Spin injection into Pt-polymers with large spin-orbit coupling

Science.gov (United States)

Sun, Dali; McLaughlin, Ryan; Siegel, Gene; Tiwari, Ashutosh; Vardeny, Z. Valy

2014-03-01

Organic spintronics has entered a new era of devices that integrate organic light-emitting diodes (OLED) in organic spin valve (OSV) geometry (dubbed bipolar organic spin valve, or spin-OLED), for actively manipulating the device electroluminescence via the spin alignment of two ferromagnetic electrodes (Science 337, 204-209, 2012; Appl. Phys. Lett. 103, 042411, 2013). Organic semiconductors that contain heavy metal elements have been widely used as phosphorescent dopants in white-OLEDs. However such active materials are detrimental for OSV operation due to their large spin-orbit coupling (SOC) that may limit the spin diffusion length and thus spin-OLED based on organics with large SOC is a challenge. We report the successful fabrication of OSVs based on pi-conjugated polymers which contain intrachain Platinum atoms (dubbed Pt-polymers). Spin injection into the Pt-polymers is investigated by the giant magnetoresistance (GMR) effect as a function of bias voltage, temperature and polymer layer thickness. From the GMR bias voltage dependence we infer that the ``impendence mismatch'' between ferromagnetic electrodes and Pt-polymer may be suppressed due to the large SOC. Research sponsored by the NSF (Grant No. DMR-1104495) and NSF-MRSEC (DMR 1121252) at the University of Utah.

Charge and Spin Transport in Spin-orbit Coupled and Topological Systems

KAUST Repository

Ndiaye, Papa Birame

2017-01-01

for next-generation technology, three classes of systems that possibly enhance the spin and charge transport efficiency: (i)- topological insulators, (ii)- spin-orbit coupled magnonic systems, (iii)- topological magnetic textures (skyrmions and 3Q magnetic

Spin and tunneling dynamics in an asymmetrical double quantum dot with spin-orbit coupling: Selective spin transport device

Science.gov (United States)

Singh, Madhav K.; Jha, Pradeep K.; Bhattacherjee, Aranya B.

2017-09-01

In this article, we study the spin and tunneling dynamics as a function of magnetic field in a one-dimensional GaAs double quantum dot with both the Dresselhaus and Rashba spin-orbit coupling. In particular, we consider different spatial widths for the spin-up and spin-down electronic states. We find that the spin dynamics is a superposition of slow as well as fast Rabi oscillations. It is found that the Rashba interaction strength as well as the external magnetic field strongly modifies the slow Rabi oscillations which is particularly useful for implementing solid state selective spin transport device.

Spin-orbit torques from interfacial spin-orbit coupling for various interfaces

Science.gov (United States)

Kim, Kyoung-Whan; Lee, Kyung-Jin; Sinova, Jairo; Lee, Hyun-Woo; Stiles, M. D.

2017-09-01

We use a perturbative approach to study the effects of interfacial spin-orbit coupling in magnetic multilayers by treating the two-dimensional Rashba model in a fully three-dimensional description of electron transport near an interface. This formalism provides a compact analytic expression for current-induced spin-orbit torques in terms of unperturbed scattering coefficients, allowing computation of spin-orbit torques for various contexts, by simply substituting scattering coefficients into the formulas. It applies to calculations of spin-orbit torques for magnetic bilayers with bulk magnetism, those with interface magnetism, a normal-metal/ferromagnetic insulator junction, and a topological insulator/ferromagnet junction. It predicts a dampinglike component of spin-orbit torque that is distinct from any intrinsic contribution or those that arise from particular spin relaxation mechanisms. We discuss the effects of proximity-induced magnetism and insertion of an additional layer and provide formulas for in-plane current, which is induced by a perpendicular bias, anisotropic magnetoresistance, and spin memory loss in the same formalism.

Dynamics of Coupled Quantum Spin Chains

International Nuclear Information System (INIS)

Schulz, H.J.

1996-01-01

Static and dynamical properties of weakly coupled antiferromagnetic spin chains are treated using a mean-field approximation for the interchain coupling and exact results for the resulting effective one-dimensional problem. Results for staggered magnetization, Nacute eel temperature, and spin wave excitations are in agreement with experiments on KCuF 3 . The existence of a narrow longitudinal mode is predicted. The results are in agreement with general scaling arguments, contrary to spin wave theory. copyright 1996 The American Physical Society

Current-induced spin polarization in a spin-polarized two-dimensional electron gas with spin-orbit coupling

International Nuclear Information System (INIS)

Wang, C.M.; Pang, M.Q.; Liu, S.Y.; Lei, X.L.

2010-01-01

The current-induced spin polarization (CISP) is investigated in a combined Rashba-Dresselhaus spin-orbit-coupled two-dimensional electron gas, subjected to a homogeneous out-of-plane magnetization. It is found that, in addition to the usual collision-related in-plane parts of CISP, there are two impurity-density-free contributions, arising from intrinsic and disorder-mediated mechanisms. The intrinsic parts of spin polarization are related to the Berry curvature, analogous with the anomalous and spin Hall effects. For short-range collision, the disorder-mediated spin polarizations completely cancel the intrinsic ones and the total in-plane components of CISP equal those for systems without magnetization. However, for remote disorders, this cancellation does not occur and the total in-plane components of CISP strongly depend on the spin-orbit interaction coefficients and magnetization for both pure Rashba and combined Rashba-Dresselhaus models.

Flying spin-qubit gates implemented through Dresselhaus and Rashba spin-orbit couplings

International Nuclear Information System (INIS)

Gong, S.J.; Yang, Z.Q.

2007-01-01

A theoretical scheme is proposed to implement flying spin-qubit gates based on two semiconductor wires with Dresselhaus and Rashba spin-orbit couplings (SOCs), respectively. It is found that under the manipulation of the Dresselhaus/Rashba SOC, spin rotates around x/y axis in the three-dimensional spin space. By combining the two kinds of manipulations, i.e. connecting the two kinds of semiconductor wires in series, we obtain a universal set of losses flying single-qubit gates including Hadamard, phase, and π/8 gates. A ballistic switching effect of electronic flow is also found in the investigation. Our results may be useful in future spin or nanoscale electronics

Pumped double quantum dot with spin-orbit coupling

Directory of Open Access Journals (Sweden)

Sherman Eugene

2011-01-01

Full Text Available Abstract We study driven by an external electric field quantum orbital and spin dynamics of electron in a one-dimensional double quantum dot with spin-orbit coupling. Two types of external perturbation are considered: a periodic field at the Zeeman frequency and a single half-period pulse. Spin-orbit coupling leads to a nontrivial evolution in the spin and orbital channels and to a strongly spin- dependent probability density distribution. Both the interdot tunneling and the driven motion contribute into the spin evolution. These results can be important for the design of the spin manipulation schemes in semiconductor nanostructures. PACS numbers: 73.63.Kv,72.25.Dc,72.25.Pn

Current-induced torques and interfacial spin-orbit coupling

KAUST Repository

Haney, Paul M.; Lee, Hyun-Woo; Lee, Kyung-Jin; Manchon, Aurelien; Stiles, M. D.

2013-01-01

In bilayer systems consisting of an ultrathin ferromagnetic layer adjacent to a metal with strong spin-orbit coupling, an applied in-plane current induces torques on the magnetization. The torques that arise from spin-orbit coupling are of particular interest. Here we use first-principles methods to calculate the current-induced torque in a Pt-Co bilayer to help determine the underlying mechanism. We focus exclusively on the analog to the Rashba torque, and do not consider the spin Hall effect. The details of the torque depend strongly on the layer thicknesses and the interface structure, providing an explanation for the wide variation in results found by different groups. The torque depends on the magnetization direction in a way similar to that found for a simple Rashba model. Artificially turning off the exchange spin splitting and separately the spin-orbit coupling potential in the Pt shows that the primary source of the “fieldlike” torque is a proximate spin-orbit effect on the Co layer induced by the strong spin-orbit coupling in the Pt.

Current-induced torques and interfacial spin-orbit coupling

KAUST Repository

Haney, Paul M.

2013-12-19

In bilayer systems consisting of an ultrathin ferromagnetic layer adjacent to a metal with strong spin-orbit coupling, an applied in-plane current induces torques on the magnetization. The torques that arise from spin-orbit coupling are of particular interest. Here we use first-principles methods to calculate the current-induced torque in a Pt-Co bilayer to help determine the underlying mechanism. We focus exclusively on the analog to the Rashba torque, and do not consider the spin Hall effect. The details of the torque depend strongly on the layer thicknesses and the interface structure, providing an explanation for the wide variation in results found by different groups. The torque depends on the magnetization direction in a way similar to that found for a simple Rashba model. Artificially turning off the exchange spin splitting and separately the spin-orbit coupling potential in the Pt shows that the primary source of the “fieldlike” torque is a proximate spin-orbit effect on the Co layer induced by the strong spin-orbit coupling in the Pt.

Pure spin current manipulation in antiferromagnetically exchange coupled heterostructures

Science.gov (United States)

Avilés-Félix, L.; Butera, A.; González-Chávez, D. E.; Sommer, R. L.; Gómez, J. E.

2018-03-01

We present a model to describe the spin currents generated by ferromagnet/spacer/ferromagnet exchange coupled trilayer systems and heavy metal layers with strong spin-orbit coupling. By exploiting the magnitude of the exchange coupling (oscillatory RKKY-like coupling) and the spin-flop transition in the magnetization process, it has been possible to produce spin currents polarized in arbitrary directions. The spin-flop transition of the trilayer system originates pure spin currents whose polarization vector depends on the exchange field and the magnetization equilibrium angles. We also discuss a protocol to control the polarization sign of the pure spin current injected into the metallic layer by changing the initial conditions of magnetization of the ferromagnetic layers previously to the spin pumping and inverse spin Hall effect experiments. The small differences in the ferromagnetic layers lead to a change in the magnetization vector rotation that permits the control of the sign of the induced voltage components due to the inverse spin Hall effect. Our results can lead to important advances in hybrid spintronic devices with new functionalities, particularly, the ability to control microscopic parameters such as the polarization direction and the sign of the pure spin current through the variation of macroscopic parameters, such as the external magnetic field or the thickness of the spacer in antiferromagnetic exchange coupled systems.

Coupled spin and charge collective excitations in a spin polarized electron gas

International Nuclear Information System (INIS)

Marinescu, D.C.; Quinn, J.J.; Yi, K.S.

1997-01-01

The charge and longitudinal spin responses induced in a spin polarized quantum well by a weak electromagnetic field are investigated within the framework of the linear response theory. The authors evaluate the excitation frequencies for the intra- and inter-subband transitions of the collective charge and longitudinal spin density oscillations including many-body corrections beyond the random phase approximation through the spin dependent local field factors, G σ ± (q,ω). An equation-of-motion method was used to obtain these corrections in the limit of long wavelengths, and the results are given in terms of the equilibrium pair correlation function. The finite degree of spin polarization is shown to introduce coupling between the charge and spin density modes, in contrast with the result for an unpolarized system

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.

Large spin accumulation due to spin-charge coupling across a break-junction

Science.gov (United States)

Chen, Shuhan; Zou, Han; Chui, Siu-Tat; Ji, Yi

2013-03-01

We investigate large spin signals in break-junction nonlocal spin valves (NLSV). The break-junction is a nanometer-sized vacuum tunneling gap between the spin detector and the nonmagnetic channel, formed by electro-static discharge. The spin signals can be either inverted or non-inverted and the magnitudes are much larger than those of standard NLSV. Spin signals with high percentage values (10% - 0%) have been observed. When the frequency of the a.c. modulation is varied, the absolute magnitudes of signals remain the same although the percentage values change. These observations affirm the nonlocal nature of the measurements and rule out local magnetoresistive effects. Owing to the spin-charge coupling across the break-junction, the spin accumulation in a ferromagnet splits into two terms. One term decays on the charge screening length (0.1 nm) and the other decays on the spin diffusion length (10 nm nm). The magnitude of the former is proportional to the resistance of the junction. Therefore a highly resistive break-junction leads to a large spin accumulation and thereby a large spin signal. The signs of the spin signal are determined by the relationship between spin-dependent conductivities, diffusion constants, and density of states of the ferromagnet. This work was supported by US DOE grant No. DE-FG02-07ER46374.

Mode coupling in spin torque oscillators

International Nuclear Information System (INIS)

Zhang, Steven S.-L.; Zhou, Yan; Li, Dong; Heinonen, Olle

2016-01-01

A number of recent experimental works have shown that the dynamics of a single spin torque oscillator can exhibit complex behavior that stems from interactions between two or more modes of the oscillator, such as observed mode-hopping or mode coexistence. There has been some initial work indicating how the theory for a single-mode (macro-spin) spin torque oscillator should be generalized to include several modes and the interactions between them. In the present work, we rigorously derive such a theory starting with the Landau–Lifshitz–Gilbert equation for magnetization dynamics by expanding up to third-order terms in deviation from equilibrium. Our results show how a linear mode coupling, which is necessary for observed mode-hopping to occur, arises through coupling to a magnon bath. The acquired temperature dependence of this coupling implies that the manifold of orbits and fixed points may shift with temperature. - Highlights: • Deriving equations for coupled modes in spin torque oscillators. • Including Hamiltonian formalism and elimination of three–magnon processes. • Thermal bath of magnons central to mode coupling. • Numerical examples of circular and elliptical devices.

Mode coupling in spin torque oscillators

Energy Technology Data Exchange (ETDEWEB)

Zhang, Steven S.-L., E-mail: ZhangShule@missouri.edu [Department of Physics and Astronomy, University of Missouri, Columbia, MO 65211 (United States); Zhou, Yan, E-mail: yanzhou@hku.hk [Department of Physics, The University of Hong Kong, Hong Kong (China); Center of Theoretical and Computational Physics, University of Hong Kong, Hong Kong (China); Li, Dong, E-mail: geodesic.ld@gmail.com [Department of Physics, Centre for Nonlinear Studies, and Beijing-Hong Kong-Singapore Joint Centre for Nonlinear and Complex Systems, Hong Kong Baptist University, Kowloon Tong, Hong Kong (China); Heinonen, Olle, E-mail: heinonen@anl.gov [Material Science Division, Argonne National Laboratory, Lemont, IL 60439 (United States); Northwestern-Argonne Institute of Science and Technology, 2145 Sheridan Road, Evanston, IL 60208 (United States); Computation Institute, The Unversity of Chicago, 5735 S Ellis Avenue, Chicago, IL 60637 (United States)

2016-09-15

A number of recent experimental works have shown that the dynamics of a single spin torque oscillator can exhibit complex behavior that stems from interactions between two or more modes of the oscillator, such as observed mode-hopping or mode coexistence. There has been some initial work indicating how the theory for a single-mode (macro-spin) spin torque oscillator should be generalized to include several modes and the interactions between them. In the present work, we rigorously derive such a theory starting with the Landau–Lifshitz–Gilbert equation for magnetization dynamics by expanding up to third-order terms in deviation from equilibrium. Our results show how a linear mode coupling, which is necessary for observed mode-hopping to occur, arises through coupling to a magnon bath. The acquired temperature dependence of this coupling implies that the manifold of orbits and fixed points may shift with temperature. - Highlights: • Deriving equations for coupled modes in spin torque oscillators. • Including Hamiltonian formalism and elimination of three–magnon processes. • Thermal bath of magnons central to mode coupling. • Numerical examples of circular and elliptical devices.

Nonlinear spin wave coupling in adjacent magnonic crystals

Energy Technology Data Exchange (ETDEWEB)

Sadovnikov, A. V., E-mail: sadovnikovav@gmail.com; Nikitov, S. A. [Laboratory “Metamaterials,” Saratov State University, Saratov 410012 (Russian Federation); Kotel' nikov Institute of Radioengineering and Electronics, Russian Academy of Sciences, Moscow 125009 (Russian Federation); Beginin, E. N.; Morozova, M. A.; Sharaevskii, Yu. P.; Grishin, S. V.; Sheshukova, S. E. [Laboratory “Metamaterials,” Saratov State University, Saratov 410012 (Russian Federation)

2016-07-25

We have experimentally studied the coupling of spin waves in the adjacent magnonic crystals. Space- and time-resolved Brillouin light-scattering spectroscopy is used to demonstrate the frequency and intensity dependent spin-wave energy exchange between the side-coupled magnonic crystals. The experiments and the numerical simulation of spin wave propagation in the coupled periodic structures show that the nonlinear phase shift of spin wave in the adjacent magnonic crystals leads to the nonlinear switching regime at the frequencies near the forbidden magnonic gap. The proposed side-coupled magnonic crystals represent a significant advance towards the all-magnonic signal processing in the integrated magnonic circuits.

Nonlinear spin wave coupling in adjacent magnonic crystals

International Nuclear Information System (INIS)

Sadovnikov, A. V.; Nikitov, S. A.; Beginin, E. N.; Morozova, M. A.; Sharaevskii, Yu. P.; Grishin, S. V.; Sheshukova, S. E.

2016-01-01

We have experimentally studied the coupling of spin waves in the adjacent magnonic crystals. Space- and time-resolved Brillouin light-scattering spectroscopy is used to demonstrate the frequency and intensity dependent spin-wave energy exchange between the side-coupled magnonic crystals. The experiments and the numerical simulation of spin wave propagation in the coupled periodic structures show that the nonlinear phase shift of spin wave in the adjacent magnonic crystals leads to the nonlinear switching regime at the frequencies near the forbidden magnonic gap. The proposed side-coupled magnonic crystals represent a significant advance towards the all-magnonic signal processing in the integrated magnonic circuits.

Spin reorientation via antiferromagnetic coupling

Energy Technology Data Exchange (ETDEWEB)

Ranjbar, M., E-mail: mojtaba.ranjbar@physics.gu.se [Data Storage Institute, A-STAR (Agency for Science, Technology and Research), 5, Engineering Drive 1, Singapore 117608 (Singapore); Department of Physics, University of Gothenburg, 412 96 Gothenburg (Sweden); Sbiaa, R. [Data Storage Institute, A-STAR (Agency for Science, Technology and Research), 5, Engineering Drive 1, Singapore 117608 (Singapore); Department of Physics, Sultan Qaboos University, P.O. Box 36, PC 123, Muscat (Oman); Dumas, R. K. [Department of Physics, University of Gothenburg, 412 96 Gothenburg (Sweden); Åkerman, J. [Department of Physics, University of Gothenburg, 412 96 Gothenburg (Sweden); Materials Physics, School of ICT, Royal Institute of Technology (KTH), 164 40 Kista (Sweden); Piramanayagam, S. N. [Data Storage Institute, A-STAR (Agency for Science, Technology and Research), 5, Engineering Drive 1, Singapore 117608 (Singapore)

2014-05-07

Spin reorientation in antiferromagnetically coupled (AFC) Co/Pd multilayers, wherein the thickness of the constituent Co layers was varied, was studied. AFC-Co/Pd multilayers were observed to have perpendicular magnetic anisotropy even for a Co sublayer thickness of 1 nm, much larger than what is usually observed in systems without antiferromagnetic coupling. When similar multilayer structures were prepared without antiferromagnetic coupling, this effect was not observed. The results indicate that the additional anisotropy energy contribution arising from the antiferromagnetic coupling, which is estimated to be around 6 × 10{sup 6} ergs/cm{sup 3}, induces the spin-reorientation.

Detecting the multi-spin interaction of an XY spin chain by the geometric phase of a coupled qubit

International Nuclear Information System (INIS)

Zhang, Xiu-xing; Zhang, Ai-ping; Li, Fu-li

2012-01-01

We investigate geometric phase (GP) of a qubit symmetrically coupled to a XY spin chain with three-spin interaction in a transverse magnetic field. An analytical expression for the GP is found in the weak coupling limit. It is shown that the GP displays a sharp peak or dip around the quantum phase transition point of the spin chain. Without the three-spin interaction, the GP has a peak or dip around the critical point λ=1. If the three-spin interaction exists, the peak or dip position is obviously shifted away from the original position. This result reveals that the GP may be taken as an observable to detect both the existence and strength of multi-spin interaction in a spin chain. -- Highlights: ► Analytical expression for geometric phase (GP) of a qubit coupled to a spin chain is obtained. ► Relation between GP and multi-spin interaction is investigated. ► Detection of multi-spin interaction by means of GP is proposed.

Hydrodynamics of Normal Atomic Gases with Spin-orbit Coupling.

Science.gov (United States)

Hou, Yan-Hua; Yu, Zhenhua

2015-10-20

Successful realization of spin-orbit coupling in atomic gases by the NIST scheme opens the prospect of studying the effects of spin-orbit coupling on many-body physics in an unprecedentedly controllable way. Here we derive the linearized hydrodynamic equations for the normal atomic gases of the spin-orbit coupling by the NIST scheme with zero detuning. We show that the hydrodynamics of the system crucially depends on the momentum susceptibilities which can be modified by the spin-orbit coupling. We reveal the effects of the spin-orbit coupling on the sound velocities and the dipole mode frequency of the gases by applying our formalism to the ideal Fermi gas. We also discuss the generalization of our results to other situations.

Spin relaxation near the metal-insulator transition: dominance of the Dresselhaus spin-orbit coupling.

Science.gov (United States)

Intronati, Guido A; Tamborenea, Pablo I; Weinmann, Dietmar; Jalabert, Rodolfo A

2012-01-06

We identify the Dresselhaus spin-orbit coupling as the source of the dominant spin-relaxation mechanism in the impurity band of a wide class of n-doped zinc blende semiconductors. The Dresselhaus hopping terms are derived and incorporated into a tight-binding model of impurity sites, and they are shown to unexpectedly dominate the spin relaxation, leading to spin-relaxation times in good agreement with experimental values. This conclusion is drawn from two complementary approaches: an analytical diffusive-evolution calculation and a numerical finite-size scaling study of the spin-relaxation time.

Symmetry rules for the indirect nuclear spin-spin coupling tensor revisited

Science.gov (United States)

Buckingham, A. D.; Pyykkö, P.; Robert, J. B.; Wiesenfeld, L.

The symmetry rules of Buckingham and Love (1970), relating the number of independent components of the indirect spin-spin coupling tensor J to the symmetry of the nuclear sites, are shown to require modification if the two nuclei are exchanged by a symmetry operation. In that case, the anti-symmetric part of J does not transform as a second-rank polar tensor under symmetry operations that interchange the coupled nuclei and may be called an anti-tensor. New rules are derived and illustrated by simple molecular models.

Selective coupling of individual electron and nuclear spins with integrated all-spin coherence protection

Science.gov (United States)

Terletska, Hanna; Dobrovitski, Viatcheslav

2015-03-01

The electron spin of the NV center in diamond is a promising platform for spin sensing. Applying the dynamical decoupling, the NV electron spin can be used to detect the individual weakly coupled carbon-13 nuclear spins in diamond and employ them for small-scale quantum information processing. However, the nuclear spins within this approach remain unprotected from decoherence, which ultimately limits the detection and restricts the fidelity of the quantum operation. Here we investigate possible schemes for combining the resonant decoupling on the NV spin with the decoherence protection of the nuclear spins. Considering several schemes based on pulse and continuous-wave decoupling, we study how the joint electron-nuclear spin dynamics is affected. We identify regimes where the all-spin coherence protection improves the detection and manipulation. We also discuss potential applications of the all-spin decoupling for detecting spins outside diamond, with the purpose of implementing the nanoscale NMR. This work was supported by the US Department of Energy Basic Energy Sciences (Contract No. DE-AC02-07CH11358).

Inverse engineering for fast transport and spin control of spin-orbit-coupled Bose-Einstein condensates in moving harmonic traps

Science.gov (United States)

Chen, Xi; Jiang, Ruan-Lei; Li, Jing; Ban, Yue; Sherman, E. Ya.

2018-01-01

We investigate fast transport and spin manipulation of tunable spin-orbit-coupled Bose-Einstein condensates in a moving harmonic trap. Motivated by the concept of shortcuts to adiabaticity, we design inversely the time-dependent trap position and spin-orbit-coupling strength. By choosing appropriate boundary conditions we obtain fast transport and spin flip simultaneously. The nonadiabatic transport and relevant spin dynamics are illustrated with numerical examples and compared with the adiabatic transport with constant spin-orbit-coupling strength and velocity. Moreover, the influence of nonlinearity induced by interatomic interaction is discussed in terms of the Gross-Pitaevskii approach, showing the robustness of the proposed protocols. With the state-of-the-art experiments, such an inverse engineering technique paves the way for coherent control of spin-orbit-coupled Bose-Einstein condensates in harmonic traps.

Spin Wave Theory in Two-Dimensional Coupled Antiferromagnets

Science.gov (United States)

Shimahara, Hiroshi

2018-04-01

We apply spin wave theory to two-dimensional coupled antiferromagnets. In particular, we primarily examine a system that consists of small spins coupled by a strong exchange interaction J1, large spins coupled by a weak exchange interaction J2, and an anisotropic exchange interaction J12 between the small and large spins. This system is an effective model of the organic antiferromagnet λ-(BETS)2FeCl4 in its insulating phase, in which intriguing magnetic phenomena have been observed, where the small and large spins correspond to π electrons and 3d spins, respectively. BETS stands for bis(ethylenedithio)tetraselenafulvalene. We obtain the antiferromagnetic transition temperature TN and the sublattice magnetizations m(T) and M(T) of the small and large spins, respectively, as functions of the temperature T. When T increases, m(T) is constant with a slight decrease below TN, even where M(T) decreases significantly. When J1 ≫ J12 and J2 = 0, an analytical expression for TN is derived. The estimated value of TN and the behaviors of m(T) and M(T) agree with the observations of λ-(BETS)2FeCl4.

