-01

    The properties are reviewed of heterostructure devices for microwave-monolithic-integrated circuits (MMICs) and optoelectronic integrated circuits (OICs). Specific devices examined include lattice-matched and pseudomorphic InAlAs/InGaAs high-electron mobility transistors (HEMTs), mixer/multiplier diodes, and heterojunction bipolar transistors (HBTs) developed with a number of materials. MMICs are reviewed that can be employed for amplification, mixing, and signal generation, and receiver/transmitter applications are set forth for OICs based on GaAs and InP heterostructure designs. HEMTs, HBTs, and junction-FETs can be utilized in combination with PIN, MSM, and laser diodes to develop novel communication systems based on technologies that combine microwave and photonic capabilities.

  17. Axial Ge/Si nanowire heterostructure tunnel FETs

    Energy Technology Data Exchange (ETDEWEB)

    Picraux, Sanuel T [Los Alamos National Laboratory; Daych, Shadi A [Los Alamos National Laboratory

    2010-01-01

    The vapor-liquid-solid (VLS) growth of semiconductor nanowires allows doping and composition modulation along their axis and the realization of axial 1 D heterostructures. This provides additional flexibility in energy band-edge engineering along the transport direction which is difficult to attain by planar materials growth and processing techniques. We report here on the design, growth, fabrication, and characterization of asymmetric heterostructure tunnel field-effect transistors (HTFETs) based on 100% compositionally modulated Si/Ge axial NWs for high on-current operation and low ambipolar transport behavior. We discuss the optimization of band-offsets and Schottky barrier heights for high performance HTFETs and issues surrounding their experimental realization. Our HTFET devices with 10 nm PECVD SiN{sub x} gate dielectric resulted in a measured current drive exceeding 100 {mu}A/{mu}m (I/{pi}D) and 10{sup 5} I{sub on}/I{sub off} ratios.

  18. High ionic conductivity in confined bismuth oxide-based heterostructures

    DEFF Research Database (Denmark)

    Sanna, Simone; Esposito, Vincenzo; Christensen, Mogens

    2016-01-01

    Bismuth trioxide in the cubic fluorite phase (δ-Bi2O3) exhibits the highest oxygen ionic conductivity. In this study, we were able to stabilize the pure -Bi2O3 at low temperature with no addition of stabilizer but only by engineering the interface, using highly coherent heterostructures made...... of alternative layers of δ-Bi2O3 and Yttria Stabilized Zirconia (YSZ), deposited by pulsed laser deposition. The resulting [δ-Bi2O3=YSZ] heterostructures are found to be stable over a wide temperature range (500-750 °C) and exhibits stable high ionic conductivity over a long time comparable to the value...... of the pure δ-Bi2O3, which is approximately two orders of magnitude higher than the conductivity of YSZ bulk....

  19. Band structure engineering in topological insulator based heterostructures.

    Science.gov (United States)

    Menshchikova, T V; Otrokov, M M; Tsirkin, S S; Samorokov, D A; Bebneva, V V; Ernst, A; Kuznetsov, V M; Chulkov, E V

    2013-01-01

    The ability to engineer an electronic band structure of topological insulators would allow the production of topological materials with tailor-made properties. Using ab initio calculations, we show a promising way to control the conducting surface state in topological insulator based heterostructures representing an insulator ultrathin films on the topological insulator substrates. Because of a specific relation between work functions and band gaps of the topological insulator substrate and the insulator ultrathin film overlayer, a sizable shift of the Dirac point occurs resulting in a significant increase in the number of the topological surface state charge carriers as compared to that of the substrate itself. Such an effect can also be realized by applying the external electric field that allows a gradual tuning of the topological surface state. A simultaneous use of both approaches makes it possible to obtain a topological insulator based heterostructure with a highly tunable topological surface state.

  20. Optoelectronics based on 2D TMDs and heterostructures

    Science.gov (United States)

    Huo, Nengjie; Yang, Yujue; Li, Jingbo

    2017-03-01

    2D materials including graphene and TMDs have proven interesting physical properties and promising optoelectronic applications. We reviewed the growth, characterization and optoelectronics based on 2D TMDs and their heterostructures, and demonstrated their unique and high quality of performances. For example, we observed the large mobility, fast response and high photo-responsivity in MoS2, WS2 and WSe2 phototransistors, as well as the novel performances in vdW heterostructures such as the strong interlayer coupling, am-bipolar and rectifying behaviour, and the obvious photovoltaic effect. It is being possible that 2D family materials could play an increasingly important role in the future nano- and opto-electronics, more even than traditional semiconductors such as silicon.

  1. Abrupt Schottky Junctions in Al/Ge Nanowire Heterostructures

    OpenAIRE

    Kral, S.; Zeiner, C.; St?ger-Pollach, M.; Bertagnolli, E.; Den Hertog, M.I.; Lopez-Haro, M.; Robin, E.; El Hajraoui, K.; Lugstein, A.

    2015-01-01

    In this Letter we report on the exploration of axial metal/semiconductor (Al/Ge) nanowire heterostructures with abrupt interfaces. The formation process is enabled by a thermal induced exchange reaction between the vapor?liquid?solid grown Ge nanowire and Al contact pads due to the substantially different diffusion behavior of Ge in Al and vice versa. Temperature-dependent I?V measurements revealed the metallic properties of the crystalline Al nanowire segments with a maximum current carrying...

  2. Liquid phase epitaxial growth of heterostructured hierarchical MOF thin films

    KAUST Repository

    Chernikova, Valeriya

    2017-05-10

    Precise control of epitaxial growth of MOF-on-MOF thin films, for ordered hierarchical tbo-type structures is demonstrated. The heterostructured MOF thin film was fabricated by successful sequential deposition of layers from two different MOFs. The 2-periodic layers, edge-transitive 4,4-square lattices regarded as supermolecular building layers, were commendably cross-linked using a combination of inorganic/organic and organic pillars.

  3. Double-heterostructure cavities: from theory to design

    CERN Document Server

    Mahmoodian, Sahand; Poulton, Christopher G; Dossou, Kokou B; Botten, Lindsay C; McPhedran, Ross C; de Sterke, C Martijn

    2012-01-01

    We derive a frequency-domain-based approach for radiation (FAR) from double-heterostructure cavity (DHC) modes. We use this to compute the quality factors and radiation patterns of DHC modes. The semi-analytic nature of our method enables us to provide a general relationship between the radiation pattern of the cavity and its geometry. We use this to provide general designs for ultrahigh quality factor DHCs with radiation patterns that are engineered to emit vertically.

  4. Mixed Dimensional Van der Waals Heterostructures for Opto-Electronics.

    Science.gov (United States)

    Jariwala, Deep

    The isolation of a growing number of two-dimensional (2D) materials has inspired worldwide efforts to integrate distinct 2D materials into van der Waals (vdW) heterostructures. While a tremendous amount of research activity has occurred in assembling disparate 2D materials into ``all-2D'' van der Waals heterostructures, this concept is not limited to 2D materials alone. Given that any passivated, dangling bond-free surface will interact with another via vdW forces, the vdW heterostructure concept can be extended to include the integration of 2D materials with non-2D materials that adhere primarily through noncovalent interactions. In the first part of this talk I will present our work on emerging mixed-dimensional (2D + nD, where n is 0, 1 or 3) heterostructure devices performed at Northwestern University. I will present two distinct examples of gate-tunable p-n heterojunctions 1. Single layer n-type MoS2\\ (2D) combined with p-type semiconducting single walled carbon nanotubes (1D) and 2. Single layer MoS2 combined with 0D molecular semiconductor, pentacene. I will present the unique electrical properties, underlying charge transport mechanisms and photocurrent responses in both the above systems using a variety of scanning probe microscopy techniques as well as computational analysis. This work shows that van der Waals interactions are robust across different dimensionalities of materials and can allow fabrication of semiconductor devices with unique geometries and properties unforeseen in bulk semiconductors. Finally, I will briefly discuss our recent work from Caltech on near-unity absorption in atomically-thin photovoltaic devices. This work is supported by the Materials Research Center at Northwestern University, funded by the National Science Foundation (NSF DMR-1121262) and the Resnick Sustainability Institute at Caltech.