Numerical simulation of spin-qubit operation in coupled quantum dots

International Nuclear Information System (INIS)

Goto, Daisuke; Eto, Mikio

2007-01-01

Electronic states and spin operation in coupled quantum dots are numerically studied, considering realistic shape of quantum dots and electron-electron interaction. (i) We evaluate the spin coupling J between two electron spins, as a function of magnetic field perpendicular to the quantum dots. We observe a transition from antiferromagnetic coupling (J>0) to ferromagnetic coupling (J<0) at magnetic field of a few Tesla. The spin coupling is hardly influenced by the size difference between the quantum dots if the energy levels are matched. (ii) We simulate SWAP gate operations by calculating the time development of two electron spins. We show that a sudden change of tunnel barrier may result in the gate errors. The spin exchange is incomplete in the presence of strong spin-orbit interaction in InGaAs. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Spin-Orbit Coupled Bose-Einstein Condensates

Science.gov (United States)

2016-11-03

21. "Many-body physics of spin-orbit-coupled quantum gases ," Invited talk at the March Meeting 2014 in Denver, Colorado (March, 2014) 22... properties of the fundamentally new class of coherent states of quantum matter that had been predicted by the PI and subsequently experimentally...Report Title This ARO research proposal entitled "SPIN-ORBIT COUPLED BOSE-EINSTEIN CONDENSATES" (SOBECs) explored properties of the fundamentally new

Spin Pumping in Electrodynamically Coupled Magnon-Photon Systems.

Science.gov (United States)

Bai, Lihui; Harder, M; Chen, Y P; Fan, X; Xiao, J Q; Hu, C-M

2015-06-05

We use electrical detection, in combination with microwave transmission, to investigate both resonant and nonresonant magnon-photon coupling at room temperature. Spin pumping in a dynamically coupled magnon-photon system is found to be distinctly different from previous experiments. Characteristic coupling features such as modes anticrossing, linewidth evolution, peculiar line shape, and resonance broadening are systematically measured and consistently analyzed by a theoretical model set on the foundation of classical electrodynamic coupling. Our experimental and theoretical approach paves the way for pursuing microwave coherent manipulation of pure spin current via the combination of spin pumping and magnon-photon coupling.

First example of a high-level correlated calculation of the indirect spin-spin coupling constants involving tellurium

DEFF Research Database (Denmark)

Rusakov, Yury Yu; Krivdin, Leonid B.; Østerstrøm, Freja From

2013-01-01

This paper documents a very first example of a high-level correlated calculation of spin-spin coupling constants involving tellurium taking into account relativistic effects, vibrational corrections and solvent effects for the medium sized organotellurium molecules. The 125Te-1H spin-spin coupling...... constants of tellurophene and divinyl telluride were calculated at the SOPPA and DFT levels in a good agreement with experiment. A new full-electron basis set av3z-J for tellurium derived from the "relativistic" Dyall's basis set, dyall.av3z, and specifically optimized for the correlated calculations...... of spin-spin coupling constants involving tellurium, was developed. The SOPPA methods show much better performance as compared to 15 those of DFT, if relativistic effects calculated within the ZORA scheme are taken into account. Vibrational and solvent corrections are next to negligible, while...

The non-linear coupled spin 2-spin 3 Cotton equation in three dimensions

Energy Technology Data Exchange (ETDEWEB)

Linander, Hampus; Nilsson, Bengt E.W. [Department of Physics, Theoretical PhysicsChalmers University of Technology, S-412 96 Göteborg (Sweden)

2016-07-05

In the context of three-dimensional conformal higher spin theory we derive, in the frame field formulation, the full non-linear spin 3 Cotton equation coupled to spin 2. This is done by solving the corresponding Chern-Simons gauge theory system of equations, that is, using F=0 to eliminate all auxiliary fields and thus expressing the Cotton equation in terms of just the spin 3 frame field and spin 2 covariant derivatives and tensors (Schouten). In this derivation we neglect the spin 4 and higher spin sectors and approximate the star product commutator by a Poisson bracket. The resulting spin 3 Cotton equation is complicated but can be related to linearized versions in the metric formulation obtained previously by other authors. The expected symmetry (spin 3 “translation”, “Lorentz” and “dilatation”) properties are verified for Cotton and other relevant tensors but some perhaps unexpected features emerge in the process, in particular in relation to the non-linear equations. We discuss the structure of this non-linear spin 3 Cotton equation but its explicit form is only presented here, in an exact but not completely refined version, in appended files obtained by computer algebra methods. Both the frame field and metric formulations are provided.

Resolved sidebands in a strain-coupled hybrid spin-oscillator system

OpenAIRE

Teissier, Jean; Barfuss, Arne; Appel, Patrick; Neu, Elke; Maletinsky, P.

2014-01-01

We report on single electronic spins coupled to the motion of mechanical resonators by a novel mechanism based on crystal strain. Our device consists of single-crystalline diamond cantilevers with embedded Nitrogen-Vacancy center spins. Using optically detected electron spin resonance, we determine the unknown spin-strain coupling constants and demonstrate that our system resides well within the resolved sideband regime. We realize coupling strengths exceeding ten MHz under mechanical driving...

Non-Abelian hydrodynamics and the flow of spin in spin-orbit coupled substances

International Nuclear Information System (INIS)

Leurs, B.W.A.; Nazario, Z.; Santiago, D.I.; Zaanen, J.

2008-01-01

Motivated by the heavy ion collision experiments there is much activity in studying the hydrodynamical properties of non-Abelian (quark-gluon) plasmas. A major question is how to deal with color currents. Although not widely appreciated, quite similar issues arise in condensed matter physics in the context of the transport of spins in the presence of spin-orbit coupling. The key insight is that the Pauli Hamiltonian governing the leading relativistic corrections in condensed matter systems can be rewritten in a language of SU(2) covariant derivatives where the role of the non-Abelian gauge fields is taken by the physical electromagnetic fields: the Pauli system can be viewed as Yang-Mills quantum-mechanics in a 'fixed frame', and it can be viewed as an 'analogous system' for non-Abelian transport in the same spirit as Volovik's identification of the He superfluids as analogies for quantum fields in curved space time. We take a similar perspective as Jackiw and coworkers in their recent study of non-Abelian hydrodynamics, twisting the interpretation into the 'fixed frame' context, to find out what this means for spin transport in condensed matter systems. We present an extension of Jackiw's scheme: non-Abelian hydrodynamical currents can be factored in a 'non-coherent' classical part, and a coherent part requiring macroscopic non-Abelian quantum entanglement. Hereby it becomes particularly manifest that non-Abelian fluid flow is a much richer affair than familiar hydrodynamics, and this permits us to classify the various spin transport phenomena in condensed matter physics in an unifying framework. The 'particle based hydrodynamics' of Jackiw et al. is recognized as the high temperature spin transport associated with semiconductor spintronics. In this context the absence of faithful hydrodynamics is well known, but in our formulation it is directly associated with the fact that the covariant conservation of non-Abelian currents turns into a disastrous non

Inverse spin Hall effect from pulsed spin current in organic semiconductors with tunable spin-orbit coupling.

Science.gov (United States)

Sun, Dali; van Schooten, Kipp J; Kavand, Marzieh; Malissa, Hans; Zhang, Chuang; Groesbeck, Matthew; Boehme, Christoph; Valy Vardeny, Z

2016-08-01

Exploration of spin currents in organic semiconductors (OSECs) induced by resonant microwave absorption in ferromagnetic substrates is appealing for potential spintronics applications. Owing to the inherently weak spin-orbit coupling (SOC) of OSECs, their inverse spin Hall effect (ISHE) response is very subtle; limited by the microwave power applicable under continuous-wave (cw) excitation. Here we introduce a novel approach for generating significant ISHE signals in OSECs using pulsed ferromagnetic resonance, where the ISHE is two to three orders of magnitude larger compared to cw excitation. This strong ISHE enables us to investigate a variety of OSECs ranging from π-conjugated polymers with strong SOC that contain intrachain platinum atoms, to weak SOC polymers, to C60 films, where the SOC is predominantly caused by the curvature of the molecule's surface. The pulsed-ISHE technique offers a robust route for efficient injection and detection schemes of spin currents at room temperature, and paves the way for spin orbitronics in plastic materials.

Antigravity: Spin-gravity coupling in action

Science.gov (United States)

Plyatsko, Roman; Fenyk, Mykola

2016-08-01

The typical motions of a spinning test particle in Schwarzschild's background which show the strong repulsive action of the highly relativistic spin-gravity coupling are considered using the exact Mathisson-Papapetrou equations. An approximated approach to choice solutions of these equations which describe motions of the particle's proper center of mass is developed.

Ultrafast spin exchange-coupling torque via photo-excited charge-transfer processes

Science.gov (United States)

Ma, X.; Fang, F.; Li, Q.; Zhu, J.; Yang, Y.; Wu, Y. Z.; Zhao, H. B.; Lüpke, G.

2015-10-01

Optical control of spin is of central importance in the research of ultrafast spintronic devices utilizing spin dynamics at short time scales. Recently developed optical approaches such as ultrafast demagnetization, spin-transfer and spin-orbit torques open new pathways to manipulate spin through its interaction with photon, orbit, charge or phonon. However, these processes are limited by either the long thermal recovery time or the low-temperature requirement. Here we experimentally demonstrate ultrafast coherent spin precession via optical charge-transfer processes in the exchange-coupled Fe/CoO system at room temperature. The efficiency of spin precession excitation is significantly higher and the recovery time of the exchange-coupling torque is much shorter than for the demagnetization procedure, which is desirable for fast switching. The exchange coupling is a key issue in spin valves and tunnelling junctions, and hence our findings will help promote the development of exchange-coupled device concepts for ultrafast coherent spin manipulation.

The Influence of the Optical Phonons on the Non-equilibrium Spin Current in the Presence of Spin-Orbit Couplings

Science.gov (United States)

Hasanirokh, K.; Phirouznia, A.; Majidi, R.

2016-02-01

The influence of the electron coupling with non-polarized optical phonons on magnetoelectric effects of a two-dimensional electron gas system has been investigated in the presence of the Rashba and Dresselhaus spin-orbit couplings. Numerical calculations have been performed in the non-equilibrium regime. In the previous studies in this field, it has been shown that the Rashba and Dresselhaus couplings cannot generate non-equilibrium spin current and the spin current vanishes identically in the absence of other relaxation mechanisms such as lattice vibrations. However, in the current study, based on a semiclassical approach, it was demonstrated that in the presence of electron-phonon coupling, the spin current and other magnetoelectric quantities have been modulated by the strength of the spin-orbit interactions.

Engineering the Eigenstates of Coupled Spin-1/2 Atoms on a Surface.

Science.gov (United States)

Yang, Kai; Bae, Yujeong; Paul, William; Natterer, Fabian D; Willke, Philip; Lado, Jose L; Ferrón, Alejandro; Choi, Taeyoung; Fernández-Rossier, Joaquín; Heinrich, Andreas J; Lutz, Christopher P

2017-12-01

Quantum spin networks having engineered geometries and interactions are eagerly pursued for quantum simulation and access to emergent quantum phenomena such as spin liquids. Spin-1/2 centers are particularly desirable, because they readily manifest coherent quantum fluctuations. Here we introduce a controllable spin-1/2 architecture consisting of titanium atoms on a magnesium oxide surface. We tailor the spin interactions by atomic-precision positioning using a scanning tunneling microscope (STM) and subsequently perform electron spin resonance on individual atoms to drive transitions into and out of quantum eigenstates of the coupled-spin system. Interactions between the atoms are mapped over a range of distances extending from highly anisotropic dipole coupling to strong exchange coupling. The local magnetic field of the magnetic STM tip serves to precisely tune the superposition states of a pair of spins. The precise control of the spin-spin interactions and ability to probe the states of the coupled-spin network by addressing individual spins will enable the exploration of quantum many-body systems based on networks of spin-1/2 atoms on surfaces.

Nuclear spin-spin coupling in a van der Waals-bonded system: xenon dimer.

Science.gov (United States)

Vaara, Juha; Hanni, Matti; Jokisaari, Jukka

2013-03-14

Nuclear spin-spin coupling over van der Waals bond has recently been observed via the frequency shift of solute protons in a solution containing optically hyperpolarized (129)Xe nuclei. We carry out a first-principles computational study of the prototypic van der Waals-bonded xenon dimer, where the spin-spin coupling between two magnetically non-equivalent isotopes, J((129)Xe - (131)Xe), is observable. We use relativistic theory at the four-component Dirac-Hartree-Fock and Dirac-density-functional theory levels using novel completeness-optimized Gaussian basis sets and choosing the functional based on a comparison with correlated ab initio methods at the nonrelativistic level. J-coupling curves are provided at different levels of theory as functions of the internuclear distance in the xenon dimer, demonstrating cross-coupling effects between relativity and electron correlation for this property. Calculations on small Xe clusters are used to estimate the importance of many-atom effects on J((129)Xe - (131)Xe). Possibilities of observing J((129)Xe - (131)Xe) in liquid xenon are critically examined, based on molecular dynamics simulation. A simplistic spherical model is set up for the xenon dimer confined in a cavity, such as in microporous materials. It is shown that the on the average shorter internuclear distance enforced by the confinement increases the magnitude of the coupling as compared to the bulk liquid case, rendering J((129)Xe - (131)Xe) in a cavity a feasible target for experimental investigation.

Giant spin rotation under quasiparticle-photoelectron conversion: Joint effect of sublattice interference and spin-orbit coupling

DEFF Research Database (Denmark)

Kuemmeth, Ferdinand; Rashba, E I

2009-01-01

Spin- and angular-resolved photoemission spectroscopy is a basic experimental tool for unveiling spin polarization of electron eigenstates in crystals. We prove, by using spin-orbit coupled graphene as a model, that photoconversion of a quasiparticle inside a crystal into a photoelectron can...... be accompanied with a dramatic change in its spin polarization, up to a total spin flip. This phenomenon is typical of quasiparticles residing away from the Brillouin-zone center and described by higher rank spinors and results in exotic patterns in the angular distribution of photoelectrons....

Generalized Rashba-Dresselhaus spin-orbit coupling for cold atoms

International Nuclear Information System (INIS)

Juzeliunas, Gediminas; Ruseckas, Julius; Dalibard, Jean

2010-01-01

We study the possibility for generating a new type of spin-orbit coupling for the center-of-mass motion of cold atoms, using laser beams that resonantly couple N atomic internal ground states to an extra state. After a general analysis of the scheme, we concentrate on the tetrapod setup (N=4) where the atomic state can be described by a three-component spinor, evolving under the action of a Rashba-Dresselhaus-type spin-orbit coupling for a spin 1 particle. We illustrate a consequence of this coupling by studying the negative refraction of atoms at a potential step and show that the amplitude of the refracted beam is significantly increased in comparison to the known case of spin 1/2 Rashba-Dresselhaus coupling. Finally, we explore a possible implementation of this tetrapod setup, using stimulated Raman couplings between Zeeman sublevels of the ground state of alkali-metal atoms.

Approximately analytical solutions of the Manning-Rosen potential with the spin-orbit coupling term and spin symmetry

International Nuclear Information System (INIS)

Wei Gaofeng; Dong Shihai

2008-01-01

In this Letter the approximately analytical bound state solutions of the Dirac equation with the Manning-Rosen potential for arbitrary spin-orbit coupling quantum number k are carried out by taking a properly approximate expansion for the spin-orbit coupling term. In the case of exact spin symmetry, the associated two-component spinor wave functions of the Dirac equation for arbitrary spin-orbit quantum number k are presented and the corresponding bound state energy equation is derived. We study briefly two special cases; the general s-wave problem and the equal scalar and vector Manning-Rosen potential

Effects of the electron-electron interaction in the spin resonance in 2D systems with Dresselhaus spin-orbit coupling

International Nuclear Information System (INIS)

Krishtopenko, S. S.

2015-01-01

The effect of the electron-electron interaction on the spin-resonance frequency in two-dimensional electron systems with Dresselhaus spin-orbit coupling is investigated. The oscillatory dependence of many-body corrections on the magnetic field is demonstrated. It is shown that the consideration of many-body interaction leads to a decrease or an increase in the spin-resonance frequency, depending on the sign of the g factor. It is found that the term cubic in quasimomentum in Dresselhaus spin-orbit coupling partially decreases exchange corrections to the spin resonance energy in a two-dimensional system

Effects of the electron-electron interaction in the spin resonance in 2D systems with Dresselhaus spin-orbit coupling

Energy Technology Data Exchange (ETDEWEB)

Krishtopenko, S. S., E-mail: sergey.krishtopenko@mail.ru [Russian Academy of Sciences, Institute for Physics of Microstructures (Russian Federation)

2015-02-15

The effect of the electron-electron interaction on the spin-resonance frequency in two-dimensional electron systems with Dresselhaus spin-orbit coupling is investigated. The oscillatory dependence of many-body corrections on the magnetic field is demonstrated. It is shown that the consideration of many-body interaction leads to a decrease or an increase in the spin-resonance frequency, depending on the sign of the g factor. It is found that the term cubic in quasimomentum in Dresselhaus spin-orbit coupling partially decreases exchange corrections to the spin resonance energy in a two-dimensional system.

Spin-orbit-induced strong coupling of a single spin to a nanomechanical resonator

DEFF Research Database (Denmark)

Pályi, András; Struck, P R; Rudner, Mark

2012-01-01

as a realization of the Jaynes-Cummings model of quantum electrodynamics in the strong-coupling regime. A quantized flexural mode of the suspended tube plays the role of the optical mode and we identify two distinct two-level subspaces, at small and large magnetic field, which can be used as qubits in this setup......We theoretically investigate the deflection-induced coupling of an electron spin to vibrational motion due to spin-orbit coupling in suspended carbon nanotube quantum dots. Our estimates indicate that, with current capabilities, a quantum dot with an odd number of electrons can serve...

The nuclear spin-orbit coupling

International Nuclear Information System (INIS)

Bell, J.S.; Skyrme, T.H.R.

1994-01-01

Analysis of the nucleon-nucleon scattering around 100 MeV has determined the spin-orbit coupling part of the two-body scattering matrix at that energy, and a reasonable extrapolation to lower energies is possible. This scattering amplitude has been used, in the spirit of Brueckner's nuclear model, to estimate the resultant single-body spin-orbit coupling for a single nucleon interacting with a large nucleus. This resultant potential has a radial dependence approximately proportional to r -1 d ρ /dr, and with a magnitude in good agreement with that required to explain the doublet splittings in nuclei and the polarization of nucleons scattered elastically off nuclei. (author). 14 refs, 2 figs

Double perovskites with strong spin-orbit coupling

Science.gov (United States)

Cook, Ashley M.

We first present theoretical analysis of powder inelastic neutron scattering experiments in Ba2FeReO6 performed by our experimental collaborators. Ba2FeReO6, a member of the double perovskite family of materials, exhibits half-metallic behavior and high Curie temperatures Tc, making it of interest for spintronics applications. To interpret the experimental data, we develop a local moment model, which incorporates the interaction of Fe spins with spin-orbital locked magnetic moments on Re, and show that it captures the experimental observations. We then develop a tight-binding model of the double perovskite Ba 2FeReO6, a room temperature ferrimagnet with correlated and spin-orbit coupled Re t2g electrons moving in the background of Fe moments stabilized by Hund's coupling. We show that for such 3d/5d double perovskites, strong correlations on the 5d-element (Re) are essential in driving a half-metallic ground state. Incorporating both strong spin-orbit coupling and the Hubbard repulsion on Re leads to a band structure consistent with ab initio calculations. The uncovered interplay of strong correlations and spin-orbit coupling lends partial support to our previous work, which used a local moment description to capture the spin wave dispersion found in neutron scattering measurements. We then adapt this tight-binding model to study {111}-grown bilayers of half-metallic double perovskites such as Sr2FeMoO6. The combination of spin-orbit coupling, inter-orbital hybridization and symmetry-allowed trigonal distortion leads to a rich phase diagram with tunable ferromagnetic order, topological C= +/-1, +/-2 Chern bands, and a C = +/-2 quantum anomalous Hall insulator regime. We have also performed theoretical analysis of inelastic neutron scattering (INS) experiments to investigate the magnetic excitations in the weakly distorted face-centered-cubic (fcc) iridate double perovskites La2ZnIrO 6 and La2MgIrO6. Models with dominant Kitaev exchange seem to most naturally

Effect of Noise on the Decoherence of a Central Electron Spin Coupled to an Antiferromagnetic Spin Bath

Directory of Open Access Journals (Sweden)

G. C. Fouokeng

2014-01-01

Full Text Available We analyze the influence of a two-state autocorrelated noise on the decoherence and on the tunneling Landau-Zener (LZ transitions during a two-level crossing of a central electron spin (CES coupled to a one dimensional anisotropic-antiferomagnetic spin, driven by a time-dependent global external magnetic field. The energy splitting of the coupled spin system is found through an approach that computes the noise-averaged frequency. At low magnetic field intensity, the decoherence (or entangled state of a coupled spin system is dominated by the noise intensity. The effects of the magnetic field pulse and the spin gap antiferromagnetic material used suggest to us that they may be used as tools for the direct observation of the tunneling splitting through the LZ transitions in the sudden limit. We found that the dynamical frequencies display basin-like behavior decay with time, with the birth of entanglement, while the LZ transition probability shows Gaussian shape.

Thermal conductivity of magnetic insulators with strong spin-orbit coupling

Science.gov (United States)

Stamokostas, Georgios; Lapas, Panteleimon; Fiete, Gregory A.

We study the influence of spin-orbit coupling on the thermal conductivity of various types of magnetic insulators. In the absence of spin-orbit coupling and orbital-degeneracy, the strong-coupling limit of Hubbard interactions at half filling can often be adequately described in terms of a pure spin Hamiltonian of the Heisenberg form. However, in the presence of spin-orbit coupling the resulting exchange interaction can become highly anisotropic. The effect of the atomic spin-orbit coupling, taken into account through the effect of magnon-phonon interactions and the magnetic order and excitations, on the lattice thermal conductivity of various insulating magnetic systems is studied. We focus on the regime of low temperatures where the dominant source of scattering is two-magnon scattering to one-phonon processes. The thermal current is calculated within the Boltzmann transport theory. We are grateful for financial support from NSF Grant DMR-0955778.

Symmetric coupling of four spin-1/2 systems

Science.gov (United States)

Suzuki, Jun; Englert, Berthold-Georg

2012-06-01

We address the non-binary coupling of identical angular momenta based upon the representation theory for the symmetric group. A correspondence is pointed out between the complete set of commuting operators and the reference-frame-free subsystems. We provide a detailed analysis of the coupling of three and four spin-1/2 systems and discuss a symmetric coupling of four spin-1/2 systems.

Spin-orbit mediated control of spin qubits

DEFF Research Database (Denmark)

Flindt, Christian; Sørensen, A.S; Flensberg, Karsten

2006-01-01

We propose to use the spin-orbit interaction as a means to control electron spins in quantum dots, enabling both single-qubit and two-qubit operations. Very fast single-qubit operations may be achieved by temporarily displacing the electrons. For two-qubit operations the coupling mechanism is bas...... on a combination of the spin-orbit coupling and the mutual long-ranged Coulomb interaction. Compared to existing schemes using the exchange coupling, the spin-orbit induced coupling is less sensitive to random electrical fluctuations in the electrodes defining the quantum dots....

Angular dependence of spin-orbit spin-transfer torques

KAUST Repository

Lee, Ki-Seung

2015-04-06

In ferromagnet/heavy-metal bilayers, an in-plane current gives rise to spin-orbit spin-transfer torque, which is usually decomposed into fieldlike and dampinglike torques. For two-dimensional free-electron and tight-binding models with Rashba spin-orbit coupling, the fieldlike torque acquires nontrivial dependence on the magnetization direction when the Rashba spin-orbit coupling becomes comparable to the exchange interaction. This nontrivial angular dependence of the fieldlike torque is related to the Fermi surface distortion, determined by the ratio of the Rashba spin-orbit coupling to the exchange interaction. On the other hand, the dampinglike torque acquires nontrivial angular dependence when the Rashba spin-orbit coupling is comparable to or stronger than the exchange interaction. It is related to the combined effects of the Fermi surface distortion and the Fermi sea contribution. The angular dependence is consistent with experimental observations and can be important to understand magnetization dynamics induced by spin-orbit spin-transfer torques.

Angular dependence of spin-orbit spin-transfer torques

KAUST Repository

Lee, Ki-Seung; Go, Dongwook; Manchon, Aurelien; Haney, Paul M.; Stiles, M. D.; Lee, Hyun-Woo; Lee, Kyung-Jin

2015-01-01

In ferromagnet/heavy-metal bilayers, an in-plane current gives rise to spin-orbit spin-transfer torque, which is usually decomposed into fieldlike and dampinglike torques. For two-dimensional free-electron and tight-binding models with Rashba spin-orbit coupling, the fieldlike torque acquires nontrivial dependence on the magnetization direction when the Rashba spin-orbit coupling becomes comparable to the exchange interaction. This nontrivial angular dependence of the fieldlike torque is related to the Fermi surface distortion, determined by the ratio of the Rashba spin-orbit coupling to the exchange interaction. On the other hand, the dampinglike torque acquires nontrivial angular dependence when the Rashba spin-orbit coupling is comparable to or stronger than the exchange interaction. It is related to the combined effects of the Fermi surface distortion and the Fermi sea contribution. The angular dependence is consistent with experimental observations and can be important to understand magnetization dynamics induced by spin-orbit spin-transfer torques.

Magnetoconductance correction in zinc-blende semiconductor nanowires with spin-orbit coupling

Science.gov (United States)

Kammermeier, Michael; Wenk, Paul; Schliemann, John; Heedt, Sebastian; Gerster, Thomas; Schäpers, Thomas

2017-12-01

We study the effects of spin-orbit coupling on the magnetoconductivity in diffusive cylindrical semiconductor nanowires. Following up on our former study on tubular semiconductor nanowires, we focus in this paper on nanowire systems where no surface accumulation layer is formed but instead the electron wave function extends over the entire cross section. We take into account the Dresselhaus spin-orbit coupling resulting from a zinc-blende lattice and the Rashba spin-orbit coupling, which is controlled by a lateral gate electrode. The spin relaxation rate due to Dresselhaus spin-orbit coupling is found to depend neither on the spin density component nor on the wire growth direction and is unaffected by the radial boundary. In contrast, the Rashba spin relaxation rate is strongly reduced for a wire radius that is smaller than the spin precession length. The derived model is fitted to the data of magnetoconductance measurements of a heavily doped back-gated InAs nanowire and transport parameters are extracted. At last, we compare our results to previous theoretical and experimental studies and discuss the occurring discrepancies.