  5. Ag/CdS heterostructural composites: Fabrication, characterizations and photocatalysis

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Yang [Key Laboratory of Interface Science and Engineering in Advanced Materials, Taiyuan University of Technology, Ministry of Education, Taiyuan, Shanxi 030024 (China); College of Materials Science and Engineering, Taiyuan University of Technology, Taiyuan, Shanxi 030024 (China); Chi, Mei [Institute of Metal Research, Chinese Academy of Sciences, Shenyang, Liaoning 110016 (China); Dong, Hailiang; Jia, Husheng; Xu, Bingshe [Key Laboratory of Interface Science and Engineering in Advanced Materials, Taiyuan University of Technology, Ministry of Education, Taiyuan, Shanxi 030024 (China); College of Materials Science and Engineering, Taiyuan University of Technology, Taiyuan, Shanxi 030024 (China); Zhang, Zhuxia, E-mail: zhangzhuxia@tyut.edu.cn [Key Laboratory of Interface Science and Engineering in Advanced Materials, Taiyuan University of Technology, Ministry of Education, Taiyuan, Shanxi 030024 (China); College of Materials Science and Engineering, Taiyuan University of Technology, Taiyuan, Shanxi 030024 (China)

    2014-09-15

    Highlights: • Novel Ag/CdS core–shell heterostructural composites were fabricated using a two-step chemical method. • A formation mechanism of Ag/CdS heterostructural composites. • The photocatalytic activity of Ag/CdS heterostructural composites was found to be improved. • PL emissions are markedly quenched in the Ag/CdS composites than in CdS nanoparticles. - Abstract: Ag/CdS heterostructural materials were successfully synthesized by ultrasound-assisted polyols and hydrothermal method. Under hydrothermal condition, thiourea adsorbed on Ag nanowires releases S{sup 2−} ions, which react with vicinal Cd{sup 2+} ions to form CdS clusters on Ag nanowires. Thereafter, the Ag/CdS composites grow into core–shell structure through CdS aggregation, Ostwald ripening, and preferential growth. The obtained core–shell structures and morphologies were investigated by XRD, SEM, and TEM; the experimental results indicate that the composites are composed of Ag nanowires serving as the core and CdS particles as the shell. The photocatalytic property of Ag/CdS core–shell materials was then investigated in detail. Comparing studies on the degradation of methylene blue were employed by using pure CdS, pure Ag, and Ag/CdS composites, respectively. The results show that the Ag/CdS composites possess higher photocatalytic degradation efficiency. Moreover, the Ag/CdS composites show improved stability, and the photocatalytic activity remains almost unchanged after four recycles. The enhanced photocatalytic effect for Ag/CdS composites is mainly attributed to the photogenerated electron transfer from CdS to Ag nanowire, while photogenerated holes still remain in CdS's valence band. Consequently, the effective separation of photogenerated electrons and holes and the resulting OH radicals improve the photocatalytic efficiency of Ag/CdS composites greatly.

  6. Estimating the spin diffusion length and the spin Hall angle from spin pumping induced inverse spin Hall voltages

    Science.gov (United States)

    Roy, Kuntal

    2017-11-01

    There exists considerable confusion in estimating the spin diffusion length of materials with high spin-orbit coupling from spin pumping experiments. For designing functional devices, it is important to determine the spin diffusion length with sufficient accuracy from experimental results. An inaccurate estimation of spin diffusion length also affects the estimation of other parameters (e.g., spin mixing conductance, spin Hall angle) concomitantly. The spin diffusion length for platinum (Pt) has been reported in the literature in a wide range of 0.5-14 nm, and in particular it is a constant value independent of Pt's thickness. Here, the key reasonings behind such a wide range of reported values of spin diffusion length have been identified comprehensively. In particular, it is shown here that a thickness-dependent conductivity and spin diffusion length is necessary to simultaneously match the experimental results of effective spin mixing conductance and inverse spin Hall voltage due to spin pumping. Such a thickness-dependent spin diffusion length is tantamount to the Elliott-Yafet spin relaxation mechanism, which bodes well for transitional metals. This conclusion is not altered even when there is significant interfacial spin memory loss. Furthermore, the variations in the estimated parameters are also studied, which is important for technological applications.

  7. Vacuum spin squeezing

    Science.gov (United States)

    Hu, Jiazhong; Chen, Wenlan; Vendeiro, Zachary; Urvoy, Alban; Braverman, Boris; Vuletić, Vladan

    2017-11-01

    We investigate the generation of entanglement (spin squeezing) in an optical-transition atomic clock through the coupling to an optical cavity in its vacuum state. We show that if each atom is prepared in a superposition of the ground state and a long-lived electronic excited state, and viewed as a spin-1/2 system, then the collective vacuum light shift entangles the atoms, resulting in a squeezed distribution of the ensemble collective spin, without any light applied. This scheme reveals that even an electromagnetic vacuum can constitute a useful resource for entanglement and quantum manipulation. By rotating the spin direction while coupling to the vacuum, the scheme can be extended to implement two-axis twisting resulting in stronger squeezing.

  8. Silicon takes a spin

    NARCIS (Netherlands)

    Jansen, R.

    An efficient way to transport electron spins from a ferromagnet into silicon essentially makes silicon magnetic, and provides an exciting step towards integration of magnetism and mainstream semiconductor electronics.

  9. Compact photonic spin filters

    Science.gov (United States)

    Ke, Yougang; Liu, Zhenxing; Liu, Yachao; Zhou, Junxiao; Shu, Weixing; Luo, Hailu; Wen, Shuangchun

    2016-10-01

    In this letter, we propose and experimentally demonstrate a compact photonic spin filter formed by integrating a Pancharatnam-Berry phase lens (focal length of ±f ) into a conventional plano-concave lens (focal length of -f). By choosing the input port of the filter, photons with a desired spin state, such as the right-handed component or the left-handed one, propagate alone its original propagation direction, while the unwanted spin component is quickly diverged after passing through the filter. One application of the filter, sorting the spin-dependent components of vector vortex beams on higher-order Poincaré sphere, is also demonstrated. Our scheme provides a simple method to manipulate light, and thereby enables potential applications for photonic devices.

  10. Spin Physics at COMPASS

    CERN Document Server

    Schill, C

    2012-01-01

    The COMPASS experiment is a fixed target experiment at the CERN SPS using muon and hadron beams for the investigation of the spin structure of the nucleon and hadron spectroscopy. The main objective of the muon physics program is the study of the spin of the nucleon in terms of its constituents, quarks and gluons. COMPASS has accumulated data during 6 years scattering polarized muons off a longitudinally or a transversely polarized deuteron (6LiD) or proton (NH3) target. Results for the gluon polarization are obtained from longitudinal double spin cross section asymmetries using two different channels, open charm production and high transverse momentum hadron pairs, both proceeding through the photon-gluon fusion process. Also, the longitudinal spin structure functions of the proton and the deuteron were measured in parallel as well as the helicity distributions for the three lightest quark flavors. With a transversely polarized target, results were obtained with proton and deuteron targets for the Collins an...