Spin-current emission governed by nonlinear spin dynamics.

Science.gov (United States)

Tashiro, Takaharu; Matsuura, Saki; Nomura, Akiyo; Watanabe, Shun; Kang, Keehoon; Sirringhaus, Henning; Ando, Kazuya

2015-10-16

Coupling between conduction electrons and localized magnetization is responsible for a variety of phenomena in spintronic devices. This coupling enables to generate spin currents from dynamical magnetization. Due to the nonlinearity of magnetization dynamics, the spin-current emission through the dynamical spin-exchange coupling offers a route for nonlinear generation of spin currents. Here, we demonstrate spin-current emission governed by nonlinear magnetization dynamics in a metal/magnetic insulator bilayer. The spin-current emission from the magnetic insulator is probed by the inverse spin Hall effect, which demonstrates nontrivial temperature and excitation power dependences of the voltage generation. The experimental results reveal that nonlinear magnetization dynamics and enhanced spin-current emission due to magnon scatterings are triggered by decreasing temperature. This result illustrates the crucial role of the nonlinear magnon interactions in the spin-current emission driven by dynamical magnetization, or nonequilibrium magnons, from magnetic insulators.

Spin dependent disorder in a junction device with spin orbit couplings

International Nuclear Information System (INIS)

Ganguly, Sudin; Basu, Saurabh

2016-01-01

Using the multi-probe Landauer-BUttiker formula and Green's function approach, we calculate the longitudinal conductance (LC) and spin Hall conductance (SHC) numerically in a two-dimensional junction system with the Rashba and Dresselhaus spin orbit coupling (SOC) and spin dependent disorder (SDD) in presence of both random onsite and hopping disorder strengths. It has been found that when the strengths of the RSOC and DSOC are same, the SHC vanishes. Further in presence of random onsite or hopping disorder, the SHC is still zero when the strengths of the two types of SOC, that is Rashba and Dressselhaus are the same. This indicates that the cancellation of SHC is robust even in the presence of random disorder. Only with the inclusion of SDD (onsite or hopping), a non-zero SHC is found and it increases as the strength of SDD increases. The physical implication of the existence of a non-zero SHC has been explored in this work. Finally, we have compared the effect of onsite SDD and hopping SDD on both longitudinal and spin Hall conductances. (paper)

Performance of wave function and density functional methods for water hydrogen bond spin-spin coupling constants.

Science.gov (United States)

García de la Vega, J M; Omar, S; San Fabián, J

2017-04-01

Spin-spin coupling constants in water monomer and dimer have been calculated using several wave function and density functional-based methods. CCSD, MCSCF, and SOPPA wave functions methods yield similar results, specially when an additive approach is used with the MCSCF. Several functionals have been used to analyze their performance with the Jacob's ladder and a set of functionals with different HF exchange were tested. Functionals with large HF exchange appropriately predict 1 J O H , 2 J H H and 2h J O O couplings, while 1h J O H is better calculated with functionals that include a reduced fraction of HF exchange. Accurate functionals for 1 J O H and 2 J H H have been tested in a tetramer water model. The hydrogen bond effects on these intramolecular couplings are additive when they are calculated by SOPPA(CCSD) wave function and DFT methods. Graphical Abstract Evaluation of the additive effect of the hydrogen bond on spin-spin coupling constants of water using WF and DFT methods.

Vortices in spin-orbit-coupled Bose-Einstein condensates

International Nuclear Information System (INIS)

Radic, J.; Sedrakyan, T. A.; Galitski, V.; Spielman, I. B.

2011-01-01

Realistic methods to create vortices in spin-orbit-coupled Bose-Einstein condensates are discussed. It is shown that, contrary to common intuition, rotation of the trap containing a spin-orbit condensate does not lead to an equilibrium state with static vortex structures but gives rise instead to nonequilibrium behavior described by an intrinsically time-dependent Hamiltonian. We propose here the following alternative methods to induce thermodynamically stable static vortex configurations: (i) to rotate both the lasers and the anisotropic trap and (ii) to impose a synthetic Abelian field on top of synthetic spin-orbit interactions. Effective Hamiltonians for spin-orbit condensates under such perturbations are derived for most currently known realistic laser schemes that induce synthetic spin-orbit couplings. The Gross-Pitaevskii equation is solved for several experimentally relevant regimes. The new interesting effects include spatial separation of left- and right-moving spin-orbit condensates, the appearance of unusual vortex arrangements, and parity effects in vortex nucleation where the topological excitations are predicted to appear in pairs. All these phenomena are shown to be highly nonuniversal and depend strongly on a specific laser scheme and system parameters.

SOPPA and CCSD vibrational corrections to NMR indirect spin-spin coupling constants of small hydrocarbons

DEFF Research Database (Denmark)

Faber, Rasmus; Sauer, Stephan P. A.

2015-01-01

We present zero-point vibrational corrections to the indirect nuclear spin-spin coupling constants in ethyne, ethene, cyclopropene and allene. The calculations have been carried out both at the level of the second order polarization propagator approximation (SOPPA) employing a new implementation ...

Dresselhaus spin-orbit coupling induced spin-polarization and resonance-split in n-well semiconductor superlattices

International Nuclear Information System (INIS)

Ye Chengzhi; Xue Rui; Nie, Y.-H.; Liang, J.-Q.

2009-01-01

Using the transfer matrix method, we investigate the electron transmission over multiple-well semiconductor superlattices with Dresselhaus spin-orbit coupling in the potential-well regions. The superlattice structure enhances the effect of spin polarization in the transmission spectrum. The minibands of multiple-well superlattices for electrons with different spin can be completely separated at the low incident energy, leading to the 100% spin polarization in a broad energy windows, which may be an effective scheme for realizing spin filtering. Moreover, for the transmission over n-quantum-well, it is observed that the resonance peaks in the minibands split into n-folds or (n-1)-folds depending on the well-width and barrier-thickness, which is different from the case of tunneling through n-barrier structure

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.

Spin Hall and spin swapping torques in diffusive ferromagnets

KAUST Repository

Pauyac, C. O.; Chshiev, M.; Manchon, Aurelien; Nikolaev, S. A.

2017-01-01

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.

Bends in nanotubes allow electric spin control and coupling

DEFF Research Database (Denmark)

Flensberg, Karsten; Marcus, Charles Masamed

2010-01-01

We investigate combined effects of spin-orbit coupling and magnetic field in carbon nanotubes containing one or more bends along their length. We show how bends can be used to provide electrical control of confined spins, while spins confined in straight segments remain insensitive to electric...

Spin Current Noise of the Spin Seebeck Effect and Spin Pumping

Science.gov (United States)

Matsuo, M.; Ohnuma, Y.; Kato, T.; Maekawa, S.

2018-01-01

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.

Persistent Spin Current in a Hard-Wall Confining Quantum Wire with Weak Dresselhaus Spin-Orbit Coupling

Institute of Scientific and Technical Information of China (English)

FU Xi; ZHOU Guang-Hui

2009-01-01

We investigate theoretically the spin current in a quantum wire with weak Dresselhaus spin-orbit coupling connected to two normal conductors.Both the quantum wire and conductors are described by a hard-wall confining potential.Using the electron wave-functions in the quantum wire and a new definition of spin current, we have calculated the elements of linear spin current density jTs,xi and jTs,yi(I = x, y, z).We lind that the elements jTs,xx and jTs,yy have a antisymmetrical relation and the element jTs,yz has the same amount level jTs,xx and jTs,yy.We also find a net linear spin current density, which has peaks at the center of quantum wire.The net linear spin current can induce a linear electric field, which may imply a way of spin current detection.

Robustness of spin-coupling distributions for perfect quantum state transfer

International Nuclear Information System (INIS)

Zwick, Analia; Alvarez, Gonzalo A.; Stolze, Joachim; Osenda, Omar

2011-01-01

The transmission of quantum information between different parts of a quantum computer is of fundamental importance. Spin chains have been proposed as quantum channels for transferring information. Different configurations for the spin couplings were proposed in order to optimize the transfer. As imperfections in the creation of these specific spin-coupling distributions can never be completely avoided, it is important to find out which systems are optimally suited for information transfer by assessing their robustness against imperfections or disturbances. We analyze different spin coupling distributions of spin chain channels designed for perfect quantum state transfer. In particular, we study the transfer of an initial state from one end of the chain to the other end. We quantify the robustness of different coupling distributions against perturbations and we relate it to the properties of the energy eigenstates and eigenvalues. We find that the localization properties of the systems play an important role for robust quantum state transfer.

Spin relaxation in nanowires by hyperfine coupling

International Nuclear Information System (INIS)

Echeverria-Arrondo, C.; Sherman, E.Ya.

2012-01-01

Hyperfine interactions establish limits on spin dynamics and relaxation rates in ensembles of semiconductor quantum dots. It is the confinement of electrons which determines nonzero hyperfine coupling and leads to the spin relaxation. As a result, in nanowires one would expect the vanishing of this effect due to extended electron states. However, even for relatively clean wires, disorder plays a crucial role and makes electron localization sufficient to cause spin relaxation on the time scale of the order of 10 ns. (copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Spin-Lattice Coupling and Superconductivity in Fe Pnictides

Directory of Open Access Journals (Sweden)

T. Egami

2010-01-01

Full Text Available We consider strong spin-lattice and spin-phonon coupling in iron pnictides and discuss its implications on superconductivity. Strong magneto-volume effect in iron compounds has long been known as the Invar effect. Fe pnictides also exhibit this effect, reflected in particular on the dependence of the magnetic moment on the atomic volume of Fe defined by the positions of the nearest neighbor atoms. Through the phenomenological Landau theory, developed on the basis of the calculations by the density functional theory (DFT and the experimental results, we quantify the strength of the spin-lattice interaction as it relates to the Stoner criterion for the onset of magnetism. We suggest that the coupling between electrons and phonons through the spin channel may be sufficiently strong to be an important part of the superconductivity mechanism in Fe pnictides.

Non-equilibrium study of spin wave interference in systems with both Rashba and Dresselhaus (001) spin-orbit coupling

International Nuclear Information System (INIS)

Chen, Kuo-Chin; Su, Yu-Hsin; Chang, Ching-Ray; Chen, Son-Hsien

2014-01-01

We study the electron spin transport in two dimensional electron gas (2DEG) system with both Rashba and Dresselhaus (001) spin-orbital coupling (SOC). We assume spatial behavior of spin precession in the non-equilibrium transport regime, and study also quantum interference induced by non-Abelian spin-orbit gauge field. The method we adopt in this article is the non-equilibrium Green's function within a tight binding framework. We consider one ferromagnetic lead which injects spin polarized electron to a system with equal strength of Rashba and Dresselhaus (001) SOC, and we observe the persistent spin helix property. We also consider two ferromagnetic leads injecting spin polarized electrons into a pure Dresselhaus SOC system, and we observe the resultant spin wave interference pattern

The Zeeman-split superconductivity with Rashba and Dresselhaus spin-orbit coupling

Science.gov (United States)

Zhao, Jingxiang; Yan, Xu; Gu, Qiang

2017-10-01

The superconductivity with Rashba and Dressehlaus spin-orbit coupling and Zeeman effect is investigated. The energy gaps of quasi-particles are carefully calculated. It is shown that the coexistence of two spin-orbit coupling might suppress superconductivity. Moreover, the Zeeman effect favors spin-triplet Cooper pairs.

Persistent Spin Current in a Hard-Wall Confining Quantum Wire with Weak Dresselhaus Spin-Orbit Coupling

International Nuclear Information System (INIS)

Fu Xi; Zhou Guanghui

2009-01-01

We investigate theoretically the spin current in a quantum wire with weak Dresselhaus spin-orbit coupling connected to two normal conductors. Both the quantum wire and conductors are described by a hard-wall confining potential. Using the electron wave-functions in the quantum wire and a new definition of spin current, we have calculated the elements of linear spin current density j s,xi T and j s,yi T (i = x, y, z). We find that the elements j T s,xx and j T s,yy have a antisymmetrical relation and the element j T s,yz has the same amount level as j s,xx T and j s,yy T . We also find a net linear spin current density, which has peaks at the center of quantum wire. The net linear spin current can induce a linear electric field, which may imply a way of spin current detection.

The influence of further-neighbor spin-spin interaction on a ground state of 2D coupled spin-electron model in a magnetic field

Science.gov (United States)

Čenčariková, Hana; Strečka, Jozef; Gendiar, Andrej; Tomašovičová, Natália

2018-05-01

An exhaustive ground-state analysis of extended two-dimensional (2D) correlated spin-electron model consisting of the Ising spins localized on nodal lattice sites and mobile electrons delocalized over pairs of decorating sites is performed within the framework of rigorous analytical calculations. The investigated model, defined on an arbitrary 2D doubly decorated lattice, takes into account the kinetic energy of mobile electrons, the nearest-neighbor Ising coupling between the localized spins and mobile electrons, the further-neighbor Ising coupling between the localized spins and the Zeeman energy. The ground-state phase diagrams are examined for a wide range of model parameters for both ferromagnetic as well as antiferromagnetic interaction between the nodal Ising spins and non-zero value of external magnetic field. It is found that non-zero values of further-neighbor interaction leads to a formation of new quantum states as a consequence of competition between all considered interaction terms. Moreover, the new quantum states are accompanied with different magnetic features and thus, several kinds of field-driven phase transitions are observed.

Spin current through quantum-dot spin valves

International Nuclear Information System (INIS)

Wang, J; Xing, D Y

2006-01-01

We report a theoretical study of the influence of the Coulomb interaction on the equilibrium spin current in a quantum-dot spin valve, in which the quantum dot described by the Anderson impurity model is coupled to two ferromagnetic leads with noncollinear magnetizations. In the Kondo regime, electrons transmit through the quantum dot via higher-order virtual processes, in which the spin of either lead electrons or a localized electron on the quantum dot may reverse. It is found that the magnitude of the spin current decreases with increasing Coulomb interactions due to spin flip effects on the dot. However, the spatial direction of the spin current remains unchanged; it is determined only by the exchange coupling between two noncollinear magnetizations

Interplay of nonsymmorphic symmetry and spin-orbit coupling in hyperkagome spin liquids: Applications to Na4Ir3O8

Science.gov (United States)

Huang, Biao; Kim, Yong Baek; Lu, Yuan-Ming

2017-02-01

Na4Ir3O8 provides a material platform to study three-dimensional quantum spin liquids in the geometrically frustrated hyperkagome lattice of Ir4 + ions. In this work, we consider quantum spin liquids on a hyperkagome lattice for generic spin models, focusing on the effects of anisotropic spin interactions. In particular, we classify possible Z2 and U (1 ) spin liquid states, following the projective symmetry group analysis in the slave-fermion representation. There are only three distinct Z2 spin liquids, together with 2 different U (1 ) spin liquids. The nonsymmorphic space group symmetry of the hyperkagome lattice plays a vital role in simplifying the classification, forbidding "π -flux" or "staggered-flux" phases in contrast to symmorphic space groups. We further prove that both U (1 ) states and one Z2 state among all 3 are symmetry-protected gapless spin liquids, robust against any symmetry-preserving perturbations. Motivated by the "spin-freezing" behavior recently observed in Na4Ir3O8 at low temperatures, we further investigate the nearest-neighbor spin model with the dominant Heisenberg interaction subject to all possible anisotropic perturbations from spin-orbit couplings. We find that a U (1 ) spin liquid ground state with spinon Fermi surfaces is energetically favored over Z2 states. Among all spin-orbit coupling terms, we show that only the Dzyaloshinskii-Moriya interaction can induce spin anisotropy in the ground state when perturbing from the isotropic Heisenberg limit. Our work paves the way for a systematic study of quantum spin liquids in various materials with a hyperkagome crystal structure.

Restricted magnetically balanced basis applied for relativistic calculations of indirect nuclear spin-spin coupling tensors in the matrix Dirac-Kohn-Sham framework

International Nuclear Information System (INIS)

Repisky, Michal; Komorovsky, Stanislav; Malkina, Olga L.; Malkin, Vladimir G.

2009-01-01

The relativistic four-component density functional approach based on the use of restricted magnetically balanced basis (mDKS-RMB), applied recently for calculations of NMR shielding, was extended for calculations of NMR indirect nuclear spin-spin coupling constants. The unperturbed equations are solved with the use of a restricted kinetically balanced basis set for the small component while to solve the second-order coupled perturbed DKS equations a restricted magnetically balanced basis set for the small component was applied. Benchmark relativistic calculations have been carried out for the X-H and H-H spin-spin coupling constants in the XH 4 series (X = C, Si, Ge, Sn and Pb). The method provides an attractive alternative to existing approximate two-component methods with transformed Hamiltonians for relativistic calculations of spin-spin coupling constants of heavy-atom systems. In particular, no picture-change effects arise in our method for property calculations

Gate tunable spin transport in graphene with Rashba spin-orbit coupling

Science.gov (United States)

Tan, Xiao-Dong; Liao, Xiao-Ping; Sun, Litao

2016-10-01

Recently, it attracts much attention to study spin-resolved transport properties in graphene with Rashba spin-orbit coupling (RSOC). One remarkable finding is that Klein tunneling in single layer graphene (SLG) with RSOC (SLG + R for short below) behaves as in bi-layer graphene (BLG). Based on the effective Dirac theory, we reconsider this tunneling problem and derive the analytical solution for the transmission coefficients. Our result shows that Klein tunneling in SLG + R and BLG exhibits completely different behaviors. More importantly, we find two new transmission selection rules in SLG + R, i.e., the single band to single band (S → S) and the single band to multiple bands (S → M) transmission regimes, which strongly depend on the relative height among Fermi level, RSOC, and potential barrier. Interestingly, in the S → S transmission regime, only normally incident electrons have capacity to pass through the barrier, while in the S → M transmission regime the angle-dependent tunneling becomes very prominent. Using the transmission coefficients, we also derive spin-resolved conductance analytically, and conductance oscillation with the increasing barrier height and zero conductance gap are found in SLG + R. The present study offers new insights and opportunities for developing graphene-based spin devices.

The effects of Rashba spin-orbit coupling on spin-polarized transport in hexagonal graphene nano-rings and flakes

Science.gov (United States)

Laghaei, M.; Heidari Semiromi, E.

2018-03-01

Quantum transport properties and spin polarization in hexagonal graphene nanostructures with zigzag edges and different sizes were investigated in the presence of Rashba spin-orbit interaction (RSOI). The nanostructure was considered as a channel to which two semi-infinite armchair graphene nanoribbons were coupled as input and output leads. Spin transmission and spin polarization in x, y, and z directions were calculated through applying Landauer-Buttiker formalism with tight binding model and the Green's function to the system. In these quantum structures it is shown that changing the size of system, induce and control the spin polarized currents. In short, these graphene systems are typical candidates for electrical spintronic devices as spin filtering.

Degenerate quantum gases with spin-orbit coupling: a review.

Science.gov (United States)

Zhai, Hui

2015-02-01

This review focuses on recent developments in synthetic spin-orbit (SO) coupling in ultracold atomic gases. Two types of SO coupling are discussed. One is Raman process induced coupling between spin and motion along one of the spatial directions and the other is Rashba SO coupling. We emphasize their common features in both single-particle and two-body physics and the consequences of both in many-body physics. For instance, single particle ground state degeneracy leads to novel features of superfluidity and a richer phase diagram; increased low-energy density-of-state enhances interaction effects; the absence of Galilean invariance and spin-momentum locking gives rise to intriguing behaviours of superfluid critical velocity and novel quantum dynamics; and the mixing of two-body singlet and triplet states yields a novel fermion pairing structure and topological superfluids. With these examples, we show that investigating SO coupling in cold atom systems can, enrich our understanding of basic phenomena such as superfluidity, provide a good platform for simulating condensed matter states such as topological superfluids and more importantly, result in novel quantum systems such as SO coupled unitary Fermi gas and high spin quantum gases. Finally we also point out major challenges and some possible future directions.

Steps toward an all-electric spin valve using side-gated quantum point contacts with lateral spin-orbit coupling

Science.gov (United States)

Bhandari, Nikhil; Dutta, Maitreya; Charles, James; Newrock, Richard S.; Cahay, Marc; Herbert, Stephen T.

2013-03-01

Spin-based electronics or ‘spintronics’ has been a topic of interest for over two decades. Electronic devices based on the manipulation of the electron spin are believed to offer the possibility of very small, non-volatile and ultrafast devices with very low power consumption. Since the proposal of a spin-field-effect transistor (SpinFET) by Datta and Das in 1990, many attempts have been made to achieve spin injection, detection and manipulation in semiconductor materials either by incorporating ferromagnetic materials into device architectures or by using external magnetic fields. This approach has significant design complexities, partly due to the influence of stray magnetic fields on device operation. In addition, magnetic electrodes can have magneto-resistance and spurious Hall voltages that can complicate device performance. To date, there has been no successful report of a working Datta-Das SpinFET. Over the last few years we have investigated an all-electric means of manipulating spins, one that only relies on electric fields and voltages and not on ferromagnetic materials or external magnetic fields. We believe we have found a pathway toward this goal, using in-plane side-gated quantum point contacts (QPCs) that rely on lateral spin-orbit coupling to create spin polarization. In this paper we discuss several aspects of our work, beginning with our finding what we believe is nearly complete spin-polarization in InAs QPCs by purely electrical means, our theoretical work to understand the basic mechanisms leading to that situation (asymmetric lateral confinement, lateral spin-orbit coupling and a strong e-e interaction), and our recent work extending the effort to GaAs and to dual QPC systems where one QPC acts as a polarizer and the other as an analyzer. Keynote talk at the 6th International Workshop on Advanced Materials Science and Nanotechnology, 30 October-2 November 2012, Ha Long, Vietnam.

Engineering hybrid Co-picene structures with variable spin coupling

Energy Technology Data Exchange (ETDEWEB)

Zhou, Chunsheng [Hefei National Laboratory for Physical Sciences at the Microscale and Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China); Department of Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China); Shan, Huan; Li, Bin, E-mail: libin@mail.ustc.edu.cn, E-mail: adzhao@ustc.edu.cn; Zhao, Aidi, E-mail: libin@mail.ustc.edu.cn, E-mail: adzhao@ustc.edu.cn; Wang, Bing [Hefei National Laboratory for Physical Sciences at the Microscale and Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China)

2016-04-25

We report on the in situ engineering of hybrid Co-picene magnetic structures with variable spin coupling using a low-temperature scanning tunneling microscope. Single picene molecules adsorbed on Au(111) are manipulated to accommodate individual Co atoms one by one, forming stable artificial hybrid structures with magnetism introduced by the Co atoms. By monitoring the evolution of the Kondo effect at each site of Co atom, we found that the picene molecule plays an important role in tuning the spin coupling between individual Co atoms, which is confirmed by theoretical calculations based on the density-functional theory. Our findings indicate that the hybrid metal-molecule structures with variable spin coupling on surfaces can be artificially constructed in a controlled manner.

Spin foam models of Yang-Mills theory coupled to gravity

International Nuclear Information System (INIS)

Mikovic, A

2003-01-01

We construct a spin foam model of Yang-Mills theory coupled to gravity by using a discretized path integral of the BF theory with polynomial interactions and the Barrett-Crane ansatz. In the Euclidean gravity case, we obtain a vertex amplitude which is determined by a vertex operator acting on a simple spin network function. The Euclidean gravity results can be straightforwardly extended to the Lorentzian case, so that we propose a Lorentzian spin foam model of Yang-Mills theory coupled to gravity

Entangled states decoherence in coupled molecular spin clusters

Science.gov (United States)

Troiani, Filippo; Szallas, Attila; Bellini, Valerio; Affronte, Marco

2010-03-01

Localized electron spins in solid-state systems are widely investigated as potential building blocks of quantum devices and computers. While most efforts in the field have been focused on semiconductor low-dimensional structures, molecular antiferromagnets were recently recognized as alternative implementations of effective few-level spin systems. Heterometallic, Cr-based spin rings behave as effective spin-1/2 systems at low temperature and show long decoherence times [1]; besides, they can be chemically linked and magnetically coupled in a controllable fascion [2]. Here, we theoretically investigate the decoherence of the Bell states in such ring dimers, resulting from hyperfine interactions with nuclear spins. Based on a microscopic description of the molecules [3], we simulate the effect of inhomogeneous broadening, spectral diffusion and electron-nuclear entanglement on the electron-spin coherence, estimating the role of the different nuclei (and of possible chemical substitutions), as well as the effect of simple spin-echo sequences. References: [1] F. Troiani, et al., Phys. Rev. Lett. 94, 207208 (2005). [2] G. A. Timco, S: Carretta, F. Troiani et al., Nature Nanotech. 4, 173 (2009). [3] F. Troiani, V. Bellini, and M. Affronte, Phys. Rev. B 77, 054428 (2008).

On the uniqueness of minimal coupling in higher-spin gauge theory

International Nuclear Information System (INIS)

Boulanger, Nicolas; Sundell, Per; Leclercq, Serge

2008-01-01

We address the uniqueness of the minimal couplings between higher-spin fields and gravity. These couplings are cubic vertices built from gauge non-invariant connections that induce non-abelian deformations of the gauge algebra. We show that Fradkin-Vasiliev's cubic 2-s-s vertex, which contains up to 2s-2 derivatives dressed by a cosmological constant Λ, has a limit where: (i) Λ → 0; (ii) the spin-2 Weyl tensor scales non-uniformly with s; and (iii) all lower-derivative couplings are scaled away. For s = 3 the limit yields the unique non-abelian spin 2-3-3 vertex found recently by two of the authors, thereby proving the uniqueness of the corresponding FV vertex. We extend the analysis to s = 4 and a class of spin 1-s-s vertices. The non-universality of the flat limit high-lightens not only the problematic aspects of higher-spin interactions with Λ = 0 but also the strongly coupled nature of the derivative expansion of the fully nonlinear higher-spin field equations with Λ≠0, wherein the standard minimal couplings mediated via the Lorentz connection are subleading at energy scales (|Λ|) 1/2 || E || M p . Finally, combining our results with those obtained by Metsaev, we give the complete list of all the manifestly covariant cubic couplings of the form 1-s-s and 2-s-s , in Minkowski background.