  11. Picosecond Spin Seebeck Effect.

    Science.gov (United States)

    Kimling, Johannes; Choi, Gyung-Min; Brangham, Jack T; Matalla-Wagner, Tristan; Huebner, Torsten; Kuschel, Timo; Yang, Fengyuan; Cahill, David G

    2017-02-03

    We report time-resolved magneto-optic Kerr effect measurements of the longitudinal spin Seebeck effect in normal metal/Y_{3}Fe_{5}O_{12} bilayers driven by an interfacial temperature difference between electrons and magnons. The measured time evolution of spin accumulation induced by laser excitation indicates transfer of angular momentum across normal metal/Y_{3}Fe_{5}O_{12} interfaces on a picosecond time scale, too short for contributions from a bulk temperature gradient in an yttrium iron garnet. The product of spin-mixing conductance and the interfacial spin Seebeck coefficient determined is of the order of 10^{8}  A m^{-2} K^{-1}.

  12. Observing Imperfection in Atomic Interfaces for van der Waals Heterostructures

    Science.gov (United States)

    Rooney, Aidan. P.; Kozikov, Aleksey; Rudenko, Alexander N.; Prestat, Eric; Hamer, Matthew J.; Withers, Freddie; Cao, Yang; Novoselov, Kostya S.; Katsnelson, Mikhail I.; Gorbachev, Roman; Haigh, Sarah J.

    2017-09-01

    Vertically stacked van der Waals heterostructures are a lucrative platform for exploring the rich electronic and optoelectronic phenomena in two-dimensional materials. Their performance will be strongly affected by impurities and defects at the interfaces. Here we present the first systematic study of interfaces in van der Waals heterostructure using cross sectional scanning transmission electron microscope (STEM) imaging. By measuring interlayer separations and comparing these to density functional theory (DFT) calculations we find that pristine interfaces exist between hBN and MoS2 or WS2 for stacks prepared by mechanical exfoliation in air. However, for two technologically important transition metal dichalcogenide (TMDC) systems, MoSe2 and WSe2, our measurement of interlayer separations provide the first evidence for impurity species being trapped at buried interfaces with hBN: interfaces which are flat at the nanometer length scale. While decreasing the thickness of encapsulated WSe2 from bulk to monolayer we see a systematic increase in the interlayer separation. We attribute these differences to the thinnest TMDC flakes being flexible and hence able to deform mechanically around a sparse population of protruding interfacial impurities. We show that the air sensitive two dimensional (2D) crystal NbSe2 can be fabricated into heterostructures with pristine interfaces by processing in an inert-gas environment. Finally we find that adopting glove-box transfer significantly improves the quality of interfaces for WSe2 compared to processing in air.

  13. Pulsed laser deposition of yttria stabilized zirconia based heterostructure

    Energy Technology Data Exchange (ETDEWEB)

    Pascu, R. [National Institute for Laser, Plasma and Radiation Physics, 409 Atomistilor Str., PO Box MG-36, Magurele, 077125 Bucharest (Romania); Somacescu, S. [Institute of Physical Chemistry, Romanian Academy, Splaiul Independentei 202, 060021 Bucharest (Romania); Epurescu, G.; Filipescu, M.; Luculescu, C.; Colceag, D. [National Institute for Laser, Plasma and Radiation Physics, 409 Atomistilor Str., PO Box MG-36, Magurele, 077125 Bucharest (Romania); Osiceanu, P. [Institute of Physical Chemistry, Romanian Academy, Splaiul Independentei 202, 060021 Bucharest (Romania); Birjega, R. [National Institute for Laser, Plasma and Radiation Physics, 409 Atomistilor Str., PO Box MG-36, Magurele, 077125 Bucharest (Romania); Mitu, B., E-mail: mitub@infim.ro [National Institute for Laser, Plasma and Radiation Physics, 409 Atomistilor Str., PO Box MG-36, Magurele, 077125 Bucharest (Romania)

    2014-02-28

    Yttria stabilized zirconia (YSZ), nickel-doped yttria stabilized zirconia (NiYSZ) thin films and NiYSZ/YSZ anode–electrolyte heterostructure have been synthesized on Si(100) substrate by pulsed laser deposition technique. Atomic Force Microscopy, Scanning Electron Microscopy, and Variable Angle Spectroscopic Ellipsometry studies have been applied to determine the surface topography, film morphology and thickness. The X-ray diffraction measurements evidenced a highly textured growth along (111) direction for NiYSZ/YSZ heterostructure with crystallite dimension of 18 nm. The X-ray photoelectron spectroscopy analysis showed a displacement of Ni oxidation states along the depth profile, with Ni{sup 3+} oxidation state on the surface, a very thin layer containing Ni{sup 2+} associated to NiO buried under the surface, while metallic Ni is predominant in the bulk. The presence of an intermix layer at the interface between the NiYSZ and YSZ, suggested by the ellipsometric measurements, was confirmed by Secondary Neutral Mass Spectrometry data. - Highlights: • Crystalline NiYSZ/YSZ heterostructure with cubic phase was obtained by PLD at 873 K. • The structure presents an intermix layer at the interface between the NiYSZ and YSZ films. • Ni is present on the surface as Ni{sub 2}O{sub 3}, while in the bulk metallic Ni is predominant.

  14. Structural and Electrical Investigation of C60-Graphene Vertical Heterostructures.

    Science.gov (United States)

    Kim, Kwanpyo; Lee, Tae Hoon; Santos, Elton J G; Jo, Pil Sung; Salleo, Alberto; Nishi, Yoshio; Bao, Zhenan

    2015-06-23

    Graphene, with its unique electronic and structural qualities, has become an important playground for studying adsorption and assembly of various materials including organic molecules. Moreover, organic/graphene vertical structures assembled by van der Waals interaction have potential for multifunctional device applications. Here, we investigate structural and electrical properties of vertical heterostructures composed of C60 thin film on graphene. The assembled film structure of C60 on graphene is investigated using transmission electron microscopy, which reveals a uniform morphology of C60 film on graphene with a grain size as large as 500 nm. The strong epitaxial relations between C60 crystal and graphene lattice directions are found, and van der Waals ab initio calculations support the observed phenomena. Moreover, using C60-graphene heterostructures, we fabricate vertical graphene transistors incorporating n-type organic semiconducting materials with an on/off ratio above 3 × 10(3). Our work demonstrates that graphene can serve as an excellent substrate for assembly of molecules, and attained organic/graphene heterostructures have great potential for electronics applications.

  15. Gating of high-mobility InAs metamorphic heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Shabani, J. [California NanoSystems Institute, University of California, Santa Barbara, California 93106 (United States); McFadden, A. P. [Department of Electrical Engineering, University of California, Santa Barbara, California 93106 (United States); Shojaei, B. [Materials Department, University of California, Santa Barbara, California 93106 (United States); Palmstrøm, C. J. [California NanoSystems Institute, University of California, Santa Barbara, California 93106 (United States); Department of Electrical Engineering, University of California, Santa Barbara, California 93106 (United States); Materials Department, University of California, Santa Barbara, California 93106 (United States)

    2014-12-29

    We investigate the performance of gate-defined devices fabricated on high mobility InAs metamorphic heterostructures. We find that heterostructures capped with In{sub 0.75}Ga{sub 0.25}As often show signs of parallel conduction due to proximity of their surface Fermi level to the conduction band minimum. Here, we introduce a technique that can be used to estimate the density of this surface charge that involves cool-downs from room temperature under gate bias. We have been able to remove the parallel conduction under high positive bias, but achieving full depletion has proven difficult. We find that by using In{sub 0.75}Al{sub 0.25}As as the barrier without an In{sub 0.75}Ga{sub 0.25}As capping, a drastic reduction in parallel conduction can be achieved. Our studies show that this does not change the transport properties of the quantum well significantly. We achieved full depletion in InAlAs capped heterostructures with non-hysteretic gating response suitable for fabrication of gate-defined mesoscopic devices.