The effect of spin-orbit coupling on magnetoresistance in nonmagnetic organic semiconductors

International Nuclear Information System (INIS)

Zhao Jun-Qing; Ding Meng; Zhang Tian-You; Zhang Ning-Yu; Pang Yan-Tao; Ji Yan-Ju; Chen Ying; Wang Feng-Xiang; Fu Gang

2012-01-01

We investigated the effect of spin-orbit coupling on magnetoresistance in nonmagnetic organic semiconductors. A Lorentz-type magnetoresistance is obtained from spin-orbit coupling-dependent spin precession under the condition of a space-charge-limited current. The magnetoresistance depends on the initial spin orientation of the electron with respect to the hole in electron—hole pairs, and the increasing spin-orbit coupling slows down the change in magnetoresistance with magnetic field. The field dependence, the sign and the saturation value of the magnetoresistance are composite effects of recombination and dissociation rate constants of singlet and triplet electron—hole pairs. The simulated magnetoresistance shows good consistency with the experimental results. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

Coupled intertwiner dynamics: A toy model for coupling matter to spin foam models

Science.gov (United States)

Steinhaus, Sebastian

2015-09-01

The universal coupling of matter and gravity is one of the most important features of general relativity. In quantum gravity, in particular spin foams, matter couplings have been defined in the past, yet the mutual dynamics, in particular if matter and gravity are strongly coupled, are hardly explored, which is related to the definition of both matter and gravitational degrees of freedom on the discretization. However, extracting these mutual dynamics is crucial in testing the viability of the spin foam approach and also establishing connections to other discrete approaches such as lattice gauge theories. Therefore, we introduce a simple two-dimensional toy model for Yang-Mills coupled to spin foams, namely an Ising model coupled to so-called intertwiner models defined for SU (2 )k. The two systems are coupled by choosing the Ising coupling constant to depend on spin labels of the background, as these are interpreted as the edge lengths of the discretization. We coarse grain this toy model via tensor network renormalization and uncover an interesting dynamics: the Ising phase transition temperature turns out to be sensitive to the background configurations and conversely, the Ising model can induce phase transitions in the background. Moreover, we observe a strong coupling of both systems if close to both phase transitions.

Hanle Magnetoresistance in Thin Metal Films with Strong Spin-Orbit Coupling.

Science.gov (United States)

Vélez, Saül; Golovach, Vitaly N; Bedoya-Pinto, Amilcar; Isasa, Miren; Sagasta, Edurne; Abadia, Mikel; Rogero, Celia; Hueso, Luis E; Bergeret, F Sebastian; Casanova, Fèlix

2016-01-08

We report measurements of a new type of magnetoresistance in Pt and Ta thin films. The spin accumulation created at the surfaces of the film by the spin Hall effect decreases in a magnetic field because of the Hanle effect, resulting in an increase of the electrical resistance as predicted by Dyakonov [Phys. Rev. Lett. 99, 126601 (2007)]. The angular dependence of this magnetoresistance resembles the recently discovered spin Hall magnetoresistance in Pt/Y(3)Fe(5)O(12) bilayers, although the presence of a ferromagnetic insulator is not required. We show that this Hanle magnetoresistance is an alternative simple way to quantitatively study the coupling between charge and spin currents in metals with strong spin-orbit coupling.

Spin-orbit-coupled Bose-Einstein condensates of rotating polar molecules

Science.gov (United States)

Deng, Y.; You, L.; Yi, S.

2018-05-01

An experimental proposal for realizing spin-orbit (SO) coupling of pseudospin 1 in the ground manifold 1Σ (υ =0 ) of (bosonic) bialkali polar molecules is presented. The three spin components are composed of the ground rotational state and two substates from the first excited rotational level. Using hyperfine resolved Raman processes through two select excited states resonantly coupled by a microwave, an effective coupling between the spin tensor and linear momentum is realized. The properties of Bose-Einstein condensates for such SO-coupled molecules exhibiting dipolar interactions are further explored. In addition to the SO-coupling-induced stripe structures, the singly and doubly quantized vortex phases are found to appear, implicating exciting opportunities for exploring novel quantum physics using SO-coupled rotating polar molecules with dipolar interactions.

Spin transport in nanowires

OpenAIRE

Pramanik, S.; bandyopadhyay, S.; Cahay, M.

2003-01-01

We study high-field spin transport of electrons in a quasi one-dimensional channel of a $GaAs$ gate controlled spin interferometer (SPINFET) using a semiclassical formalism (spin density matrix evolution coupled with Boltzmann transport equation). Spin dephasing (or depolarization) is predominantly caused by D'yakonov-Perel' relaxation associated with momentum dependent spin orbit coupling effects that arise due to bulk inversion asymmetry (Dresselhaus spin orbit coupling) and structural inve...

Spin-Orbit Coupling for Photons and Polaritons in Microstructures

Directory of Open Access Journals (Sweden)

V. G. Sala

2015-03-01

Full Text Available We use coupled micropillars etched out of a semiconductor microcavity to engineer a spin-orbit Hamiltonian for photons and polaritons in a microstructure. The coupling between the spin and orbital momentum arises from the polarization-dependent confinement and tunneling of photons between adjacent micropillars arranged in the form of a hexagonal photonic molecule. It results in polariton eigenstates with distinct polarization patterns, which are revealed in photoluminescence experiments in the regime of polariton condensation. Thanks to the strong polariton nonlinearities, our system provides a photonic workbench for the quantum simulation of the interplay between interactions and spin-orbit effects, particularly when extended to two-dimensional lattices.

Magneto-Spin-Orbit Graphene: Interplay between Exchange and Spin-Orbit Couplings.

Science.gov (United States)

Rybkin, Artem G; Rybkina, Anna A; Otrokov, Mikhail M; Vilkov, Oleg Yu; Klimovskikh, Ilya I; Petukhov, Anatoly E; Filianina, Maria V; Voroshnin, Vladimir Yu; Rusinov, Igor P; Ernst, Arthur; Arnau, Andrés; Chulkov, Evgueni V; Shikin, Alexander M

2018-03-14

A rich class of spintronics-relevant phenomena require implementation of robust magnetism and/or strong spin-orbit coupling (SOC) to graphene, but both properties are completely alien to it. Here, we for the first time experimentally demonstrate that a quasi-freestanding character, strong exchange splitting and giant SOC are perfectly achievable in graphene at once. Using angle- and spin-resolved photoemission spectroscopy, we show that the Dirac state in the Au-intercalated graphene on Co(0001) experiences giant splitting (up to 0.2 eV) while being by no means distorted due to interaction with the substrate. Our calculations, based on the density functional theory, reveal the splitting to stem from the combined action of the Co thin film in-plane exchange field and Au-induced Rashba SOC. Scanning tunneling microscopy data suggest that the peculiar reconstruction of the Au/Co(0001) interface is responsible for the exchange field transfer to graphene. The realization of this "magneto-spin-orbit" version of graphene opens new frontiers for both applied and fundamental studies using its unusual electronic bandstructure.

Tunnel magnetoresistance of magnetic molecules with spin-vibron coupling

Directory of Open Access Journals (Sweden)

Ahmed Kenawy

2017-05-01

Full Text Available The effect of molecular vibrations on the tunnel magnetoresistance (TMR of a magnetic tunnel junction with a single spin-anisotropic molecule interconnecting its electrodes is investigated theoretically. We demonstrate that if these vibrations couple at the same time to the charge of tunneling electrons and to the spin of the molecule, the spin anisotropy of such a molecule becomes enhanced. This has, in turn, a profound impact on the TMR of such a device showing that molecular vibrations lead to a significant change of spin-polarized transport, differing for the parallel and antiparallel magnetic configuration of the junction.

Spin-orbit coupling and electric-dipole spin resonance in a nanowire double quantum dot.

Science.gov (United States)

Liu, Zhi-Hai; Li, Rui; Hu, Xuedong; You, J Q

2018-02-02

We study the electric-dipole transitions for a single electron in a double quantum dot located in a semiconductor nanowire. Enabled by spin-orbit coupling (SOC), electric-dipole spin resonance (EDSR) for such an electron can be generated via two mechanisms: the SOC-induced intradot pseudospin states mixing and the interdot spin-flipped tunneling. The EDSR frequency and strength are determined by these mechanisms together. For both mechanisms the electric-dipole transition rates are strongly dependent on the external magnetic field. Their competition can be revealed by increasing the magnetic field and/or the interdot distance for the double dot. To clarify whether the strong SOC significantly impact the electron state coherence, we also calculate relaxations from excited levels via phonon emission. We show that spin-flip relaxations can be effectively suppressed by the phonon bottleneck effect even at relatively low magnetic fields because of the very large g-factor of strong SOC materials such as InSb.

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.

Fermionic Hubbard model with Rashba or Dresselhaus spin-orbit coupling

Science.gov (United States)

Sun, Fadi; Ye, Jinwu; Liu, Wu-Ming

2017-06-01

In this work, we investigate the possible dramatic effects of Rashba or Dresselhaus spin-orbit coupling (SOC) on the fermionic Hubbard model in a two-dimensional square lattice. In the strong coupling limit, it leads to the rotated antiferromagnetic Heisenberg model which is a new class of quantum spin model. For a special equivalent class, we identify a new spin-orbital entangled commensurate ground (Y-y) state subject to strong quantum fluctuations at T = 0. We evaluate the quantum fluctuations by the spin wave expansion up to order 1/{S}2. In some SOC parameter regimes, the Y-y state supports a massive relativistic incommensurate magnon (C-IC) with its two gap minima positions continuously tuned by the SOC parameters. The C-IC magnons dominate all the low temperature thermodynamic quantities and also lead to the separation of the peak positions between the longitudinal and the transverse spin structure factors. In the weak coupling limit, any weak repulsive interaction also leads to a weak Y-y state. There is only a crossover from the weak to the strong coupling. High temperature expansions of the specific heats in both weak and strong coupling are presented. The dramatic roles to be played by these C-IC magnons at generic SOC parameters or under various external probes are hinted at. Experimental applications to both layered noncentrosymmetric materials and cold atoms are discussed.

Correlated calculations of indirect nuclear spin-spin coupling constants using second-order polarization propagator approximations: SOPPA and SOPPA(CCSD)

DEFF Research Database (Denmark)

Enevoldsen, Thomas; Oddershede, Jens; Sauer, Stephan P. A.

1998-01-01

We present correlated calculations of the indirect nuclear spin-spin coupling constants of HD, HF, H2O, CH4, C2H2, BH, AlH, CO and N2 at the level of the second-order polarization propagator approximation (SOPPA) and the second-order polarization propagator approximation with coupled-cluster sing...

Gate-dependent spin-orbit coupling in multielectron carbon nanotubes

DEFF Research Database (Denmark)

Jespersen, Thomas Sand; Grove-Rasmussen, Kasper; Paaske, Jens

2011-01-01

Understanding how the orbital motion of electrons is coupled to the spin degree of freedom in nanoscale systems is central for applications in spin-based electronics and quantum computation. Here we demonstrate such spin–orbit coupling in a carbon-nanotube quantum dot in the general multielectron...... graphene lattice. Our findings suggest that the spin–orbit coupling is a general property of carbon-nanotube quantum dots, which should provide a unique platform for the study of spin–orbit effects and their applications....

Drones, quasi-spin or iso-spin. A comparison of many-body techniques for general spin

International Nuclear Information System (INIS)

McKenzie, B.J.; Stedman, G.E.

1976-01-01

For an effective-spin system with 2S + 1 levels there are a number of possible mappings of spin onto pseudo-fermion operators. The relative merits of three of these methods are investigated by calculating to second order the dispersion relation for coupled spin-phonon modes in crystals containing S = 1 effective spin impurities. It is found that the drone formalism quickly becomes intractable at higher spin values, as does the related quasi-spin formalism developed in contrast with the iso-spin (or Abrinkosov projection) formalism. (author)

Spin foam models of matter coupled to gravity

International Nuclear Information System (INIS)

Mikovic, A

2002-01-01

We construct a class of spin foam models describing matter coupled to gravity, such that the gravitational sector is described by the unitary irreducible representations of the appropriate symmetry group, while the matter sector is described by the finite-dimensional irreducible representations of that group. The corresponding spin foam amplitudes in the four-dimensional gravity case are expressed in terms of the spin network amplitudes for pentagrams with additional external and internal matter edges. We also give a quantum field theory formulation of the model, where the matter degrees of freedom are described by spin network fields carrying the indices from the appropriate group representation. In the non-topological Lorentzian gravity case, we argue that the matter representations should be appropriate SO(3) or SO(2) representations contained in a given Lorentz matter representation, depending on whether one wants to describe a massive or a massless matter field. The corresponding spin network amplitudes are given as multiple integrals of propagators which are matrix spherical functions

Spin Hall effect in a 2DEG in the presence of magnetic couplings

International Nuclear Information System (INIS)

Gorini, C; Schwab, P; Dzierzawa, M; Raimondi, R; Milletari, M

2009-01-01

It is now well established that the peculiar linear-in-momentum dependence of the Rashba (and of the Dresselhaus) spin-orbit coupling leads to the vanishing of the spin Hall conductivity in the bulk of a two-dimensional electron gas (2DEG). In this paper we discuss how generic magnetic couplings change this behaviour providing then a potential handle on the spin Hall effect. In particular we examine the influence of magnetic impurities and an in-plane magnetic field. We find that in both cases there is a finite spin Hall effect and we provide explicit expressions for the spin Hall conductivity. The results can be obtained by means of the quasiclassical Green function approach, that we have recently extended to spin-orbit coupled electron systems.

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.

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.

Conductance and spin polarization for a quantum wire with the competition of Rashba and Dresselhaus spin-orbit coupling

International Nuclear Information System (INIS)

Fu Xi; Chen Zeshun; Zhong Feng; Zhou Guanghui

2010-01-01

We investigate theoretically the spin transport of a quantum wire (QW) with weak Rashba and Dresselhaus spin-orbit coupling (SOC) nonadiabatically connected to two normal leads. Using scattering matrix method and Landauer-Buettiker formula within effective free-electron approximation, we have calculated spin-dependent conductances G ↑ and G ↓ , total conductance G and spin polarization P z for a hard-wall potential confined QW. It is demonstrated that, the SOCs induce the splitting of G ↑ and G ↓ and form spin polarization P z . Moreover, the conductances present quantized plateaus, the plateaus and P z show oscillation structures near the subband edges. Furthermore, with the increase of QW width a strong spin polarization (P z ∼1) gradually becomes weak, which can be used to realize a spin filter. When the two SOCs coexist, the total conductance presents an isotropy transport due to the Rashba and Dresselhaus Hamiltonians being fixed, and the alteration of two SOCs strength ratio changes the sign of spin polarization. This may provide a way of realizing the expression of unit information by tuning gate voltage.

Dynamical Negative Differential Resistance in Antiferromagnetically Coupled Few-Atom Spin Chains

Science.gov (United States)

Rolf-Pissarczyk, Steffen; Yan, Shichao; Malavolti, Luigi; Burgess, Jacob A. J.; McMurtrie, Gregory; Loth, Sebastian

2017-11-01

We present the appearance of negative differential resistance (NDR) in spin-dependent electron transport through a few-atom spin chain. A chain of three antiferromagnetically coupled Fe atoms (Fe trimer) was positioned on a Cu2 N /Cu (100 ) surface and contacted with the spin-polarized tip of a scanning tunneling microscope, thus coupling the Fe trimer to one nonmagnetic and one magnetic lead. Pronounced NDR appears at the low bias of 7 mV, where inelastic electron tunneling dynamically locks the atomic spin in a long-lived excited state. This causes a rapid increase of the magnetoresistance between the spin-polarized tip and Fe trimer and quenches elastic tunneling. By varying the coupling strength between the tip and Fe trimer, we find that in this transport regime the dynamic locking of the Fe trimer competes with magnetic exchange interaction, which statically forces the Fe trimer into its high-magnetoresistance state and removes the NDR.

Ground State of Bosons in Bose-Fermi Mixture with Spin-Orbit Coupling

Science.gov (United States)

Sakamoto, Ryohei; Ono, Yosuke; Hatsuda, Rei; Shiina, Kenta; Arahata, Emiko; Mori, Hiroyuki

2017-07-01

We study an effect of spin-1/2 fermions on the ground state of a Bose system with equal Rashba and Dresselhaus spin-orbit coupling. By using mean-field and tight-binding approximations, we show the ground state phase diagram of the Bose system in the spin-orbit coupled Bose-Fermi mixture and find that the characteristic phase domain, where a spin current of fermions may be induced, can exist even in the presence of a significantly large number of fermions.

Nuclear spin noise in the central spin model

Science.gov (United States)

Fröhling, Nina; Anders, Frithjof B.; Glazov, Mikhail

2018-05-01

We study theoretically the fluctuations of the nuclear spins in quantum dots employing the central spin model which accounts for the hyperfine interaction of the nuclei with the electron spin. These fluctuations are calculated both with an analytical approach using homogeneous hyperfine couplings (box model) and with a numerical simulation using a distribution of hyperfine coupling constants. The approaches are in good agreement. The box model serves as a benchmark with low computational cost that explains the basic features of the nuclear spin noise well. We also demonstrate that the nuclear spin noise spectra comprise a two-peak structure centered at the nuclear Zeeman frequency in high magnetic fields with the shape of the spectrum controlled by the distribution of the hyperfine constants. This allows for direct access to this distribution function through nuclear spin noise spectroscopy.

Computational quantum chemistry for single Heisenberg spin couplings made simple: Just one spin flip required

International Nuclear Information System (INIS)

Mayhall, Nicholas J.; Head-Gordon, Martin

2014-01-01

We highlight a simple strategy for computing the magnetic coupling constants, J, for a complex containing two multiradical centers. On the assumption that the system follows Heisenberg Hamiltonian physics, J is obtained from a spin-flip electronic structure calculation where only a single electron is excited (and spin-flipped), from the single reference with maximum S ^ z , M, to the M − 1 manifold, regardless of the number of unpaired electrons, 2M, on the radical centers. In an active space picture involving 2M orbitals, only one β electron is required, together with only one α hole. While this observation is extremely simple, the reduction in the number of essential configurations from exponential in M to only linear provides dramatic computational benefits. This (M, M − 1) strategy for evaluating J is an unambiguous, spin-pure, wave function theory counterpart of the various projected broken symmetry density functional theory schemes, and likewise gives explicit energies for each possible spin-state that enable evaluation of properties. The approach is illustrated on five complexes with varying numbers of unpaired electrons, for which one spin-flip calculations are used to compute J. Some implications for further development of spin-flip methods are discussed

Room-temperature coupling between electrical current and nuclear spins in OLEDs

Science.gov (United States)

Malissa, H.; Kavand, M.; Waters, D. P.; van Schooten, K. J.; Burn, P. L.; Vardeny, Z. V.; Saam, B.; Lupton, J. M.; Boehme, C.

2014-09-01

The effects of external magnetic fields on the electrical conductivity of organic semiconductors have been attributed to hyperfine coupling of the spins of the charge carriers and hydrogen nuclei. We studied this coupling directly by implementation of pulsed electrically detected nuclear magnetic resonance spectroscopy in organic light-emitting diodes (OLEDs). The data revealed a fingerprint of the isotope (protium or deuterium) involved in the coherent spin precession observed in spin-echo envelope modulation. Furthermore, resonant control of the electric current by nuclear spin orientation was achieved with radiofrequency pulses in a double-resonance scheme, implying current control on energy scales one-millionth the magnitude of the thermal energy.

Computations of the chirality-sensitive effect induced by an antisymmetric indirect spin–spin coupling

Science.gov (United States)

Garbacz, Piotr

2018-05-01

Results of quantum mechanical computations of the antisymmetric part of the indirect spin-spin coupling tensor, ?, performed using the coupled-cluster method, the second-order polarisation propagator approximation, and the density functional theory for 25 molecules and nearly 100 spin-spin couplings are reported. These results are used for an estimation of the magnitude of the recently proposed liquid-state nuclear magnetic resonance chirality-sensitive effect, which allows to determine the molecular chirality directly, i.e. without the need for the application of any chiral agent. The following were found: (i) the antisymmetry J⋆ is usually larger for the coupling between spins separated by two chemical bonds in comparison with the coupling through one bond, (ii) promising samples are those which contain fluorine, and (iii) the antisymmetry of the spin-spin coupling tensor is of the order of a few hertz for commercially available chemical compounds. Therefore, the relevant property of the experiment, the pseudoscalar Jc, for them is of the order of 1 nHz m/V.

Tuning the effective spin-orbit coupling in molecular semiconductors

KAUST Repository

Schott, Sam

2017-05-11

The control of spins and spin to charge conversion in organics requires understanding the molecular spin-orbit coupling (SOC), and a means to tune its strength. However, quantifying SOC strengths indirectly through spin relaxation effects has proven difficult due to competing relaxation mechanisms. Here we present a systematic study of the g-tensor shift in molecular semiconductors and link it directly to the SOC strength in a series of high-mobility molecular semiconductors with strong potential for future devices. The results demonstrate a rich variability of the molecular g-shifts with the effective SOC, depending on subtle aspects of molecular composition and structure. We correlate the above g-shifts to spin-lattice relaxation times over four orders of magnitude, from 200 to 0.15 μs, for isolated molecules in solution and relate our findings for isolated molecules in solution to the spin relaxation mechanisms that are likely to be relevant in solid state systems.

Tuning the effective spin-orbit coupling in molecular semiconductors

KAUST Repository

Schott, Sam; McNellis, Erik R.; Nielsen, Christian B.; Chen, Hung-Yang; Watanabe, Shun; Tanaka, Hisaaki; McCulloch, Iain; Takimiya, Kazuo; Sinova, Jairo; Sirringhaus, Henning

2017-01-01

The control of spins and spin to charge conversion in organics requires understanding the molecular spin-orbit coupling (SOC), and a means to tune its strength. However, quantifying SOC strengths indirectly through spin relaxation effects has proven difficult due to competing relaxation mechanisms. Here we present a systematic study of the g-tensor shift in molecular semiconductors and link it directly to the SOC strength in a series of high-mobility molecular semiconductors with strong potential for future devices. The results demonstrate a rich variability of the molecular g-shifts with the effective SOC, depending on subtle aspects of molecular composition and structure. We correlate the above g-shifts to spin-lattice relaxation times over four orders of magnitude, from 200 to 0.15 μs, for isolated molecules in solution and relate our findings for isolated molecules in solution to the spin relaxation mechanisms that are likely to be relevant in solid state systems.

Quasiclassical methods for spin-charge coupled dynamics in low-dimensional systems

International Nuclear Information System (INIS)

Corini, Cosimo

2009-01-01

Spintronics is a new field of study whose broad aim is the manipulation of the spin degrees of freedom in solid state systems. One of its main goals is the realization of devices capable of exploiting, besides the charge, the carriers' - and possibly the nuclei's - spin. The presence of spin-orbit coupling in a system enables the spin and charge degrees of freedom to ''communicate'', a favorable situation if one is to realize such devices. More importantly, it offers the opportunity of doing so by relying solely on electric fields, whereas magnetic fields are otherwise required. Eminent examples of versatile systems with built-in and variously tunable spin-orbit interaction are two-dimensional electron - or hole - gases. The study of spin-charge coupled dynamics in such a context faces a large number of open questions, both of the fundamental and of the more practical type. To tackle the problem we rely on the quasiclassical formalism. This is an approximate quantum-field theoretical formulation with a solid microscopic foundation, perfectly suited for describing phenomena at the mesoscopic scale, and bearing a resemblance to standard Boltzmann theory which makes for physical transparency. Originally born to deal with transport in electron-phonon systems, we first generalize it to the case in which spin-orbit coupling is present, and then move on to apply it to specific situations and phenomena. Among these, to the description of the spin Hall effect and of voltage induced spin polarizations in two-dimensional electron gases under a variety of conditions - stationary or time-dependent, in the presence of magnetic and non-magnetic disorder, in the bulk or in confined geometries -, and to the problem of spin relaxation in narrow wires. (orig.)

Quasiclassical methods for spin-charge coupled dynamics in low-dimensional systems

Energy Technology Data Exchange (ETDEWEB)

Corini, Cosimo

2009-06-12

Spintronics is a new field of study whose broad aim is the manipulation of the spin degrees of freedom in solid state systems. One of its main goals is the realization of devices capable of exploiting, besides the charge, the carriers' - and possibly the nuclei's - spin. The presence of spin-orbit coupling in a system enables the spin and charge degrees of freedom to ''communicate'', a favorable situation if one is to realize such devices. More importantly, it offers the opportunity of doing so by relying solely on electric fields, whereas magnetic fields are otherwise required. Eminent examples of versatile systems with built-in and variously tunable spin-orbit interaction are two-dimensional electron - or hole - gases. The study of spin-charge coupled dynamics in such a context faces a large number of open questions, both of the fundamental and of the more practical type. To tackle the problem we rely on the quasiclassical formalism. This is an approximate quantum-field theoretical formulation with a solid microscopic foundation, perfectly suited for describing phenomena at the mesoscopic scale, and bearing a resemblance to standard Boltzmann theory which makes for physical transparency. Originally born to deal with transport in electron-phonon systems, we first generalize it to the case in which spin-orbit coupling is present, and then move on to apply it to specific situations and phenomena. Among these, to the description of the spin Hall effect and of voltage induced spin polarizations in two-dimensional electron gases under a variety of conditions - stationary or time-dependent, in the presence of magnetic and non-magnetic disorder, in the bulk or in confined geometries -, and to the problem of spin relaxation in narrow wires. (orig.)

Rashba and Dresselhaus spin-orbit coupling effects on tunnelling through two-dimensional magnetic quantum systems

International Nuclear Information System (INIS)

Xu Wen; Guo Yong

2005-01-01

We investigate the influence of the Rashba and Dresselhaus spin-orbit coupling interactions on tunnelling through two-dimensional magnetic quantum systems. It is showed that not only Rashba spin-orbit coupling but also Dresselhaus one can affect spin tunnelling properties greatly in such a quantum system. The transmission possibility, the spin polarization and the conductance are obviously oscillated with both coupling strengths. High spin polarization, conductance and magnetic conductance of the structure can be obtained by modulating either Rashba or Dresselhaus coupling strength

Dynamics of High-Order Spin-Orbit Couplings about Linear Momenta in Compact Binary Systems*

International Nuclear Information System (INIS)

Huang Li; Wu Xin; Huang Guo-Qing; Mei Li-Jie

2017-01-01

This paper relates to the post-Newtonian Hamiltonian dynamics of spinning compact binaries, consisting of the Newtonian Kepler problem and the leading, next-to-leading and next-to-next-to-leading order spin-orbit couplings as linear functions of spins and momenta. When this Hamiltonian form is transformed to a Lagrangian form, besides the terms corresponding to the same order terms in the Hamiltonian, several additional terms, third post-Newtonian (3PN), 4PN, 5PN, 6PN and 7PN order spin-spin coupling terms, yield in the Lagrangian. That means that the Hamiltonian is nonequivalent to the Lagrangian at the same PN order but is exactly equivalent to the full Lagrangian without any truncations. The full Lagrangian without the spin-spin couplings truncated is integrable and regular. Whereas it is non-integrable and becomes possibly chaotic when any one of the spin-spin terms is dropped. These results are also supported numerically. (paper)

Optical switching of nuclear spin-spin couplings in semiconductors.

Science.gov (United States)

Goto, Atsushi; Ohki, Shinobu; Hashi, Kenjiro; Shimizu, Tadashi

2011-07-05

Two-qubit operation is an essential part of quantum computation. However, solid-state nuclear magnetic resonance quantum computing has not been able to fully implement this functionality, because it requires a switchable inter-qubit coupling that controls the time evolutions of entanglements. Nuclear dipolar coupling is beneficial in that it is present whenever nuclear-spin qubits are close to each other, while it complicates two-qubit operation because the qubits must remain decoupled to prevent unwanted couplings. Here we introduce optically controllable internuclear coupling in semiconductors. The coupling strength can be adjusted externally through light power and even allows on/off switching. This feature provides a simple way of switching inter-qubit couplings in semiconductor-based quantum computers. In addition, its long reach compared with nuclear dipolar couplings allows a variety of options for arranging qubits, as they need not be next to each other to secure couplings.

Condensation of bosons with Rashba-Dresselhaus spin-orbit coupling

International Nuclear Information System (INIS)

Baym, Gordon; Ozawa, Tomoki

2014-01-01

Cold atomic Bose-Einstein systems in the presence of simulated Rashba- Dresselhaus spin-orbit coupling exhibit novel physical features. With pure in-plane Rashba coupling the system is predicted in Bogoliubov-Hartree-Fock to have a stable Bose condensate below a critical temperature, even though the effective density of states is two-dimensional. In addition the system has a normal state at all temperatures. We review here the new physics when the system has such spin-orbit coupling, and discuss the nature of the finite temperature condensation phase transition from the normal to condensed phases.

/sup 13/C-/sup 13/C spin-spin coupling constants in structural investigations. V. The direct carbon-carbon coupling constants in the vinyl group

Energy Technology Data Exchange (ETDEWEB)

Krivdin, L.B.; Shcherbakov, V.V.; Kalabin, G.A.

1988-03-10

The direct spin-spin coupling constants in the vinyl group were measured in 100 mono-substituted ethylene derivatives. The inductive effect of the substituent was found to be the major factor in the variation of this constant and, in some cases, the stereospecific effect of the unshared electron pairs of heteratoms makes a significant contribution to the /sup 13/C-/sup 13/C coupling constants.

Bulk electron spin polarization generated by the spin Hall current

OpenAIRE

Korenev, V. L.

2005-01-01

It is shown that the spin Hall current generates a non-equilibrium spin polarization in the interior of crystals with reduced symmetry in a way that is drastically different from the previously well-known equilibrium polarization during the spin relaxation process. The steady state spin polarization value does not depend on the strength of spin-orbit interaction offering possibility to generate relatively high spin polarization even in the case of weak spin-orbit coupling.

Bulk electron spin polarization generated by the spin Hall current

Science.gov (United States)

Korenev, V. L.

2006-07-01

It is shown that the spin Hall current generates a nonequilibrium spin polarization in the interior of crystals with reduced symmetry in a way that is drastically different from the previously well-known “equilibrium” polarization during the spin relaxation process. The steady state spin polarization value does not depend on the strength of spin-orbit interaction offering possibility to generate relatively high spin polarization even in the case of weak spin-orbit coupling.

On-chip spin-controlled orbital angular momentum directional coupling

Science.gov (United States)

Xie, Zhenwei; Lei, Ting; Si, Guangyuan; Du, Luping; Lin, Jiao; Min, Changjun; Yuan, Xiaocong

2018-01-01

Optical vortex beams have many potential applications in the particle trapping, quantum encoding, optical orbital angular momentum (OAM) communications and interconnects. However, the on-chip compact OAM detection is still a big challenge. Based on a holographic configuration and a spin-dependent structure design, we propose and demonstrate an on-chip spin-controlled OAM-mode directional coupler, which can couple the OAM signal to different directions due to its topological charge. While the directional coupling function can be switched on/off by altering the spin of incident beam. Both simulation and experimental measurements verify the validity of the proposed approach. This work would benefit the on-chip OAM devices for optical communications and high dimensional quantum coding/decoding in the future.

Macroscopic spin-orbit coupling in non-uniform magnetic fields

Energy Technology Data Exchange (ETDEWEB)

Tabat, N.; Edelman, H. S.; Song, D. [Semaphore Scientific, Inc., St. Cloud, Minnesota 56301 (United States); Vogt, T. [Department of Electrical and Computer Engineering, St. Cloud State University, St. Cloud, Minnesota 56301 (United States)

2015-03-02

Translational dynamics of aggregated magnetic nano-particles placed in a rotating external magnetic field is described. It is observed and explained that aggregates that spin within a radially decreasing field strength must execute an orbital motion of their center of mass in a sense that counters their spin rotation. This orbital motion is tightly coupled to the spin dynamics of the aggregates. An analytical model for the canonical variables describing the orbital motion is derived and shown to be in good agreement with the measured values.

Macroscopic spin-orbit coupling in non-uniform magnetic fields

International Nuclear Information System (INIS)

Tabat, N.; Edelman, H. S.; Song, D.; Vogt, T.

2015-01-01

Translational dynamics of aggregated magnetic nano-particles placed in a rotating external magnetic field is described. It is observed and explained that aggregates that spin within a radially decreasing field strength must execute an orbital motion of their center of mass in a sense that counters their spin rotation. This orbital motion is tightly coupled to the spin dynamics of the aggregates. An analytical model for the canonical variables describing the orbital motion is derived and shown to be in good agreement with the measured values

Spin-charge coupled dynamics driven by a time-dependent magnetization

Science.gov (United States)

Tölle, Sebastian; Eckern, Ulrich; Gorini, Cosimo

2017-03-01

The spin-charge coupled dynamics in a thin, magnetized metallic system are investigated. The effective driving force acting on the charge carriers is generated by a dynamical magnetic texture, which can be induced, e.g., by a magnetic material in contact with a normal-metal system. We consider a general inversion-asymmetric substrate/normal-metal/magnet structure, which, by specifying the precise nature of each layer, can mimic various experimentally employed setups. Inversion symmetry breaking gives rise to an effective Rashba spin-orbit interaction. We derive general spin-charge kinetic equations which show that such spin-orbit interaction, together with anisotropic Elliott-Yafet spin relaxation, yields significant corrections to the magnetization-induced dynamics. In particular, we present a consistent treatment of the spin density and spin current contributions to the equations of motion, inter alia, identifying a term in the effective force which appears due to a spin current polarized parallel to the magnetization. This "inverse-spin-filter" contribution depends markedly on the parameter which describes the anisotropy in spin relaxation. To further highlight the physical meaning of the different contributions, the spin-pumping configuration of typical experimental setups is analyzed in detail. In the two-dimensional limit the buildup of dc voltage is dominated by the spin-galvanic (inverse Edelstein) effect. A measuring scheme that could isolate this contribution is discussed.

Density of states and phase diagram of the antiferromagnetic spin chain with Dzyaloshinsky-Moriya interaction and spin-phonon coupling

International Nuclear Information System (INIS)

Wang Qin; Chen Hong; Zheng Hang

2007-01-01

The effects of DM interaction on the density-of-states, the dimerization and the phase diagram in the antiferromagnetic Heisenberg chain coupled with quantum phonons have been studied by a nonadiabatic analytical approach. The results show that the effect of the DM interaction is to increase the staggered antisymmetric spin exchange interaction order but to decrease the spin dimerization and their competitions result in the lattice dimerization ordering parameter to increase for large staggered DM interaction parameter β and decrease for small β. A crossover of β exists in which the dimerization ordering parameter changes non-monotonously. As the DM interaction parameter D increases, depending on the appropriate values of spin-phonon coupling, phonon frequency and β, the system undergoes phase transition from spin gapless state to gapped state or reversely and can even reenter between the two states. The relation between the phonon-staggered ordering parameter, the spin-dimer order parameter and the staggered DM interaction order parameter gives clearly their contributing weights to the lattice dimerization

Development of New Open-Shell Perturbation and Coupled-Cluster Theories Based on Symmetric Spin Orbitals

Science.gov (United States)

Lee, Timothy J.; Arnold, James O. (Technical Monitor)

1994-01-01

A new spin orbital basis is employed in the development of efficient open-shell coupled-cluster and perturbation theories that are based on a restricted Hartree-Fock (RHF) reference function. The spin orbital basis differs from the standard one in the spin functions that are associated with the singly occupied spatial orbital. The occupied orbital (in the spin orbital basis) is assigned the delta(+) = 1/square root of 2(alpha+Beta) spin function while the unoccupied orbital is assigned the delta(-) = 1/square root of 2(alpha-Beta) spin function. The doubly occupied and unoccupied orbitals (in the reference function) are assigned the standard alpha and Beta spin functions. The coupled-cluster and perturbation theory wave functions based on this set of "symmetric spin orbitals" exhibit much more symmetry than those based on the standard spin orbital basis. This, together with interacting space arguments, leads to a dramatic reduction in the computational cost for both coupled-cluster and perturbation theory. Additionally, perturbation theory based on "symmetric spin orbitals" obeys Brillouin's theorem provided that spin and spatial excitations are both considered. Other properties of the coupled-cluster and perturbation theory wave functions and models will be discussed.

/sup 13/C-/sup 13/C spin-spin coupling constants in structural investigations. I. New method of determining the configuration of oximes and their derivatives

Energy Technology Data Exchange (ETDEWEB)

Krivdin, L.B.; Shcherbakov, V.V.; Kalabin, G.A.

1986-07-10

It was shown that the direct /sup 13/C-/sup 13/C spin-spin coupling constants can be used for the unambiguous identification of the configurational isomers of oximes and their derivatives. The stereospecificity of the constants is explained by the additional contribution from the unshared electron pair of the nitrogen atom to the spin-spin coupling constant between the adjacent carbon nuclei in the cis position.

Measure synchronization in a spin-orbit-coupled bosonic Josephson junction

Science.gov (United States)

Wang, Wen-Yuan; Liu, Jie; Fu, Li-Bin

2015-11-01

We present measure synchronization (MS) in a bosonic Josephson junction with spin-orbit coupling. The two atomic hyperfine states are coupled by a Raman dressing scheme, and they are regarded as two orientations of a pseudo-spin-1 /2 system. A feature specific to a spin-orbit-coupled (SOC) bosonic Josephson junction is that the transition from non-MS to MS dynamics can be modulated by Raman laser intensity, even in the absence of interspin atomic interaction. A phase diagram of non-MS and MS dynamics as functions of Raman laser intensity and Josephson tunneling amplitude is presented. Taking into account interspin atomic interactions, the system exhibits MS breaking dynamics resulting from the competition between intraspin and interspin atomic interactions. When interspin atomic interactions dominate in the competition, the system always exhibits MS dynamics. For interspin interaction weaker than intraspin interaction, a window for non-MS dynamics is present. Since SOC Bose-Einstein condensates provide a powerful platform for studies on physical problems in various fields, the study of MS dynamics is valuable in researching the collective coherent dynamical behavior in a spin-orbit-coupled bosonic Josephson junction.

Depolarization of the electron spin in storage rings by nonlinear spin-orbit coupling

International Nuclear Information System (INIS)

Kewisch, J.

1985-10-01

Electrons and positrons which circulate in the storage ring are polarized at the emission of synchrotron radiation by the so called Sokolov-Ternov effect. This polarization is on the one hand of large interest for the study of the weak interaction, on the other hand it can be used for the accurate measurement of the beam energy and by this of the mass of elementary particles. The transverse and longitudinal particle vibrations simultaneously excited by the synchrotron radiation however can effect that this polarization is destroyed. This effect is called spin-orbit coupling. For the calculation of the spin-orbit coupling the computer program SITROS was written. This program is a tracking program: The motion of some sample particles and their spin vectors are calculated for some thousand circulations. From this the mean depolarization and by extrapolation the degree of polarization of the equilibrium state is determined. Contrarily to the known program SLIM which is based on perturbational calculations in SITROS the nonlinear forces in the storage ring can be regarded. By this the calculation of depolarizing higher order resonances is made possible. In this thesis the equations of motion for the orbital and spin motion of the electrons are derived which form the base for the program SITROS. The functions of the program and the approximations necessary for the saving of calculational time are explained. The comparison of the SITROS results with the measurement results obtained at the PETRA storage ring shows that the SITROS program is a useful means for the planning and calculation of storage rings with polarized electron beams. (orig.) [de

Spin precession and spin waves in a chiral electron gas: Beyond Larmor's theorem

Science.gov (United States)

Karimi, Shahrzad; Baboux, Florent; Perez, Florent; Ullrich, Carsten A.; Karczewski, Grzegorz; Wojtowicz, Tomasz

2017-07-01

Larmor's theorem holds for magnetic systems that are invariant under spin rotation. In the presence of spin-orbit coupling this invariance is lost and Larmor's theorem is broken: for systems of interacting electrons, this gives rise to a subtle interplay between the spin-orbit coupling acting on individual single-particle states and Coulomb many-body effects. We consider a quasi-two-dimensional, partially spin-polarized electron gas in a semiconductor quantum well in the presence of Rashba and Dresselhaus spin-orbit coupling. Using a linear-response approach based on time-dependent density-functional theory, we calculate the dispersions of spin-flip waves. We obtain analytic results for small wave vectors and up to second order in the Rashba and Dresselhaus coupling strengths α and β . Comparison with experimental data from inelastic light scattering allows us to extract α and β as well as the spin-wave stiffness very accurately. We find significant deviations from the local density approximation for spin-dependent electron systems.

Non-Hermitian spin chains with inhomogeneous coupling

Energy Technology Data Exchange (ETDEWEB)

Bytsko, Andrei G. [Rossijskaya Akademiya Nauk, St. Petersburg (Russian Federation). Inst. Matematiki; Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany). Gruppe Theorie

2009-11-15

An open U{sub q}(sl{sub 2})-invariant spin chain of spin S and length N with inhomogeneous coupling is investigated as an example of a non-Hermitian (quasi-Hermitian) model. For several particular cases of such a chain, the ranges of the deformation parameter {gamma} are determined for which the spectrum of the model is real. For a certain range of {gamma}, a universal metric operator is constructed and thus the quasi-Hermiticity of the model is established. The constructed metric operator is non-dynamical, its structure is determined only by the symmetry of the model. The results apply, in particular, to all known homogeneous U{sub q}(sl{sub 2})-invariant integrable spin chains with nearest-neighbour interaction. In addition, the most general form of a metric operator for a quasi-Hermitian operator in finite dimensional space is discussed. (orig.)

Effect of asymmetric interface on charge and spin transport across two dimensional electron gas with Dresselhaus spin-orbit coupling/ferromagnet junction

Science.gov (United States)

Srisongmuang, B.; Pasanai, K.

2018-04-01

We theoretically studied the effect of interfacial scattering on the transport of charge and spin across the junction of a two-dimensional electron gas with Dresselhaus spin-orbit coupling and ferromagnetic material junction, via the conductance (G) and the spin-polarization of the conductance spectra (P) using the scattering method. At the interface, not only were the effects of spin-conserving (Z0) and spin-flip scattering (Zf) considered, but also the interfacial Rashba spin-orbit coupling scattering (ZRSOC) , which was caused by the asymmetry of the interface, was taken into account, and all of them were modeled by the delta potential. It was found that G was suppressed with increasing Z0 , as expected. Interestingly, a particular value of Zf can cause G and P to reach a maximum value. In particular, ZRSOC plays a crucial role to reduce G and P in the metallic limit, but its influence on the tunneling limit was quite weak. On the other hand, the effect of ZRSOC was diminished in the tunneling limit of the magnetic junction.

Current induced torques and interfacial spin-orbit coupling: Semiclassical modeling

KAUST Repository

Haney, Paul M.

2013-05-07

In bilayer nanowires consisting of a ferromagnetic layer and a nonmagnetic layer with strong spin-orbit coupling, currents create torques on the magnetization beyond those found in simple ferromagnetic nanowires. The resulting magnetic dynamics appear to require torques that can be separated into two terms, dampinglike and fieldlike. The dampinglike torque is typically derived from models describing the bulk spin Hall effect and the spin transfer torque, and the fieldlike torque is typically derived from a Rashba model describing interfacial spin-orbit coupling. We derive a model based on the Boltzmann equation that unifies these approaches. We also consider an approximation to the Boltzmann equation, the drift-diffusion model, that qualitatively reproduces the behavior, but quantitatively differs in some regimes. We show that the Boltzmann equation with physically reasonable parameters can match the torques for any particular sample, but in some cases, it fails to describe the experimentally observed thickness dependencies.

Coupling spin qubits via superconductors

DEFF Research Database (Denmark)

Leijnse, Martin; Flensberg, Karsten

2013-01-01

We show how superconductors can be used to couple, initialize, and read out spatially separated spin qubits. When two single-electron quantum dots are tunnel coupled to the same superconductor, the singlet component of the two-electron state partially leaks into the superconductor via crossed...... Andreev reflection. This induces a gate-controlled singlet-triplet splitting which, with an appropriate superconductor geometry, remains large for dot separations within the superconducting coherence length. Furthermore, we show that when two double-dot singlet-triplet qubits are tunnel coupled...... to a superconductor with finite charging energy, crossed Andreev reflection enables a strong two-qubit coupling over distances much larger than the coherence length....

SU (N ) spin-wave theory: Application to spin-orbital Mott insulators

Science.gov (United States)

Dong, Zhao-Yang; Wang, Wei; Li, Jian-Xin

2018-05-01

We present the application of the SU (N ) spin-wave theory to spin-orbital Mott insulators whose ground states exhibit magnetic orders. When taking both spin and orbital degrees of freedom into account rather than projecting Hilbert space onto the Kramers doublet, which is the lowest spin-orbital locked energy levels, the SU (N ) spin-wave theory should take the place of the SU (2 ) one due to the inevitable spin-orbital multipole exchange interactions. To implement the application, we introduce an efficient general local mean-field method, which involves all local fluctuations, and develop the SU (N ) linear spin-wave theory. Our approach is tested firstly by calculating the multipolar spin-wave spectra of the SU (4 ) antiferromagnetic model. Then, we apply it to spin-orbital Mott insulators. It is revealed that the Hund's coupling would influence the effectiveness of the isospin-1 /2 picture when the spin-orbital coupling is not large enough. We further carry out the SU (N ) spin-wave calculations of two materials, α -RuCl3 and Sr2IrO4 , and find that the magnonic and spin-orbital excitations are consistent with experiments.

Electron spin and nuclear spin manipulation in semiconductor nanosystems

International Nuclear Information System (INIS)

Hirayama, Yoshiro; Yusa, Go; Sasaki, Satoshi

2006-01-01

Manipulations of electron spin and nuclear spin have been studied in AlGaAs/GaAs semiconductor nanosystems. Non-local manipulation of electron spins has been realized by using the correlation effect between localized and mobile electron spins in a quantum dot- quantum wire coupled system. Interaction between electron and nuclear spins was exploited to achieve a coherent control of nuclear spins in a semiconductor point contact device. Using this device, we have demonstrated a fully coherent manipulation of any two states among the four spin levels of Ga and As nuclei. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Coupled-spin filtered MR imaging in a low field

International Nuclear Information System (INIS)

Baudouin, C.J.; Bryant, D.J.; Coutts, G.A.; Bydder, G.M.; Young, I.R.

1990-01-01

This paper investigates the use of an editing method of imaging using spin-echo sequences with differing radio-frequency (RF) pulses for lipid imaging in poor fields and to compare it with solvent-suppression methods. A technique of echo difference imaging (EDI) has been described in which two data sets are acquired: a normal spin-echo sequence (90-180) and a 90-90 spin-echo sequence. The intrinsic signal of uncoupled spins in the EDI method is one-half that of the conventional sequence, so that subtracting twice the EDI signal from the conventional signal should result in signal cancellation. With coupled spins, the application of the second 90 degrees pulse results in coherence transfer, and echo magnitude will not be one-half that of the 90-180 echo. This method of lipid imaging may be less vulnerable to field inhomogeneity than are solvent-suppression methods. Phantom and in vivo studies were performed at 0.15 T (TE = 44 msec and various TRs)

Spin symmetry in the relativistic symmetrical well potential including a proper approximation to the spin-orbit coupling term

International Nuclear Information System (INIS)

Wei Gaofeng; Dong Shihai

2010-01-01

In the case of exact spin symmetry, we approximately solve the Dirac equation with scalar and vector symmetrical well potentials by using a proper approximation to the spin-orbit coupling term, and obtain the corresponding energy equation and spinor wave functions for the bound states. We find that there exist only positive-energy bound states in the case of spin symmetry. Also, the energy eigenvalue approaches a constant when the potential parameter α goes to zero. The special case for equally scalar and vector symmetrical well potentials is studied briefly.

Relativistic four-component calculations of indirect nuclear spin-spin couplings with efficient evaluation of the exchange-correlation response kernel

Energy Technology Data Exchange (ETDEWEB)

Křístková, Anežka; Malkin, Vladimir G. [Institute of Inorganic Chemistry, Slovak Academy of Sciences, Dúbravská cesta 9, SK-84536 Bratislava (Slovakia); Komorovsky, Stanislav; Repisky, Michal [Centre for Theoretical and Computational Chemistry, University of Tromsø - The Arctic University of Norway, N-9037 Tromsø (Norway); Malkina, Olga L., E-mail: olga.malkin@savba.sk [Institute of Inorganic Chemistry, Slovak Academy of Sciences, Dúbravská cesta 9, SK-84536 Bratislava (Slovakia); Department of Inorganic Chemistry, Comenius University, Bratislava (Slovakia)

2015-03-21

In this work, we report on the development and implementation of a new scheme for efficient calculation of indirect nuclear spin-spin couplings in the framework of four-component matrix Dirac-Kohn-Sham approach termed matrix Dirac-Kohn-Sham restricted magnetic balance resolution of identity for J and K, which takes advantage of the previous restricted magnetic balance formalism and the density fitting approach for the rapid evaluation of density functional theory exchange-correlation response kernels. The new approach is aimed to speedup the bottleneck in the solution of the coupled perturbed equations: evaluation of the matrix elements of the kernel of the exchange-correlation potential. The performance of the new scheme has been tested on a representative set of indirect nuclear spin-spin couplings. The obtained results have been compared with the corresponding results of the reference method with traditional evaluation of the exchange-correlation kernel, i.e., without employing the fitted electron densities. Overall good agreement between both methods was observed, though the new approach tends to give values by about 4%-5% higher than the reference method. On the average, the solution of the coupled perturbed equations with the new scheme is about 8.5 times faster compared to the reference method.

Relativistic four-component calculations of indirect nuclear spin-spin couplings with efficient evaluation of the exchange-correlation response kernel

International Nuclear Information System (INIS)

Křístková, Anežka; Malkin, Vladimir G.; Komorovsky, Stanislav; Repisky, Michal; Malkina, Olga L.

2015-01-01

In this work, we report on the development and implementation of a new scheme for efficient calculation of indirect nuclear spin-spin couplings in the framework of four-component matrix Dirac-Kohn-Sham approach termed matrix Dirac-Kohn-Sham restricted magnetic balance resolution of identity for J and K, which takes advantage of the previous restricted magnetic balance formalism and the density fitting approach for the rapid evaluation of density functional theory exchange-correlation response kernels. The new approach is aimed to speedup the bottleneck in the solution of the coupled perturbed equations: evaluation of the matrix elements of the kernel of the exchange-correlation potential. The performance of the new scheme has been tested on a representative set of indirect nuclear spin-spin couplings. The obtained results have been compared with the corresponding results of the reference method with traditional evaluation of the exchange-correlation kernel, i.e., without employing the fitted electron densities. Overall good agreement between both methods was observed, though the new approach tends to give values by about 4%-5% higher than the reference method. On the average, the solution of the coupled perturbed equations with the new scheme is about 8.5 times faster compared to the reference method

Toward nonlinear magnonics: Intensity-dependent spin-wave switching in insulating side-coupled magnetic stripes

Science.gov (United States)

Sadovnikov, A. V.; Odintsov, S. A.; Beginin, E. N.; Sheshukova, S. E.; Sharaevskii, Yu. P.; Nikitov, S. A.