  16. Electron dynamics in MoS2-graphite heterostructures.

    Science.gov (United States)

    Zhang, Xinwu; He, Dawei; Yi, Lixin; Zhao, Siqi; He, Jiaqi; Wang, Yongsheng; Zhao, Hui

    2017-10-05

    The electron dynamics in heterostructures formed by multilayer graphite and monolayer or bulk MoS2 were studied by femtosecond transient absorption measurements. Samples of monolayer MoS2-multilayer graphite and bulk MoS2-multilayer graphite were fabricated by exfoliation and dry transfer techniques. Ultrafast laser pulses were used to inject electron-hole pairs into monolayer or bulk MoS2. The transfer of these photocarriers to the adjacent multilayer graphite was time resolved by measuring the differential reflection of a probe pulse. We found that photocarriers injected into monolayer MoS2 transfer to graphite on an ultrafast time scale shorter than 400 fs. Such an efficient charge transfer is key to the development of high performance optoelectronic devices with MoS2 as the light absorbing layer and graphite as electrodes. The absorption coefficient of monolayer MoS2 can be controlled by the carriers in graphite. This process can be used for interlayer coupling and control. In a bulk MoS2-graphite heterostructure, the photocarrier transfer time is about 220 ps, due to the inefficient interlayer charge transport in bulk MoS2. These results provide useful information for developing optoelectronic devices based on MoS2-graphite heterostructures.

  17. Evolutionary design of interfacial phase change van der Waals heterostructures.

    Science.gov (United States)

    Kalikka, Janne; Zhou, Xilin; Behera, Jitendra; Nannicini, Giacomo; Simpson, Robert E

    2016-10-27

    We use an evolutionary algorithm to explore the design space of hexagonal Ge 2 Sb 2 Te 5 ; a van der Waals layered two dimensional crystal heterostructure. The Ge 2 Sb 2 Te 5 structure is more complicated than previously thought. Predominant features include layers of Ge 3 Sb 2 Te 6 and Ge 1 Sb 2 Te 4 two dimensional crystals that interact through Te-Te van der Waals bonds. Interestingly, (Ge/Sb)-Te-(Ge/Sb)-Te alternation is a common feature for the most stable structures of each generation's evolution. This emergent rule provides an important structural motif that must be included in the design of high performance Sb 2 Te 3 -GeTe van der Waals heterostructure superlattices with interfacial atomic switching capability. The structures predicted by the algorithm agree well with experimental measurements on highly oriented, and single crystal Ge 2 Sb 2 Te 5 samples. By analysing the evolutionary algorithm optimised structures, we show that diffusive atomic switching is probable by Ge atoms undergoing a transition at the van der Waals interface from layers of Ge 3 Sb 2 Te 6 to Ge 1 Sb 2 Te 4 thus producing two blocks of Ge 2 Sb 2 Te 5 . Evolutionary methods present an efficient approach to explore the enormous multi-dimensional design parameter space of van der Waals bonded heterostructure superlattices.

  18. Franckeite as a naturally occurring van der Waals heterostructure

    Science.gov (United States)

    Molina-Mendoza, Aday J.; Giovanelli, Emerson; Paz, Wendel S.; Niño, Miguel Angel; Island, Joshua O.; Evangeli, Charalambos; Aballe, Lucía; Foerster, Michael; van der Zant, Herre S. J.; Rubio-Bollinger, Gabino; Agraït, Nicolás; Palacios, J. J.; Pérez, Emilio M.; Castellanos-Gomez, Andres

    2017-01-01

    The fabrication of van der Waals heterostructures, artificial materials assembled by individual stacking of 2D layers, is among the most promising directions in 2D materials research. Until now, the most widespread approach to stack 2D layers relies on deterministic placement methods, which are cumbersome and tend to suffer from poor control over the lattice orientations and the presence of unwanted interlayer adsorbates. Here, we present a different approach to fabricate ultrathin heterostructures by exfoliation of bulk franckeite which is a naturally occurring and air stable van der Waals heterostructure (composed of alternating SnS2-like and PbS-like layers stacked on top of each other). Presenting both an attractive narrow bandgap (<0.7 eV) and p-type doping, we find that the material can be exfoliated both mechanically and chemically down to few-layer thicknesses. We present extensive theoretical and experimental characterizations of the material's electronic properties and crystal structure, and explore applications for near-infrared photodetectors. PMID:28194037