2017-10-01

We demonstrate that the nonlinear spin-wave transport in two laterally parallel magnetic stripes exhibit the intensity-dependent power exchange between the adjacent spin-wave channels. By the means of Brillouin light scattering technique, we investigate collective nonlinear spin-wave dynamics in the presence of magnetodipolar coupling. The nonlinear intensity-dependent effect reveals itself in the spin-wave mode transformation and differential nonlinear spin-wave phase shift in each adjacent magnetic stripe. The proposed analytical theory, based on the coupled Ginzburg-Landau equations, predicts the geometry design involving the reduction of power requirement to the all-magnonic switching. A very good agreement between calculation and experiment was found. In addition, a micromagnetic and finite-element approach has been independently used to study the nonlinear behavior of spin waves in adjacent stripes and the nonlinear transformation of spatial profiles of spin-wave modes. Our results show that the proposed spin-wave coupling mechanism provides the basis for nonlinear magnonic circuits and opens the perspectives for all-magnonic computing architecture.

Coupling a Surface Acoustic Wave to an Electron Spin in Diamond via a Dark State

Directory of Open Access Journals (Sweden)

D. Andrew Golter

2016-12-01

Full Text Available The emerging field of quantum acoustics explores interactions between acoustic waves and artificial atoms and their applications in quantum information processing. In this experimental study, we demonstrate the coupling between a surface acoustic wave (SAW and an electron spin in diamond by taking advantage of the strong strain coupling of the excited states of a nitrogen vacancy center while avoiding the short lifetime of these states. The SAW-spin coupling takes place through a Λ-type three-level system where two ground spin states couple to a common excited state through a phonon-assisted as well as a direct dipole optical transition. Both coherent population trapping and optically driven spin transitions have been realized. The coherent population trapping demonstrates the coupling between a SAW and an electron spin coherence through a dark state. The optically driven spin transitions, which resemble the sideband transitions in a trapped-ion system, can enable the quantum control of both spin and mechanical degrees of freedom and potentially a trapped-ion-like solid-state system for applications in quantum computing. These results establish an experimental platform for spin-based quantum acoustics, bridging the gap between spintronics and quantum acoustics.

Phase dynamics of oscillating magnetizations coupled via spin pumping

Science.gov (United States)

Taniguchi, Tomohiro

2018-05-01

A theoretical formalism is developed to simultaneously solve equation of motion of the magnetizations in two ferromagnets and the spin-pumping induced spin transport equation. Based on the formalism, a coupled motion of the magnetizations in a self-oscillation state is studied. The spin pumping is found to induce an in-phase synchronization of the magnetizations for the oscillation around the easy axis. For an out-of-plane self-oscillation around the hard axis, on the other hand, the spin pumping leads to an in-phase synchronization in a small current region, whereas an antiphase synchronization is excited in a large current region. An analytical theory based on the phase equation reveals that the phase difference between the magnetizations in a steady state depends on the oscillation direction, clockwise or counterclockwise, of the magnetizations.

Reduction of ballistic spin scattering in a spin-FET using stray electric fields

International Nuclear Information System (INIS)

Nemnes, G A; Manolescu, A; Gudmundsson, V

2012-01-01

The quasi-bound states which appear as a consequence of the Rashba spin-orbit (SO) coupling, introduce a strongly irregular behavior of the spin-FET conductance at large Rashba parameter. Moreover, the presence of the bulk inversion asymmetry, i.e. the Dresselhaus SO coupling, may compromise the spin-valve effect even at small values of the Rashba parameter. However, by introducing stray electric fields in addition to the SO couplings, we show that the effect of the SO induced quasi-bound states can be tuned. The oscillations of the spin-resolved conductance become smoother and the control of the spin-FET characteristics becomes possible. For the calculations we employ a multi-channel scattering formalism, based on the R-matrix method extended to spin transport, in the presence of Rashba and Dresselhaus SO couplings.

Spin Funneling for Enhanced Spin Injection into Ferromagnets

Science.gov (United States)

Sayed, Shehrin; Diep, Vinh Q.; Camsari, Kerem Yunus; Datta, Supriyo

2016-07-01

It is well-established that high spin-orbit coupling (SOC) materials convert a charge current density into a spin current density which can be used to switch a magnet efficiently and there is increasing interest in identifying materials with large spin Hall angle for lower switching current. Using experimentally benchmarked models, we show that composite structures can be designed using existing spin Hall materials such that the effective spin Hall angle is larger by an order of magnitude. The basic idea is to funnel spins from a large area of spin Hall material into a small area of ferromagnet using a normal metal with large spin diffusion length and low resistivity like Cu or Al. We show that this approach is increasingly effective as magnets get smaller. We avoid unwanted charge current shunting by the low resistive NM layer utilizing the newly discovered phenomenon of pure spin conduction in ferromagnetic insulators via magnon diffusion. We provide a spin circuit model for magnon diffusion in FMI that is benchmarked against recent experiments and theory.

Structure of large spin expansion of anomalous dimensions at strong coupling

International Nuclear Information System (INIS)

Beccaria, M.; Forini, V.; Tirziu, A.; Tseytlin, A.A.

2009-01-01

The anomalous dimensions of planar N=4 SYM theory operators like tr(ΦD + S Φ) expanded in large spin S have the asymptotics γ=flnS+f c +1/S (f 11 lnS+f 10 )+..., where f (the universal scaling function or cusp anomaly), f c and f mn are given by power series in the 't Hooft coupling λ. The subleading coefficients appear to be related by the so-called functional relation and parity (reciprocity) property of the function expressing γ in terms of the conformal spin of the collinear group. Here we study the structure of such large spin expansion at strong coupling via AdS/CFT, i.e. by using the dual description in terms of folded spinning string in AdS 5 . The large spin expansion of the classical string energy happens to have exactly the same structure as that of γ in the perturbative gauge theory. Moreover, the functional relation and the reciprocity constraints on the coefficients are also satisfied. We compute the leading string 1-loop corrections to the coefficients f c , f 11 , f 10 and verify the functional/reciprocity relations at subleading 1/(√(λ)) order. This provides a strong indication that these relations hold not only in weak coupling (gauge-theory) but also in strong coupling (string-theory) perturbative expansions

Electromagnetic coupling of spins and pseudospins in bilayer graphene

Science.gov (United States)

Winkler, R.; Zülicke, U.

2015-03-01

We present a theoretical study of bilayer-graphene's electronic properties in the presence of electric and magnetic fields. In contrast to known materials, including single-layer graphene, any possible coupling of physical quantities to components of the electric field has a counterpart where the analogous component of the magnetic field couples to exactly the same quantities. For example, a purely electric spin splitting appears as the magneto-electric analogue of the magnetic Zeeman spin splitting. The measurable thermodynamic response induced by magnetic and electric fields is thus completely symmetric. The Pauli magnetization induced by a magnetic field takes exactly the same functional form as the polarization induced by an electric field. Although they seem counterintuitive, our findings are consistent with fundamental principles such as time reversal symmetry. For example, only a magnetic field can give rise to a macroscopic spin polarization, whereas only a perpendicular electric field can induce a macroscopic polarization of the sublattice-related pseudospin in bilayer graphene. These rules enforced by symmetry for the matter-field interactions clarify the nature of spins versus pseudospins. We have obtained numerical values of prefactors for relevant terms. NSF Grant DMR-1310199 and Marsden Fund Contract No. VUW0719.

Spin and charge controlled by antisymmetric spin-orbit coupling in a triangular-triple-quantum-dot Kondo system

Science.gov (United States)

Koga, M.; Matsumoto, M.; Kusunose, H.

2018-05-01

We study a local antisymmetric spin-orbit (ASO) coupling effect on a triangular-triple-quantum-dot (TTQD) system as a theoretical proposal for a new application of the Kondo physics to nanoscale devices. The electric polarization induced by the Kondo effect is strongly correlated with the spin configurations and molecular orbital degrees of freedom in the TTQD. In particular, an abrupt sign reversal of the emergent electric polarization is associated with a quantum critical point in a magnetic field, which can also be controlled by the ASO coupling that changes the mixing weight of different orbital components in the TTQD ground state.

Quantum Stirling heat engine and refrigerator with single and coupled spin systems

Science.gov (United States)

Huang, Xiao-Li; Niu, Xin-Ya; Xiu, Xiao-Ming; Yi, Xue-Xi

2014-02-01

We study the reversible quantum Stirling cycle with a single spin or two coupled spins as the working substance. With the single spin as the working substance, we find that under certain conditions the reversed cycle of a heat engine is NOT a refrigerator, this feature holds true for a Stirling heat engine with an ion trapped in a shallow potential as its working substance. The efficiency of quantum Stirling heat engine can be higher than the efficiency of the Carnot engine, but the performance coefficient of the quantum Stirling refrigerator is always lower than its classical counterpart. With two coupled spins as the working substance, we find that a heat engine can turn to a refrigerator due to the increasing of the coupling constant, this can be explained by the properties of the isothermal line in the magnetic field-entropy plane.

Anisotropic optical absorption induced by Rashba spin-orbit coupling in monolayer phosphorene

Science.gov (United States)

Li, Yuan; Li, Xin; Wan, Qi; Bai, R.; Wen, Z. C.

2018-04-01

We obtain the effective Hamiltonian of the phosphorene including the effect of Rashba spin-orbit coupling in the frame work of the low-energy theory. The spin-splitting energy bands show an anisotropy feature for the wave vectors along kx and ky directions, where kx orients to ΓX direction in the k space. We numerically study the optical absorption of the electrons for different wave vectors with Rashba spin-orbit coupling. We find that the spin-flip transition from the valence band to the conduction band induced by the circular polarized light closes to zero with increasing the x-component wave vector when ky equals to zero, while it can be significantly increased to a large value when ky gets a small value. When the wave vector varies along the ky direction, the spin-flip transition can also increase to a large value, however, which shows an anisotropy feature for the optical absorption. Especially, the spin-conserved transitions keep unchanged and have similar varying trends for different wave vectors. This phenomenon provides a novel route for the manipulation of the spin-dependent property of the fermions in the monolayer phosphorene.

Phase-space curvature in spin-orbit-coupled ultracold atomic systems

Science.gov (United States)

Armaitis, J.; Ruseckas, J.; Anisimovas, E.

2017-04-01

We consider a system with spin-orbit coupling and derive equations of motion which include the effects of Berry curvatures. We apply these equations to investigate the dynamics of particles with equal Rashba-Dresselhaus spin-orbit coupling in one dimension. In our derivation, the adiabatic transformation is performed first and leads to quantum Heisenberg equations of motion for momentum and position operators. These equations explicitly contain position-space, momentum-space, and phase-space Berry curvature terms. Subsequently, we perform the semiclassical approximation and obtain the semiclassical equations of motion. Taking the low-Berry-curvature limit results in equations that can be directly compared to previous results for the motion of wave packets. Finally, we show that in the semiclassical regime, the effective mass of the equal Rashba-Dresselhaus spin-orbit-coupled system can be viewed as a direct effect of the phase-space Berry curvature.

Spin torque on the surface of graphene in the presence of spin orbit splitting

Directory of Open Access Journals (Sweden)

Ji Chen

2013-06-01

Full Text Available We study theoretically the spin transfer torque of a ferromagnetic layer coupled to (deposited onto a graphene surface in the presence of the Rashba spin orbit coupling (RSOC. We show that the RSOC induces an effective magnetic field, which will result in the spin precession of conduction electrons. We derive correspondingly the generalized Landau-Lifshitz-Gilbert (LLG equation, which describes the precessional motion of local magnetization under the influence of the spin orbit effect. Our theoretical estimate indicates that the spin orbit spin torque may have significant effect on the magnetization dynamics of the ferromagnetic layer coupled to the graphene surface.

Coupling of spin and orbital motion of electrons in carbon nanotubes

DEFF Research Database (Denmark)

Kuemmeth, Ferdinand; Ilani, S; Ralph, D C

2008-01-01

Electrons in atoms possess both spin and orbital degrees of freedom. In non-relativistic quantum mechanics, these are independent, resulting in large degeneracies in atomic spectra. However, relativistic effects couple the spin and orbital motion, leading to the well-known fine structure in their...... systems, entailing new design principles for the realization of quantum bits (qubits) in nanotubes and providing a mechanism for all-electrical control of spins in nanotubes....

Structure of large spin expansion of anomalous dimensions at strong coupling

Energy Technology Data Exchange (ETDEWEB)

Beccaria, M. [Physics Department, Salento University and INFN, 73100 Lecce (Italy)], E-mail: matteo.beccaria@le.infn.it; Forini, V. [Humboldt-Universitaet zu Berlin, Institut fuer Physik, D-12489 Berlin (Germany)], E-mail: forini@aei.mpg.de; Tirziu, A. [Department of Physics, Purdue University, W. Lafayette, IN 47907-2036 (United States)], E-mail: atirziu@purdue.edu; Tseytlin, A.A. [Blackett Laboratory, Imperial College, London SW7 2AZ (United Kingdom)], E-mail: tseytlin@imperial.ac.uk

2009-05-01

The anomalous dimensions of planar N=4 SYM theory operators like tr({phi}D{sub +}{sup S}{phi}) expanded in large spin S have the asymptotics {gamma}=flnS+f{sub c}+1/S (f{sub 11}lnS+f{sub 10})+..., where f (the universal scaling function or cusp anomaly), f{sub c} and f{sub mn} are given by power series in the 't Hooft coupling {lambda}. The subleading coefficients appear to be related by the so-called functional relation and parity (reciprocity) property of the function expressing {gamma} in terms of the conformal spin of the collinear group. Here we study the structure of such large spin expansion at strong coupling via AdS/CFT, i.e. by using the dual description in terms of folded spinning string in AdS{sub 5}. The large spin expansion of the classical string energy happens to have exactly the same structure as that of {gamma} in the perturbative gauge theory. Moreover, the functional relation and the reciprocity constraints on the coefficients are also satisfied. We compute the leading string 1-loop corrections to the coefficients f{sub c}, f{sub 11}, f{sub 10} and verify the functional/reciprocity relations at subleading 1/({radical}({lambda})) order. This provides a strong indication that these relations hold not only in weak coupling (gauge-theory) but also in strong coupling (string-theory) perturbative expansions.

The 40th anniversary of the discovery of NMR-chemical shift and nuclear spin-spin coupling

International Nuclear Information System (INIS)

Zhu Zhenghe; Gou Qingquan

1989-01-01

After the discovery of NMR Phenomenon in the physics laboratories of E.M.Purcell at Harvard and F.Bloch at Stanford in 1946, W.G.Proctor and F.C.Yu made the successful discovery of NMR-chemical shift and nuclear spin-spin coupling at Stanford in 1950, Which brought NMR spectroscopy from the physics laboratory to the laboratories of many different fields. This is worth memorizing. Retrospecting the past 40 years, it is sure that chemical shift theory will be much more prosperous prospects

Hybrid spin-nanomechanics with single spins in diamond mechanical oscillators

OpenAIRE

Barfuss, Arne

2017-01-01

Hybrid spin-oscillator systems, formed by single spins coupled to mechanical oscillators, have attracted ever-increasing attention over the past few years, triggered largely by the prospect of employing such devices as high-performance nanoscale sensors or transducers in multi-qubit networks. Provided the spin-oscillator coupling is strong and robust, such systems can even serve as test-beds for studying macroscopic objects in the quantum regime. In this thesis we present a novel hybrid sp...

Electric dipole spin resonance in a quantum spin dimer system driven by magnetoelectric coupling

Science.gov (United States)

Kimura, Shojiro; Matsumoto, Masashige; Akaki, Mitsuru; Hagiwara, Masayuki; Kindo, Koichi; Tanaka, Hidekazu

2018-04-01

In this Rapid Communication, we propose a mechanism for electric dipole active spin resonance caused by spin-dependent electric polarization in a quantum spin gapped system. This proposal was successfully confirmed by high-frequency electron spin resonance (ESR) measurements of the quantum spin dimer system KCuCl3. ESR measurements by an illuminating linearly polarized electromagnetic wave reveal that the optical transition between the singlet and triplet states in KCuCl3 is driven by an ac electric field. The selection rule of the observed transition agrees with the calculation by taking into account spin-dependent electric polarization. We suggest that spin-dependent electric polarization is effective in achieving fast control of quantum spins by an ac electric field.

Inverse spin Hall effect by spin injection

Science.gov (United States)

Liu, S. Y.; Horing, Norman J. M.; Lei, X. L.

2007-09-01

Motivated by a recent experiment [S. O. Valenzuela and M. Tinkham, Nature (London) 442, 176 (2006)], the authors present a quantitative microscopic theory to investigate the inverse spin-Hall effect with spin injection into aluminum considering both intrinsic and extrinsic spin-orbit couplings using the orthogonalized-plane-wave method. Their theoretical results are in good agreement with the experimental data. It is also clear that the magnitude of the anomalous Hall resistivity is mainly due to contributions from extrinsic skew scattering.

Spin-spin interaction between polarized neutrons and polarized 27Al, 59Co, and 93Nb from dispersive optical model and coupled-channel analyses

International Nuclear Information System (INIS)

Nagadi, M.M.; Weisel, G.J.; Walter, R.L.; Delaroche, J.P.; Romain, P.

2004-01-01

Coupled-channel and dispersive-optical model analyses of published neutron scattering and reaction data for 27 Al, 59 Co, and 93 Nb at incident energies between 0.1 and 80 MeV have been performed. The resulting potentials are used to place constraints on the determination of the spin-spin interaction from published spin-spin cross-section measurements. For the three nuclei, the strength of the central real spin-spin potential, which was taken to have a surface plus volume shape, was found to be small. Volume integrals for this central potential component were determined to be in the 4-7 MeV fm 3 range and to decrease somewhat as mass number increases

SOPPA and CCSD vibrational corrections to NMR indirect spin-spin coupling constants of small hydrocarbons

Energy Technology Data Exchange (ETDEWEB)

Faber, Rasmus; Sauer, Stephan P. A. [Department of Chemistry, University of Copenhagen, Universitetsparken 5, DK-2100 Copenhagen Ø (Denmark)

2015-12-31

We present zero-point vibrational corrections to the indirect nuclear spin-spin coupling constants in ethyne, ethene, cyclopropene and allene. The calculations have been carried out both at the level of the second order polarization propagator approximation (SOPPA) employing a new implementation in the DALTON program, at the density functional theory level with the B3LYP functional employing also the Dalton program and at the level of coupled cluster singles and doubles (CCSD) theory employing the implementation in the CFOUR program. Specialized coupling constant basis sets, aug-cc-pVTZ-J, have been employed in the calculations. We find that on average the SOPPA results for both the equilibrium geometry values and the zero-point vibrational corrections are in better agreement with the CCSD results than the corresponding B3LYP results. Furthermore we observed that the vibrational corrections are in the order of 5 Hz for the one-bond carbon-hydrogen couplings and about 1 Hz or smaller for the other couplings apart from the one-bond carbon-carbon coupling (11 Hz) and the two-bond carbon-hydrogen coupling (4 Hz) in ethyne. However, not for all couplings lead the inclusion of zero-point vibrational corrections to better agreement with experiment.

Nonequilibrium Spin Dynamics in a Trapped Fermi Gas with Effective Spin-Orbit Interactions

International Nuclear Information System (INIS)

Stanescu, Tudor D.; Zhang Chuanwei; Galitski, Victor

2007-01-01

We consider a trapped atomic system in the presence of spatially varying laser fields. The laser-atom interaction generates a pseudospin degree of freedom (referred to simply as spin) and leads to an effective spin-orbit coupling for the fermions in the trap. Reflections of the fermions from the trap boundaries provide a physical mechanism for effective momentum relaxation and nontrivial spin dynamics due to the emergent spin-orbit coupling. We explicitly consider evolution of an initially spin-polarized Fermi gas in a two-dimensional harmonic trap and derive nonequilibrium behavior of the spin polarization. It shows periodic echoes with a frequency equal to the harmonic trapping frequency. Perturbations, such as an asymmetry of the trap, lead to the suppression of the spin echo amplitudes. We discuss a possible experimental setup to observe spin dynamics and provide numerical estimates of relevant parameters

Role of spin-orbit coupling in the Kugel-Khomskii model on the honeycomb lattice

Science.gov (United States)

Koga, Akihisa; Nakauchi, Shiryu; Nasu, Joji

2018-03-01

We study the effective spin-orbital model for honeycomb-layered transition metal compounds, applying the second-order perturbation theory to the three-orbital Hubbard model with the anisotropic hoppings. This model is reduced to the Kitaev model in the strong spin-orbit coupling limit. Combining the cluster mean-field approximations with the exact diagonalization, we treat the Kugel-Khomskii type superexchange interaction and spin-orbit coupling on an equal footing to discuss ground-state properties. We find that a zigzag ordered state is realized in the model within nearest-neighbor interactions. We clarify how the ordered state competes with the nonmagnetic state, which is adiabatically connected to the quantum spin liquid state realized in a strong spin-orbit coupling limit. Thermodynamic properties are also addressed. The present paper should provide another route to account for the Kitaev-based magnetic properties in candidate materials.

On the Convergence of the ccJ-pVXZ and pcJ-n Basis Sets in CCSD Calculations of Nuclear Spin-Spin Coupling Constants

DEFF Research Database (Denmark)

Faber, Rasmus; Sauer, Stephan P. A.

2018-01-01

The basis set convergence of nuclear spin-spin coupling constants (SSCC) calculated at the coupled cluster singles and doubles (CCSD) level has been investigated for ten difficult molecules. Eight of the molecules contain fluorine atoms and nine contain double or triple bonds. Results obtained...

ac spin-Hall effect

International Nuclear Information System (INIS)

Entin-Wohlman, O.

2005-01-01

Full Text:The spin-Hall effect is described. The Rashba and Dresselhaus spin-orbit interactions are both shown to yield the low temperature spin-Hall effect for strongly localized electrons coupled to phonons. A frequency-dependent electric field E(ω) generates a spin-polarization current, normal to E, due to interference of hopping paths. At zero temperature the corresponding spin-Hall conductivity is real and is proportional to ω 2 . At non-zero temperatures the coupling to the phonons yields an imaginary term proportional to ω. The interference also yields persistent spin currents at thermal equilibrium, at E = 0. The contributions from the Dresselhaus and Rashba interactions to the interference oppose each other

A low-temperature derivation of spin-spin exchange in Kondo lattice model

International Nuclear Information System (INIS)

Feng Szeshiang; Mochena, Mogus

2005-01-01

Using Hubbard-Stratonovich transformation and drone-fermion representations for spin-12 and for spin-32, which is presented for the first time, we make a path-integral formulation of the Kondo lattice model. In the case of weak coupling and low temperature, the functional integral over conduction fermions can be approximated to the quadratic order and this gives the well-known RKKY interaction. In the case of strong coupling, the same quadratic approximation leads to an effective local spin-spin interaction linear in hopping energy t

A low-temperature derivation of spin-spin exchange in Kondo lattice model

Energy Technology Data Exchange (ETDEWEB)

Feng Szeshiang [Physics Department, Florida A and M University, Tallahassee, FL 32307 (United States)]. E-mail: shixiang.feng@famu.edu; Mochena, Mogus [Physics Department, Florida A and M University, Tallahassee, FL 32307 (United States)

2005-11-01

Using Hubbard-Stratonovich transformation and drone-fermion representations for spin-12 and for spin-32, which is presented for the first time, we make a path-integral formulation of the Kondo lattice model. In the case of weak coupling and low temperature, the functional integral over conduction fermions can be approximated to the quadratic order and this gives the well-known RKKY interaction. In the case of strong coupling, the same quadratic approximation leads to an effective local spin-spin interaction linear in hopping energy t.

Spin-Orbit Coupled Quantum Magnetism in the 3D-Honeycomb Iridates

Science.gov (United States)

Kimchi, Itamar

In this doctoral dissertation, we consider the significance of spin-orbit coupling for the phases of matter which arise for strongly correlated electrons. We explore emergent behavior in quantum many-body systems, including symmetry-breaking orders, quantum spin liquids, and unconventional superconductivity. Our study is cemented by a particular class of Mott-insulating materials, centered around a family of two- and three-dimensional iridium oxides, whose honeycomb-like lattice structure admits peculiar magnetic interactions, the so-called Kitaev exchange. By analyzing recent experiments on these compounds, we show that this unconventional exchange is the key ingredient in describing their magnetism, and then use a combination of numerical and analytical techniques to investigate the implications for the phase diagram as well as the physics of the proximate three-dimensional quantum spin liquid phases. These long-ranged-entangled fractionalized phases should exhibit special features, including finite-temperature stability as well as unconventional high-Tc superconductivity upon charge-doping, which should aid future experimental searches for spin liquid physics. Our study explores the nature of frustration and fractionalization which can arise in quantum systems in the presence of strong spin-orbit coupling.

Spin transport in spin filtering magnetic tunneling junctions.

Science.gov (United States)

Li, Yun; Lee, Eok Kyun

2007-11-01

Taking into account spin-orbit coupling and s-d interaction, we investigate spin transport properties of the magnetic tunneling junctions with spin filtering barrier using Landauer-Büttiker formalism implemented with the recursive algorithm to calculate the real-space Green function. We predict completely different bias dependence of negative tunnel magnetoresistance (TMR) between the systems composed of nonmagnetic electrode (NM)/ferromagnetic barrier (FB)/ferromagnet (FM) and NM/FB/FM/NM spin filtering tunnel junctions (SFTJs). Analyses of the results provide us possible ways of designing the systems which modulate the TMR in the negative magnetoresistance regime.

Second post-Newtonian Lagrangian dynamics of spinning compact binaries

Energy Technology Data Exchange (ETDEWEB)

Huang, Li; Wu, Xin [Nanchang University, Department of Physics and Institute of Astronomy, Nanchang (China); Ma, DaZhu [Hubei University for Nationalities, School of Science, Enshi (China)

2016-09-15

The leading-order spin-orbit coupling is included in a post-Newtonian Lagrangian formulation of spinning compact binaries, which consists of the Newtonian term, first post-Newtonian (1PN) and 2PN non-spin terms and 2PN spin-spin coupling. This leads to a 3PN spin-spin coupling occurring in the derived Hamiltonian. The spin-spin couplings are mainly responsible for chaos in the Hamiltonians. However, the 3PN spin-spin Hamiltonian is small and has different signs, compared with the 2PN spin-spin Hamiltonian equivalent to the 2PN spin-spin Lagrangian. As a result, the probability of the occurrence of chaos in the Lagrangian formulation without the spin-orbit coupling is larger than that in the Lagrangian formulation with the spin-orbit coupling. Numerical evidences support this claim. (orig.)

Coherent manipulation of dipolar coupled spins in an anisotropic environment

Science.gov (United States)

Baibekov, E. I.; Gafurov, M. R.; Zverev, D. G.; Kurkin, I. N.; Malkin, B. Z.; Barbara, B.

2014-11-01

We study coherent dynamics in a system of dipolar coupled spin qubits diluted in a solid and subjected to a driving microwave field. In the case of rare earth ions, an anisotropic crystal background results in anisotropic g tensor and thus modifies the dipolar coupling. We develop a microscopic theory of spin relaxation in a transient regime for the frequently encountered case of axially symmetric crystal field. The calculated decoherence rate is nonlinear in the Rabi frequency. We show that the direction of a static magnetic field that corresponds to the highest spin g factor is preferable in order to obtain a higher number of coherent qubit operations. The results of calculations are in excellent agreement with our experimental data on Rabi oscillations recorded for a series of CaW O4 crystals with different concentrations of N d3 + ions.

Microscopic studies of nonlocal spin dynamics and spin transport (invited)

Energy Technology Data Exchange (ETDEWEB)

Adur, Rohan; Du, Chunhui; Cardellino, Jeremy; Scozzaro, Nicolas; Wolfe, Christopher S.; Wang, Hailong; Herman, Michael; Bhallamudi, Vidya P.; Pelekhov, Denis V.; Yang, Fengyuan; Hammel, P. Chris, E-mail: hammel@physics.osu.edu [Department of Physics, The Ohio State University, Columbus, Ohio 43210 (United States)

2015-05-07

Understanding the behavior of spins coupling across interfaces in the study of spin current generation and transport is a fundamental challenge that is important for spintronics applications. The transfer of spin angular momentum from a ferromagnet into an adjacent normal material as a consequence of the precession of the magnetization of the ferromagnet is a process known as spin pumping. We find that, in certain circumstances, the insertion of an intervening normal metal can enhance spin pumping between an excited ferromagnetic magnetization and a normal metal layer as a consequence of improved spin conductance matching. We have studied this using inverse spin Hall effect and enhanced damping measurements. Scanned probe magnetic resonance techniques are a complementary tool in this context offering high resolution magnetic resonance imaging, localized spin excitation, and direct measurement of spin lifetimes or damping. Localized magnetic resonance studies of size-dependent spin dynamics in the absence of lithographic confinement in both ferromagnets and paramagnets reveal the close relationship between spin transport and spin lifetime at microscopic length scales. Finally, detection of ferromagnetic resonance of a ferromagnetic film using the photoluminescence of nitrogen vacancy spins in neighboring nanodiamonds demonstrates long-range spin transport between insulating materials, indicating the complexity and generality of spin transport in diverse, spatially separated, material systems.

Microscopic studies of nonlocal spin dynamics and spin transport (invited)

Science.gov (United States)

Adur, Rohan; Du, Chunhui; Cardellino, Jeremy; Scozzaro, Nicolas; Wolfe, Christopher S.; Wang, Hailong; Herman, Michael; Bhallamudi, Vidya P.; Pelekhov, Denis V.; Yang, Fengyuan; Hammel, P. Chris

2015-05-01

Understanding the behavior of spins coupling across interfaces in the study of spin current generation and transport is a fundamental challenge that is important for spintronics applications. The transfer of spin angular momentum from a ferromagnet into an adjacent normal material as a consequence of the precession of the magnetization of the ferromagnet is a process known as spin pumping. We find that, in certain circumstances, the insertion of an intervening normal metal can enhance spin pumping between an excited ferromagnetic magnetization and a normal metal layer as a consequence of improved spin conductance matching. We have studied this using inverse spin Hall effect and enhanced damping measurements. Scanned probe magnetic resonance techniques are a complementary tool in this context offering high resolution magnetic resonance imaging, localized spin excitation, and direct measurement of spin lifetimes or damping. Localized magnetic resonance studies of size-dependent spin dynamics in the absence of lithographic confinement in both ferromagnets and paramagnets reveal the close relationship between spin transport and spin lifetime at microscopic length scales. Finally, detection of ferromagnetic resonance of a ferromagnetic film using the photoluminescence of nitrogen vacancy spins in neighboring nanodiamonds demonstrates long-range spin transport between insulating materials, indicating the complexity and generality of spin transport in diverse, spatially separated, material systems.

Microscopic studies of nonlocal spin dynamics and spin transport (invited)

International Nuclear Information System (INIS)

Adur, Rohan; Du, Chunhui; Cardellino, Jeremy; Scozzaro, Nicolas; Wolfe, Christopher S.; Wang, Hailong; Herman, Michael; Bhallamudi, Vidya P.; Pelekhov, Denis V.; Yang, Fengyuan; Hammel, P. Chris

2015-01-01

Understanding the behavior of spins coupling across interfaces in the study of spin current generation and transport is a fundamental challenge that is important for spintronics applications. The transfer of spin angular momentum from a ferromagnet into an adjacent normal material as a consequence of the precession of the magnetization of the ferromagnet is a process known as spin pumping. We find that, in certain circumstances, the insertion of an intervening normal metal can enhance spin pumping between an excited ferromagnetic magnetization and a normal metal layer as a consequence of improved spin conductance matching. We have studied this using inverse spin Hall effect and enhanced damping measurements. Scanned probe magnetic resonance techniques are a complementary tool in this context offering high resolution magnetic resonance imaging, localized spin excitation, and direct measurement of spin lifetimes or damping. Localized magnetic resonance studies of size-dependent spin dynamics in the absence of lithographic confinement in both ferromagnets and paramagnets reveal the close relationship between spin transport and spin lifetime at microscopic length scales. Finally, detection of ferromagnetic resonance of a ferromagnetic film using the photoluminescence of nitrogen vacancy spins in neighboring nanodiamonds demonstrates long-range spin transport between insulating materials, indicating the complexity and generality of spin transport in diverse, spatially separated, material systems

Tunneling conductance of a two-dimensional electron gas with Dresselhaus spin-orbit coupling

International Nuclear Information System (INIS)

Srisongmuang, B.; Ka-oey, A.

2012-01-01

We theoretically studied the spin-dependent charge transport in a two-dimensional electron gas with Dresselhaus spin-orbit coupling (DSOC) and metal junctions. It is shown that the DSOC energy can be directly measured from the tunneling conductance spectrum. We found that spin polarization of the conductance in the propagation direction can be obtained by injecting from the DSOC system. We also considered the effect of the interfacial scattering barrier (both spin-flip and non-spin-flip scattering) on the overall conductance and the spin polarization of the conductance. It is found that the increase of spin-flip scattering can enhance the conductance under certain conditions. Moreover, both types of scattering can increase the spin polarization below the branches crossing of the energy band. - Highlights: → DSOC energy can be directly measured from tunneling conductance spectrum. → Spin polarization of conductance in the propagation direction can be obtained by injecting from DSOC system. → Both types of scattering can increase spin polarization.

Parity Anomaly and Spin Transmutation in Quantum Spin Hall Josephson Junctions.

Science.gov (United States)

Peng, Yang; Vinkler-Aviv, Yuval; Brouwer, Piet W; Glazman, Leonid I; von Oppen, Felix

2016-12-23

We study the Josephson effect in a quantum spin Hall system coupled to a localized magnetic impurity. As a consequence of the fermion parity anomaly, the spin of the combined system of impurity and spin-Hall edge alternates between half-integer and integer values when the superconducting phase difference across the junction advances by 2π. This leads to characteristic differences in the splittings of the spin multiplets by exchange coupling and single-ion anisotropy at phase differences, for which time-reversal symmetry is preserved. We discuss the resulting 8π-periodic (or Z_{4}) fractional Josephson effect in the context of recent experiments.

Electrically tunable spin polarization in silicene: A multi-terminal spin density matrix approach

International Nuclear Information System (INIS)

Chen, Son-Hsien

2016-01-01

Recent realized silicene field-effect transistor yields promising electronic applications. Using a multi-terminal spin density matrix approach, this paper presents an analysis of the spin polarizations in a silicene structure of the spin field-effect transistor by considering the intertwined intrinsic and Rashba spin–orbit couplings, gate voltage, Zeeman splitting, as well as disorder. Coexistence of the stagger potential and intrinsic spin–orbit coupling results in spin precession, making any in-plane polarization directions reachable by the gate voltage; specifically, the intrinsic coupling allows one to electrically adjust the in-plane components of the polarizations, while the Rashba coupling to adjust the out-of-plan polarizations. Larger electrically tunable ranges of in-plan polarizations are found in oppositely gated silicene than in the uniformly gated silicene. Polarizations in different phases behave distinguishably in weak disorder regime, while independent of the phases, stronger disorder leads to a saturation value. - Highlights: • Density matrix with spin rotations enables multi-terminal arbitrary spin injections. • Gate-voltage tunable in-plane polarizations require intrinsic SO coupling. • Gate-voltage tunable out-of-plane polarizations require Rashba SO coupling. • Oppositely gated silicene yields a large tunable range of in-plan polarizations. • Polarizations in different phases behave distinguishably only in weak disorder.

Phase transitions and thermal entanglement of the distorted Ising-Heisenberg spin chain: topology of multiple-spin exchange interactions in spin ladders

Science.gov (United States)

Arian Zad, Hamid; Ananikian, Nerses

2017-11-01

We consider a symmetric spin-1/2 Ising-XXZ double sawtooth spin ladder obtained from distorting a spin chain, with the XXZ interaction between the interstitial Heisenberg dimers (which are connected to the spins based on the legs via an Ising-type interaction), the Ising coupling between nearest-neighbor spins of the legs and rungs spins, respectively, and additional cyclic four-spin exchange (ring exchange) in the square plaquette of each block. The presented analysis supplemented by results of the exact solution of the model with infinite periodic boundary implies a rich ground state phase diagram. As well as the quantum phase transitions, the characteristics of some of the thermodynamic parameters such as heat capacity, magnetization and magnetic susceptibility are investigated. We prove here that among the considered thermodynamic and thermal parameters, solely heat capacity is sensitive versus the changes of the cyclic four-spin exchange interaction. By using the heat capacity function, we obtain a singularity relation between the cyclic four-spin exchange interaction and the exchange coupling between pair spins on each rung of the spin ladder. All thermal and thermodynamic quantities under consideration should be investigated by regarding those points which satisfy the singularity relation. The thermal entanglement within the Heisenberg spin dimers is investigated by using the concurrence, which is calculated from a relevant reduced density operator in the thermodynamic limit.

Inverse spin Hall effect induced by spin pumping into semiconducting ZnO

Energy Technology Data Exchange (ETDEWEB)

Lee, Jung-Chuan [Institute of Physics, Academia Sinica, Taipei 11529, Taiwan (China); Huang, Leng-Wei [Graduate Institute of Applied Physics, National Chengchi University, Taipei 11605, Taiwan (China); Hung, Dung-Shing, E-mail: dshung@mail.mcu.edu.tw [Institute of Physics, Academia Sinica, Taipei 11529, Taiwan (China); Department of Information and Telecommunications Engineering, Ming Chuan University, Taipei 111, Taiwan (China); Chiang, Tung-Han [Department of Physics, National Cheng Kung University, Tainan 70101, Taiwan (China); Huang, J. C. A., E-mail: jcahuang@mail.ncku.edu.tw [Department of Physics, National Cheng Kung University, Tainan 70101, Taiwan (China); Advanced Optoelectronic Technology Center, National Cheng Kung University, Tainan 70101, Taiwan (China); Liang, Jun-Zhi [Advanced Optoelectronic Technology Center, National Cheng Kung University, Tainan 70101, Taiwan (China); Department of Physics, Fu Jen Catholic University, Taipei 242, Taiwan (China); Lee, Shang-Fan, E-mail: leesf@phys.sinica.edu.tw [Institute of Physics, Academia Sinica, Taipei 11529, Taiwan (China); Graduate Institute of Applied Physics, National Chengchi University, Taipei 11605, Taiwan (China)

2014-02-03

The inverse spin Hall effect (ISHE) of n-type semiconductor ZnO thin films with weak spin-orbit coupling has been observed by utilizing the spin pumping method. In the ferromagnetic resonance condition, the spin pumping driven by the dynamical exchange interaction of a permalloy film injects a pure spin current into the adjacent ZnO layer. This spin current gives rise to a DC voltage through the ISHE in the ZnO layer, and the DC voltage is proportional to the microwave excitation power. The effect is sizeable even when the spin backflow is considered.

Inverse spin Hall effect induced by spin pumping into semiconducting ZnO

International Nuclear Information System (INIS)

Lee, Jung-Chuan; Huang, Leng-Wei; Hung, Dung-Shing; Chiang, Tung-Han; Huang, J. C. A.; Liang, Jun-Zhi; Lee, Shang-Fan

2014-01-01

The inverse spin Hall effect (ISHE) of n-type semiconductor ZnO thin films with weak spin-orbit coupling has been observed by utilizing the spin pumping method. In the ferromagnetic resonance condition, the spin pumping driven by the dynamical exchange interaction of a permalloy film injects a pure spin current into the adjacent ZnO layer. This spin current gives rise to a DC voltage through the ISHE in the ZnO layer, and the DC voltage is proportional to the microwave excitation power. The effect is sizeable even when the spin backflow is considered

Coupled dynamics of interacting spin-1 bosons in a double-well potential

Science.gov (United States)

Carvalho, D. W. S.; Foerster, A.; Gusmão, M. A.

2018-03-01

We present a detailed analysis of dynamical processes involving two or three particles in a double-well potential. Motivated by experimental realizations of such a system with optically trapped cold atoms, we focus on spin-1 bosons with special attention on the effects of a spin-dependent interaction in addition to the usual Hubbard-like repulsive one. For a sufficiently weak tunneling amplitude in comparison to the dominant Hubbard coupling, particle motion is strongly correlated, occurring only under fine-tuned relationships between well-depth asymmetry and interactions. We highlight processes involving tunneling of coupled particle pairs and triads, emphasizing the role of the spin-dependent interaction in resonance conditions.

Discovery of highly spin-polarized conducting surface states in the strong spin-orbit coupling semiconductor Sb2Se3

Science.gov (United States)

Das, Shekhar; Sirohi, Anshu; Kumar Gupta, Gaurav; Kamboj, Suman; Vasdev, Aastha; Gayen, Sirshendu; Guptasarma, Prasenjit; Das, Tanmoy; Sheet, Goutam

2018-06-01

Majority of the A2B3 -type chalcogenide systems with strong spin-orbit coupling (SOC), such as Bi2Se3,Bi2Te3 , and Sb2Te3 , etc., are topological insulators. One important exception is Sb2Se3 where a topological nontrivial phase was argued to be possible under ambient conditions, but such a phase could be detected to exist only under pressure. In this paper, we show that Sb2Se3 like Bi2Se3 displays a generation of highly spin-polarized current under mesoscopic superconducting point contacts as measured by point-contact Andreev reflection spectroscopy. In addition, we observe a large negative and anisotropic magnetoresistance of the mesoscopic metallic point contacts formed on Sb2Se3 . Our band-structure calculations confirm the trivial nature of Sb2Se3 crystals and reveal two trivial surface states one of which shows large spin splitting due to Rashba-type SOC. The observed high spin polarization and related phenomena in Sb2Se3 can be attributed to this spin splitting.

Energy spectrum, the spin polarization, and the optical selection rules of the Kronig-Penney superlattice model with spin-orbit coupling

Science.gov (United States)

Li, Rui

2018-02-01

The Kronig-Penney model, an exactly solvable one-dimensional model of crystal in solid physics, shows how the allowed and forbidden bands are formed in solids. In this paper, we study this model in the presence of both strong spin-orbit coupling and the Zeeman field. We analytically obtain four transcendental equations that represent an implicit relation between the energy and the Bloch wave vector. Solving these four transcendental equations, we obtain the spin-orbital bands exactly. In addition to the usual band gap opened at the boundary of the Brillouin zone, a much larger spin-orbital band gap is also opened at some special sites inside the Brillouin zone. The x component of the spin-polarization vector is an even function of the Bloch wave vector, while the z component of the spin-polarization vector is an odd function of the Bloch wave vector. At the band edges, the optical transition rates between adjacent bands are nonzero.

The /sup 13/C-/sup 13/C spin-spin coupling constants and the conformational equilibrium of alkyl phenyl sulfides

Energy Technology Data Exchange (ETDEWEB)

Krividin, L.B.; Kalabin, G.A.

1985-08-10

The authors measure the direct geminal and vicinal spinspin coupling constants between the C-13 nuclei of the phenyl group in the series of alkyl phenyl sulfides C/sub 6/H/sub 5/SR. It was shown that the variation in most of the discussed constants is determined by the ratio of the planar and orthogonal conformers. Linear relationships were obtained between the C-13-C-13 constants and the fractions of the planar conformer. The C-13-C-13 spin-spin coupling constants in the planar and orthogonal conformers of the compounds were calculated by means of empirical relationships.

Antiferromagnetic Spin Coupling between Rare Earth Adatoms and Iron Islands Probed by Spin-Polarized Tunneling.

Science.gov (United States)

Coffey, David; Diez-Ferrer, José Luis; Serrate, David; Ciria, Miguel; de la Fuente, César; Arnaudas, José Ignacio

2015-09-03

High-density magnetic storage or quantum computing could be achieved using small magnets with large magnetic anisotropy, a requirement that rare-earth iron alloys fulfill in bulk. This compelling property demands a thorough investigation of the magnetism in low dimensional rare-earth iron structures. Here, we report on the magnetic coupling between 4f single atoms and a 3d magnetic nanoisland. Thulium and lutetium adatoms deposited on iron monolayer islands pseudomorphically grown on W(110) have been investigated at low temperature with scanning tunneling microscopy and spectroscopy. The spin-polarized current indicates that both kind of adatoms have in-plane magnetic moments, which couple antiferromagnetically with their underlying iron islands. Our first-principles calculations explain the observed behavior, predicting an antiparallel coupling of the induced 5d electrons magnetic moment of the lanthanides with the 3d magnetic moment of iron, as well as their in-plane orientation, and pointing to a non-contribution of 4f electrons to the spin-polarized tunneling processes in rare earths.

Classical description of dynamical many-body systems with central forces, spin-orbit forces and spin-spin forces

International Nuclear Information System (INIS)

Goepfert, A.

1994-01-01

This thesis develops a new model, and related numerical methods, to describe classical time-dependent many-body systems interacting through central forces, spin-orbit forces and spin-spin forces. The model is based on two-particle interactions. The two-body forces consist of attractive and repulsive parts. In this model the investigated multi-particle systems are self-bound. Also the total potential of the whole ensemble is derived from the two-particle potential and is not imposed 'from outside'. Each particle has the three degrees of freedom of its centre-of-mass motion and the spin degree of freedom. The model allows for the particles to be either charged or uncharged. Furthermore, each particle has an angular momentum, an intrinsic spin, and a magnetic dipole moment. Through the electromagnetic forces between these charges and moments there arise dynamical couplings between them. The internal interactions between the charges and moments are well described by electromagnetic coupling mechanisms. In fact, compared to conventional classical molecular dynamics calculations in van der Waals clusters, which have no spin degrees of freedom, or for Heisenberg spin Systems, which have no orbital degrees of freedom, the model presented here contains both types of degrees of freedom with a highly non-trivial coupling. The model allows to study the fundamental effects resulting from the dynamical coupling of the spin and the orbital-motion sub-systems. In particular, the dynamics of the particle mass points show a behaviour basically different from the one of particles in a potential with only central forces. Furthermore, a special type of quenching procedure was invented, which tends to drive the multi-particle Systems into states with highly periodic, non-ergodic behaviour. Application of the model to cluster simulations has provided evidence that the model can also be used to investigate items like solid-to-liquid phase transitions (melting), isomerism and specific heat

Spin relaxation in quantum dots: Role of the phonon modulated spin-orbit interaction

Science.gov (United States)

Alcalde, A. M.; Romano, C. L.; Sanz, L.; Marques, G. E.

2010-01-01

We calculate the spin relaxation rates in a parabolic InSb quantum dots due to the spin interaction with acoustical phonons. We considered the deformation potential mechanism as the dominant electron-phonon coupling in the Pavlov-Firsov spin-phonon Hamiltonian. We analyze the behavior of the spin relaxation rates as a function of an external magnetic field and mean quantum dot radius. Effects of the spin admixture due to Dresselhaus contribution to spin-orbit interaction are also discussed.

Spin Currents and Spin Orbit Torques in Ferromagnets and Antiferromagnets

Science.gov (United States)

Hung, Yu-Ming

This thesis focuses on the interactions of spin currents and materials with magnetic order, e.g., ferromagnetic and antiferromagnetic thin films. The spin current is generated in two ways. First by spin-polarized conduction-electrons associated with the spin Hall effect in heavy metals (HMs) and, second, by exciting spin-waves in ferrimagnetic insulators using a microwave frequency magnetic field. A conduction-electron spin current can be generated by spin-orbit coupling in a heavy non-magnetic metal and transfer its spin angular momentum to a ferromagnet, providing a means of reversing the magnetization of perpendicularly magnetized ultrathin films with currents that flow in the plane of the layers. The torques on the magnetization are known as spin-orbit torques (SOT). In the first part of my thesis project I investigated and contrasted the quasistatic (slowly swept current) and pulsed current-induced switching characteristics of micrometer scale Hall crosses consisting of very thin (magnetized CoFeB layers on beta-Ta. While complete magnetization reversal occurs at a threshold current density in the quasistatic case, pulses with short duration (≤10 ns) and larger amplitude (≃10 times the quasistatic threshold current) lead to only partial magnetization reversal and domain formation. The partial reversal is associated with the limited time for reversed domain expansion during the pulse. The second part of my thesis project studies and considers applications of SOT-driven domain wall (DW) motion in a perpendicularly magnetized ultrathin ferromagnet sandwiched between a heavy metal and an oxide. My experiment results demonstrate that the DW motion can be explained by a combination of the spin Hall effect, which generates a SOT, and Dzyaloshinskii-Moriya interaction, which stabilizes chiral Neel-type DW. Based on SOT-driven DW motion and magnetic coupling between electrically isolated ferromagnetic elements, I proposed a new type of spin logic devices. I then

The role of Rashba spin-orbit coupling in valley-dependent transport of Dirac fermions

Energy Technology Data Exchange (ETDEWEB)

Hasanirok, Kobra; Mohammadpour, Hakimeh

2017-01-01

At this work, spin- and valley-dependent electron transport through graphene and silicene layers are studied in the presence of Rashba spin- orbit coupling. We find that the transport properties of the related ferromagnetic/normal/ferromagnetic structure depend on the relevant parameters. A fully valley- and spin- polarized current is obtained. As another result, Rashba spin-orbit interaction plays important role in controlling the transmission characteristics.

Maximal Rashba-like spin splitting via kinetic-energy-coupled inversion-symmetry breaking

Science.gov (United States)

Sunko, Veronika; Rosner, H.; Kushwaha, P.; Khim, S.; Mazzola, F.; Bawden, L.; Clark, O. J.; Riley, J. M.; Kasinathan, D.; Haverkort, M. W.; Kim, T. K.; Hoesch, M.; Fujii, J.; Vobornik, I.; MacKenzie, A. P.; King, P. D. C.

2017-09-01

Engineering and enhancing the breaking of inversion symmetry in solids—that is, allowing electrons to differentiate between ‘up’ and ‘down’—is a key goal in condensed-matter physics and materials science because it can be used to stabilize states that are of fundamental interest and also have potential practical applications. Examples include improved ferroelectrics for memory devices and materials that host Majorana zero modes for quantum computing. Although inversion symmetry is naturally broken in several crystalline environments, such as at surfaces and interfaces, maximizing the influence of this effect on the electronic states of interest remains a challenge. Here we present a mechanism for realizing a much larger coupling of inversion-symmetry breaking to itinerant surface electrons than is typically achieved. The key element is a pronounced asymmetry of surface hopping energies—that is, a kinetic-energy-coupled inversion-symmetry breaking, the energy scale of which is a substantial fraction of the bandwidth. Using spin- and angle-resolved photoemission spectroscopy, we demonstrate that such a strong inversion-symmetry breaking, when combined with spin-orbit interactions, can mediate Rashba-like spin splittings that are much larger than would typically be expected. The energy scale of the inversion-symmetry breaking that we achieve is so large that the spin splitting in the CoO2- and RhO2-derived surface states of delafossite oxides becomes controlled by the full atomic spin-orbit coupling of the 3d and 4d transition metals, resulting in some of the largest known Rashba-like spin splittings. The core structural building blocks that facilitate the bandwidth-scaled inversion-symmetry breaking are common to numerous materials. Our findings therefore provide opportunities for creating spin-textured states and suggest routes to interfacial control of inversion-symmetry breaking in designer heterostructures of oxides and other material classes.

Odd number of coupled antiferromagnetic anisotropic Heisenberg chains: Spin wave theory

International Nuclear Information System (INIS)

Benyoussef, A.

1996-10-01

The effect of the chain and perpendicular anisotropies on the energy gap for odd number of coupled quantum spin-1/2 antiferromagnetic anisotropic Heisenberg chains is investigated using a spin wave theory. The energy gap opens above a critical anisotropic value. The known results of the isotropic case have been obtained. (author). 11 refs, 4 figs

Some exact identities connecting one- and two-particle Green's functions in spin-orbit coupling systems

International Nuclear Information System (INIS)

Yang Huatong

2007-01-01

Some exact identities connecting one- and two-particle Green's functions in the presence of spin-orbit coupling have been derived. These identities are similar to the Ward identity in usual quantum transport theory of electrons. A satisfying approximate calculation of the spin transport in spin-orbit coupling system should also preserve these identities, just as the Ward identities should be remained in the usual electronic transport theory

Scattering resonances in a low-dimensional Rashba-Dresselhaus spin-orbit coupled quantum gas

Science.gov (United States)

Wang, Su-Ju; Blume, D.