  19. Synthetic Nanosheets of Natural van der Waals Heterostructures.

    Science.gov (United States)

    Banik, Ananya; Biswas, Kanishka

    2017-11-13

    Creation of new van der Waals heterostructures by stacking different two dimensional (2D) crystals on top of each other in a chosen sequence is the next challenge after the discovery of graphene, mono/few layer of h-BN, and transition-metal dichalcogenides. However, chemical syntheses of van der Waals heterostructures are rarer than the physical preparation techniques. Herein, we demonstrate the kinetic stabilization of 2D ultrathin heterostructure (ca. 1.13-2.35 nm thick) nanosheets of layered intergrowth SnBi 2 Te 4 , SnBi 4 Te 7 , and SnBi 6 Te 10 , which belong to the Sn m Bi 2n Te 3n+m homologous series, by a simple solution based synthesis. Few-layer nanosheets exhibit ultralow lattice thermal conductivity (κ lat ) of 0.3-0.5 W m -1  K -1 and semiconducting electron-transport properties with high carrier mobility. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  20. Homogeneous CdTe quantum dots-carbon nanotubes heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Vieira, Kayo Oliveira [Grupo de Pesquisa em Química de Materiais – (GPQM), Departamento de Ciências Naturais, Universidade Federal de São João del-Rei, Campus Dom Bosco, Praça Dom Helvécio, 74, CEP 36301-160, São João del-Rei, MG (Brazil); Bettini, Jefferson [Laboratório Nacional de Nanotecnologia, Centro Nacional de Pesquisa em Energia e Materiais, CEP 13083-970, Campinas, SP (Brazil); Ferrari, Jefferson Luis [Grupo de Pesquisa em Química de Materiais – (GPQM), Departamento de Ciências Naturais, Universidade Federal de São João del-Rei, Campus Dom Bosco, Praça Dom Helvécio, 74, CEP 36301-160, São João del-Rei, MG (Brazil); Schiavon, Marco Antonio, E-mail: schiavon@ufsj.edu.br [Grupo de Pesquisa em Química de Materiais – (GPQM), Departamento de Ciências Naturais, Universidade Federal de São João del-Rei, Campus Dom Bosco, Praça Dom Helvécio, 74, CEP 36301-160, São João del-Rei, MG (Brazil)

    2015-01-15

    The development of homogeneous CdTe quantum dots-carbon nanotubes heterostructures based on electrostatic interactions has been investigated. We report a simple and reproducible non-covalent functionalization route that can be accomplished at room temperature, to prepare colloidal composites consisting of CdTe nanocrystals deposited onto multi-walled carbon nanotubes (MWCNTs) functionalized with a thin layer of polyelectrolytes by layer-by-layer technique. Specifically, physical adsorption of polyelectrolytes such as poly (4-styrene sulfonate) and poly (diallyldimethylammonium chloride) was used to deagglomerate and disperse MWCNTs, onto which we deposited CdTe quantum dots coated with mercaptopropionic acid (MPA), as surface ligand, via electrostatic interactions. Confirmation of the CdTe quantum dots/carbon nanotubes heterostructures was done by transmission and scanning electron microscopies (TEM and SEM), dynamic-light scattering (DLS) together with absorption, emission, Raman and infrared spectroscopies (UV–vis, PL, Raman and FT-IR). Almost complete quenching of the PL band of the CdTe quantum dots was observed after adsorption on the MWCNTs, presumably through efficient energy transfer process from photoexcited CdTe to MWCNTs. - Highlights: • Highly homogeneous CdTe-carbon nanotubes heterostructures were prepared. • Simple and reproducible non-covalent functionalization route. • CdTe nanocrystals homogeneously deposited onto multi-walled carbon nanotubes. • Efficient energy transfer process from photoexcited CdTe to MWCNTs.