2017-04-01

Confinement-induced resonances allow for the tuning of the effective one-dimensional coupling constant. When the scattering state associated with the ground transverse mode is brought into resonance with the bound state attached to the energetically excited transverse modes, the atoms interact through an infinitely strong repulsion. This provides a route to realize the Tonks-Girardeau gas. On the other hand, the realization of synthetic gauge fields in cold atomic systems has attracted a lot of attention. For instance, bound-state formation is found to be significantly modified in the presence of spin-orbit coupling in three dimensions. This motivates us to study ultracold collisions between two Rashba-Dresselhaus spin-orbit coupled atoms in a quasi-one-dimensional geometry. We develop a multi-channel scattering formalism that accounts for the external transverse confinement and the spin-orbit coupling terms. The interplay between these two single-particle terms is shown to give rise to new scattering resonances. In particular, it is analyzed what happens when the scattering energy crosses the various scattering thresholds that arise from the single-particle confinement and the spin-orbit coupling. Support by the NSF is gratefully acknowledged.

Photon and spin dependence of the resonance line shape in the strong coupling regime

NARCIS (Netherlands)

Miyashita, Seiji; Shirai, Tatsuhiko; Mori, Takashi; De Raedt, Hans; Bertaina, Sylvain; Chiorescu, Irinel

2012-01-01

We study the quantum dynamics of a spin ensemble coupled to cavity photons. Recently, related experimental results have been reported, showing the existence of the strong coupling regime in such systems. We study the eigenenergy distribution of the multi-spin system (following the Tavis-Cummings

Spin Chern number and topological phase transition on the Lieb lattice with spin–orbit coupling

International Nuclear Information System (INIS)

Chen, Rui; Zhou, Bin

2017-01-01

We propose that quantum anomalous Hall effect may occur in the Lieb lattice, when Rashba spin–orbit coupling, spin-independent and spin-dependent staggered potentials are introduced into the lattice. It is found that spin Chern numbers of two degenerate flat bands change from 0 to ±2 due to Rashba spin–orbit coupling effect. The inclusion of Rashba spin–orbit coupling and two kinds of staggered potentials opens a gap between the two flat bands. The topological property of the gap is determined by the amplitudes of Rashba spin–orbit coupling and staggered potentials, and thus the topological phase transition from quantum anomalous Hall effect to normal insulator can occur. Finally, the topological phase transition from quantum spin Hall state to normal insulator is discussed when Rashba spin–orbit coupling and intrinsic spin–orbit coupling coexist in the Lieb lattice. - Highlights: • Spin Chern numbers of the bulk states on the Lieb lattice are calculated. • RSOC plays an important role on the topological phase transition on the Lieb lattice. • Quantum anomalous Hall effect can occur due to RSOC and staggered potentials. • Topological phase transition can occur when ISOC and RSOC coexist.

Nuclear spin-spin coupling constants of linear carbon chains terminated by coronene molecules: a first principles study

International Nuclear Information System (INIS)

Oliveira, Joao Paulo Cavalcante; Mota, F. de Brito; Rivelino, Roberto

2011-01-01

Full text. Carbon nano wires made of long linear atomic chains have attracted considerable interest due to their potential applications in nano electronics. We report a density-functional-theory study of the nuclear spin-spin coupling constants for nano assemblies made of two coronene molecules bridged by carbon linear chains, considering distinct sizes and spin multiplicities. Also, we examine the effects of two terminal conformations (syn and anti) of the terminal anchor pieces on the magnetic properties of the carbon chains via 13 C NMR calculations. Our results reveal that simplified chemical models such as those based on cumulenes or polyynes are not appropriate to describe the linear chains with sp 2 terminations. For these types of atomic chains, the electronic ground state of the even-numbered chains can be singlet or triplet, whereas the ground state of the odd-numbered chains can be doublet or quartet. We discuss how the 13 C NMR chemical shift absorption is affected by increasing the size and changing the parity of the linear carbon chains. We have found that the J coupling constants between the carbon atoms in the linear chains present a well-defined pattern, in good accordance with our electronic structure calculations. For example, in the -C 4 - units we obtain couplings of 43.8, 114.5, 84.6, 114.5, and 43.8 Hz from one end to the other

Effects of Rashba and Dresselhaus spin-orbit couplings on itinerant ferromagnetism

Science.gov (United States)

Liu, Mengnan; Xu, Liping; Wan, Yong; Yan, Xu

2018-02-01

Based on Stoner model for itinerant ferromagnet, effects of spin-orbit coupling (SOC) on ferromagnetism were investigated at zero temperature. It was found that SOC will enhance the critical ferromagnetic exchange interaction for spontaneous magnetization, and then suppress ferromagnetism. In case of the coexistence of Rashba and Dresselhaus SOCs, the mixture of the two spin-orbit couplings showed stronger suppressed effect on ferromagnetism than only one kind of SOC alone. When the two SOCs mixed with equal magnitude, ferromagnetism in itinerant ferromagnet was suppressed to minimum.

/sup 13/C-/sup 13/C spin-spin coupling constants in structural investigations. II. Conformational structure of vinyl ethers

Energy Technology Data Exchange (ETDEWEB)

Krivdin, L.B.; Shcherbakov, V.V.; Bzhezovskii, V.M.; Kalabin, G.A.

1986-10-10

The /sup 13/C-/sup 13/C spin-spin coupling constants between the carbon nuclei of the vinyl group were measured for a series of vinyl ethers. It was established that the unshared electron pairs of the oxygen atom can make a substantial stereospecific contribution to the direct /sup 13/C-/sup 13/C constants of the adjacent nuclei. The observed effect was used to establish the conformational structure of the compounds.

Diffusion equation and spin drag in spin-polarized transport

DEFF Research Database (Denmark)

Flensberg, Karsten; Jensen, Thomas Stibius; Mortensen, Asger

2001-01-01

We study the role of electron-electron interactions for spin-polarized transport using the Boltzmann equation, and derive a set of coupled transport equations. For spin-polarized transport the electron-electron interactions are important, because they tend to equilibrate the momentum of the two-s...

Boson-mediated quantum spin simulators in transverse fields: X Y model and spin-boson entanglement

Science.gov (United States)

Wall, Michael L.; Safavi-Naini, Arghavan; Rey, Ana Maria

2017-01-01

The coupling of spins to long-wavelength bosonic modes is a prominent means to engineer long-range spin-spin interactions, and has been realized in a variety of platforms, such as atoms in optical cavities and trapped ions. To date, much of the experimental focus has been on the realization of long-range Ising models, but generalizations to other spin models are highly desirable. In this work, we explore a previously unappreciated connection between the realization of an X Y model by off-resonant driving of a single sideband of boson excitation (i.e., a single-beam Mølmer-Sørensen scheme) and a boson-mediated Ising simulator in the presence of a transverse field. In particular, we show that these two schemes have the same effective Hamiltonian in suitably defined rotating frames, and analyze the emergent effective X Y spin model through a truncated Magnus series and numerical simulations. In addition to X Y spin-spin interactions that can be nonperturbatively renormalized from the naive Ising spin-spin coupling constants, we find an effective transverse field that is dependent on the thermal energy of the bosons, as well as other spin-boson couplings that cause spin-boson entanglement not to vanish at any time. In the case of a boson-mediated Ising simulator with transverse field, we discuss the crossover from transverse field Ising-like to X Y -like spin behavior as a function of field strength.

Anisotropic interactions of a single spin and dark-spin spectroscopy in diamond

Science.gov (United States)

Epstein, R. J.; Mendoza, F. M.; Kato, Y. K.; Awschalom, D. D.

2005-11-01

Experiments on single nitrogen-vacancy (N-V) centres in diamond, which include electron spin resonance, Rabi oscillations, single-shot spin readout and two-qubit operations with a nearby13C nuclear spin, show the potential of this spin system for solid-state quantum information processing. Moreover, N-V centre ensembles can have spin-coherence times exceeding 50 μs at room temperature. We have developed an angle-resolved magneto-photoluminescence microscope apparatus to investigate the anisotropic electron-spin interactions of single N-V centres at room temperature. We observe negative peaks in the photoluminescence as a function of both magnetic-field magnitude and angle that are explained by coherent spin precession and anisotropic relaxation at spin-level anti-crossings. In addition, precise field alignment unmasks the resonant coupling to neighbouring `dark' nitrogen spins, otherwise undetected by photoluminescence. These results demonstrate the capability of our spectroscopic technique for measuring small numbers of dark spins by means of a single bright spin under ambient conditions.

Heisenberg coupling constant predicted for molecular magnets with pairwise spin-contamination correction

Energy Technology Data Exchange (ETDEWEB)

Masunov, Artëm E., E-mail: amasunov@ucf.edu [NanoScience Technology Center, Department of Chemistry, and Department of Physics, University of Central Florida, Orlando, FL 32826 (United States); Photochemistry Center RAS, ul. Novatorov 7a, Moscow 119421 (Russian Federation); Gangopadhyay, Shruba [Department of Physics, University of California, Davis, CA 95616 (United States); IBM Almaden Research Center, 650 Harry Road, San Jose, CA 95120 (United States)

2015-12-15

New method to eliminate the spin-contamination in broken symmetry density functional theory (BS DFT) calculations is introduced. Unlike conventional spin-purification correction, this method is based on canonical Natural Orbitals (NO) for each high/low spin coupled electron pair. We derive an expression to extract the energy of the pure singlet state given in terms of energy of BS DFT solution, the occupation number of the bonding NO, and the energy of the higher spin state built on these bonding and antibonding NOs (not self-consistent Kohn–Sham orbitals of the high spin state). Compared to the other spin-contamination correction schemes, spin-correction is applied to each correlated electron pair individually. We investigate two binuclear Mn(IV) molecular magnets using this pairwise correction. While one of the molecules is described by magnetic orbitals strongly localized on the metal centers, and spin gap is accurately predicted by Noodleman and Yamaguchi schemes, for the other one the gap is predicted poorly by these schemes due to strong delocalization of the magnetic orbitals onto the ligands. We show our new correction to yield more accurate results in both cases. - Highlights: • Magnetic orbitails obtained for high and low spin states are not related. • Spin-purification correction becomes inaccurate for delocalized magnetic orbitals. • We use the natural orbitals of the broken symmetry state to build high spin state. • This new correction is made separately for each electron pair. • Our spin-purification correction is more accurate for delocalised magnetic orbitals.

Spin-orbit coupling effects in indium antimonide quantum well structures

Science.gov (United States)

Dedigama, Aruna Ruwan

Indium antimonide (InSb) is a narrow band gap material which has the smallest electron effective mass (0.014m0) and the largest electron Lande g-facture (-51) of all the III-V semiconductors. Spin-orbit effects of III-V semiconductor heterostructures arise from two different inversion asymmetries namely bulk inversion asymmetry (BIA) and structural inversion asymmetry (SIA). BIA is due to the zinc-blende nature of this material which leads to the Dresselhaus spin splitting consisting of both linear and cubic in-plane wave vector terms. As its name implies SIA arises due to the asymmetry of the quantum well structure, this leads to the Rashba spin splitting term which is linear in wave vector. Although InSb has theoretically predicted large Dresselhaus (760 eVA3) and Rashba (523 eA 2) coefficients there has been relatively little experimental investigation of spin-orbit coefficients. Spin-orbit coefficients can be extracted from the beating patterns of Shubnikov--de Haas oscillations (SdH), for material like InSb it is hard to use this method due to the existence of large electron Lande g-facture. Therefore it is essential to use a low field magnetotransport technique such as weak antilocalization to extract spin-orbit parameters for InSb. The main focus of this thesis is to experimentally determine the spin-orbit parameters for both symmetrically and asymmetrically doped InSb/InxAl 1-xSb heterostructures. During this study attempts have been made to tune the Rashba spin-orbit coupling coefficient by using a back gate to change the carrier density of the samples. Dominant phase breaking mechanisms for InSb/InxAl1-xSb heterostructures have been identified by analyzing the temperature dependence of the phase breaking field from weak antilocalization measurements. Finally the strong spin-orbit effects on InSb/InxAl1-xSb heterostructures have been demonstrated with ballistic spin focusing devices.

Dynamical correlation functions of the quadratic coupling spin-Boson model

Science.gov (United States)

Zheng, Da-Chuan; Tong, Ning-Hua

2017-06-01

The spin-boson model with quadratic coupling is studied using the bosonic numerical renormalization group method. We focus on the dynamical auto-correlation functions {C}O(ω ), with the operator \\hat{O} taken as {\\hat{{{σ }}}}x, {\\hat{{{σ }}}}z, and \\hat{X}, respectively. In the weak-coupling regime α qualitatively, showing enhanced dephasing at the spin flip point. Project supported by the National Key Basic Research Program of China (Grant No. 2012CB921704), the National Natural Science Foundation of China (Grant No. 11374362), the Fundamental Research Funds for the Central Universities, China, and the Research Funds of Renmin University of China (Grant No. 15XNLQ03).

Superconductivity in three-dimensional spin-orbit coupled semimetals

Science.gov (United States)

Savary, Lucile; Ruhman, Jonathan; Venderbos, Jörn W. F.; Fu, Liang; Lee, Patrick A.

2017-12-01

Motivated by the experimental detection of superconductivity in the low-carrier density half-Heusler compound YPtBi, we study the pairing instabilities of three-dimensional strongly spin-orbit coupled semimetals with a quadratic band touching point. In these semimetals the electronic structure at the Fermi energy is described by spin j =3/2 quasiparticles, which are fundamentally different from those in ordinary metals with spin j =1/2 . For both local and nonlocal pairing channels in j =3/2 materials we develop a general approach to analyzing pairing instabilities, thereby providing the computational tools needed to investigate the physics of these systems beyond phenomenological considerations. Furthermore, applying our method to a generic density-density interaction, we establish that: (i) The pairing strengths in the different symmetry channels uniquely encode the j =3/2 nature of the Fermi surface band structure—a manifestation of the fundamental difference with ordinary metals. (ii) The leading odd-parity pairing instabilities are different for electron doping and hole doping. Finally, we argue that polar phonons, i.e., Coulomb interactions mediated by the long-ranged electric polarization of the optical phonon modes, provide a coupling strength large enough to account for a Kelvin-range transition temperature in the s -wave channel, and are likely to play an important role in the overall attraction in non-s -wave channels. Moreover, the explicit calculation of the coupling strengths allows us to conclude that the two largest non-s -wave contributions occur in nonlocal channels, in contrast with what has been commonly assumed.

Exploring the Structure of a DNA Hairpin with the Help of NMR Spin-Spin Coupling Constants: An Experimental and Quantum Chemical Investigation

Czech Academy of Sciences Publication Activity Database

Sychrovský, Vladimír; Vacek, Jaroslav; Hobza, Pavel; Žídek, L.; Sklenář, V.; Cremer, D.

2002-01-01

Roč. 106, - (2002), s. 10242-10250 ISSN 1089-5639 R&D Projects: GA MŠk LN00A032 Institutional research plan: CEZ:AV0Z4040901 Keywords : DNA * help of NMR spin-spin coupling constants * quantum chemical investigation Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 2.765, year: 2002

Hybrid quantum circuit with a superconducting qubit coupled to an electron spin ensemble

Energy Technology Data Exchange (ETDEWEB)

Kubo, Yuimaru; Grezes, Cecile; Vion, Denis; Esteve, Daniel; Bertet, Patrice [Quantronics Group, SPEC (CNRS URA 2464), CEA-Saclay, 91191 Gif-sur-Yvette (France); Diniz, Igor; Auffeves, Alexia [Institut Neel, CNRS, BP 166, 38042 Grenoble (France); Isoya, Jun-ichi [Research Center for Knowledge Communities, University of Tsukuba, 305-8550 Tsukuba (Japan); Jacques, Vincent; Dreau, Anais; Roch, Jean-Francois [LPQM (CNRS, UMR 8537), Ecole Normale Superieure de Cachan, 94235 Cachan (France)

2013-07-01

We report the experimental realization of a hybrid quantum circuit combining a superconducting qubit and an ensemble of electronic spins. The qubit, of the transmon type, is coherently coupled to the spin ensemble consisting of nitrogen-vacancy (NV) centers in a diamond crystal via a frequency-tunable superconducting resonator acting as a quantum bus. Using this circuit, we prepare arbitrary superpositions of the qubit states that we store into collective excitations of the spin ensemble and retrieve back into the qubit. We also report a new method for detecting the magnetic resonance of electronic spins at low temperature with a qubit using the hybrid quantum circuit, as well as our recent progress on spin echo experiments.

Higher-spin fields in braneworlds

Energy Technology Data Exchange (ETDEWEB)

Germani, Cristiano [DAMTP, Centre for Mathematical Sciences, University of Cambridge, Wilberforce Road, Cambridge CB3 0WA (United Kingdom)]. E-mail: c.germani@damtp.cam.ac.uk; Kehagias, Alex [Physics Division, National Technical University of Athens, 15780 Zografou Campus, Athens (Greece)]. E-mail: kehagias@central.ntua.gr

2005-10-03

The dynamics of higher-spin fields in braneworlds is discussed. In particular, we study fermionic and bosonic higher-spin fields in AdS{sub 5} and their localization on branes. We find that four-dimensional zero modes exist only for spin-one fields, if there are no couplings to the boundaries. If boundary couplings are allowed, as in the case of the bulk graviton, all bosons acquire a zero mode irrespective of their spin. We show that there are boundary conditions for fermions, which generate chiral zero modes in the four-dimensional spectrum. We also propose a gauge invariant on-shell action with cubic interactions by adding non-minimal couplings, which depend on the Weyl tensor. In addition, consistent couplings between higher-spin fields and matter on the brane are presented. Finally, in the AdS/CFT correspondence, where bulk 5D theories on AdS are related to 4D CFTs, we explicitly discuss the holographic picture of higher-spin theories in AdS{sub 5} with and without boundaries.

Extrinsic spin Hall effect in graphene

Science.gov (United States)

Rappoport, Tatiana

The intrinsic spin-orbit coupling in graphene is extremely weak, making it a promising spin conductor for spintronic devices. In addition, many applications also require the generation of spin currents in graphene. Theoretical predictions and recent experimental results suggest one can engineer the spin Hall effect in graphene by greatly enhancing the spin-orbit coupling in the vicinity of an impurity. The extrinsic spin Hall effect then results from the spin-dependent skew scattering of electrons by impurities in the presence of spin-orbit interaction. This effect can be used to efficiently convert charge currents into spin-polarized currents. I will discuss recent experimental results on spin Hall effect in graphene decorated with adatoms and metallic cluster and show that a large spin Hall effect can appear due to skew scattering. While this spin-orbit coupling is small if compared with what it is found in metals, the effect is strongly enhanced in the presence of resonant scattering, giving rise to robust spin Hall angles. I will present our single impurity scattering calculations done with exact partial-wave expansions and complement the analysis with numerical results from a novel real-space implementation of the Kubo formalism for tight-binding Hamiltonians. The author acknowledges the Brazilian agencies CNPq, CAPES, FAPERJ and INCT de Nanoestruturas de Carbono for financial support.

Ab initio theory of spin-orbit coupling for quantum bits in diamond exhibiting dynamic Jahn-Teller effect

Science.gov (United States)

Gali, Adam; Thiering, Gergő

Dopants in solids are promising candidates for implementations of quantum bits for quantum computing. In particular, the high-spin negatively charged nitrogen-vacancy defect (NV) in diamond has become a leading contender in solid-state quantum information processing. The initialization and readout of the spin is based on the spin-selective decay of the photo-excited electron to the ground state which is mediated by spin-orbit coupling between excited states states and phonons. Generally, the spin-orbit coupling plays a crucial role in the optical spinpolarization and readout of NV quantum bit (qubit) and alike. Strong electron-phonon coupling in dynamic Jahn-Teller (DJT) systems can substantially influence the effective strength of spin-orbit coupling. Here we show by ab initio supercell density functional theory (DFT) calculations that the intrinsic spin-orbit coupling is strongly damped by DJT effect in the triplet excited state that has a consequence on the rate of non-radiative decay. This theory is applied to the ground state of silicon-vacancy (SiV) and germanium-vacancy (GeV) centers in their negatively charged state that can also act like qubits. We show that the intrinsic spin-orbit coupling in SiV and GeV centers is in the 100 GHz region, in contrast to the NV center of 10 GHz region. Our results provide deep insight in the nature of SiV and GeV qubits in diamond. EU FP7 DIADEMS project (Contract No. 611143).

Internal Spin Control, Squeezing and Decoherence in Ensembles of Alkali Atomic Spins

Science.gov (United States)

Norris, Leigh Morgan

Large atomic ensembles interacting with light are one of the most promising platforms for quantum information processing. In the past decade, novel applications for these systems have emerged in quantum communication, quantum computing, and metrology. Essential to all of these applications is the controllability of the atomic ensemble, which is facilitated by a strong coupling between the atoms and light. Non-classical spin squeezed states are a crucial step in attaining greater ensemble control. The degree of entanglement present in these states, furthermore, serves as a benchmark for the strength of the atom-light interaction. Outside the broader context of quantum information processing with atomic ensembles, spin squeezed states have applications in metrology, where their quantum correlations can be harnessed to improve the precision of magnetometers and atomic clocks. This dissertation focuses upon the production of spin squeezed states in large ensembles of cold trapped alkali atoms interacting with optical fields. While most treatments of spin squeezing consider only the case in which the ensemble is composed of two level systems or qubits, we utilize the entire ground manifold of an alkali atom with hyperfine spin f greater than or equal to 1/2, a qudit. Spin squeezing requires non-classical correlations between the constituent atomic spins, which are generated through the atoms' collective coupling to the light. Either through measurement or multiple interactions with the atoms, the light mediates an entangling interaction that produces quantum correlations. Because the spin squeezing treated in this dissertation ultimately originates from the coupling between the light and atoms, conventional approaches of improving this squeezing have focused on increasing the optical density of the ensemble. The greater number of internal degrees of freedom and the controllability of the spin-f ground hyperfine manifold enable novel methods of enhancing squeezing. In

Calculations of spin-polarized Goos-Hänchen displacement in magnetically confined GaAs/Al x Ga1-x As nanostructure modulated by spin-orbit couplings

Science.gov (United States)

Lu, Mao-Wang; Chen, Sai-Yan; Zhang, Gui-Lian; Huang, Xin-Hong

2018-04-01

We theoretically investigate Goos-Hänchen (GH) displacement by modelling the spin transport in an archetypal device structure—a magnetically confined GaAs/Al x Ga1-x As nanostructure modulated by spin-orbit coupling (SOC). Both Rashba and Dresselhaus SOCs are taken into account. The degree of spin-polarized GH displacement can be tuned by Rashba or Dresselhaus SOC, i.e. interfacial confining electric field or strain engineering. Based on such a semiconductor nanostructure, a controllable spatial spin splitter can be proposed for spintronics applications.

Calculations of spin-polarized Goos-Hänchen displacement in magnetically confined GaAs/Al x Ga1-x As nanostructure modulated by spin-orbit couplings.

Science.gov (United States)

Lu, Mao-Wang; Chen, Sai-Yan; Zhang, Gui-Lian; Huang, Xin-Hong

2018-04-11

We theoretically investigate Goos-Hänchen (GH) displacement by modelling the spin transport in an archetypal device structure-a magnetically confined GaAs/Al x Ga 1-x As nanostructure modulated by spin-orbit coupling (SOC). Both Rashba and Dresselhaus SOCs are taken into account. The degree of spin-polarized GH displacement can be tuned by Rashba or Dresselhaus SOC, i.e. interfacial confining electric field or strain engineering. Based on such a semiconductor nanostructure, a controllable spatial spin splitter can be proposed for spintronics applications.

Tunable spin-orbit coupling for ultracold atoms in two-dimensional optical lattices

Science.gov (United States)

Grusdt, Fabian; Li, Tracy; Bloch, Immanuel; Demler, Eugene

2017-06-01

Spin-orbit coupling (SOC) is at the heart of many exotic band structures and can give rise to many-body states with topological order. Here we present a general scheme based on a combination of microwave driving and lattice shaking for the realization of two-dimensional SOC with ultracold atoms in systems with inversion symmetry. We show that the strengths of Rashba and Dresselhaus SOC can be independently tuned in a spin-dependent square lattice. More generally, our method can be used to open gaps between different spin states without breaking time-reversal symmetry. We demonstrate that this allows for the realization of topological insulators with nontrivial spin textures closely related to the Kane-Mele model.

Excitation spectrum of Heisenberg spin ladders

International Nuclear Information System (INIS)

Barnes, T.; Dagotto, E.; Riera, J.; Swanson, E.S.

1993-01-01

Heisenberg antiferromagnetic spin ''ladders'' (two coupled spin chains) are low-dimensional magnetic systems which for S=1/2 interpolate between half-integer-spin chains, when the chains are decoupled, and effective integer-spin one-dimensional chains in the strong-coupling limit. The spin-1/2 ladder may be realized in nature by vanadyl pyrophosphate, (VO) 2 P 2 O 7 . In this paper we apply strong-coupling perturbation theory, spin-wave theory, Lanczos techniques, and a Monte Carlo method to determine the ground-state energy and the low-lying excitation spectrum of the ladder. We find evidence of a nonzero spin gap for all interchain couplings J perpendicular >0. A band of spin-triplet excitations above the gap is also analyzed. These excitations are unusual for an antiferromagnet, since their long-wavelength dispersion relation behaves as (k-k 0 ) 2 (in the strong-coupling limit J perpendicular much-gt J, where J is the in-chain antiferromagnetic coupling). Their band is folded, with a minimum energy at k 0 =π, and a maximum between k 1 =π/2 (for J perpendicular =0) and 0 (for J perpendicular =∞). We also give numerical results for the dynamical structure factor S(q,ω), which can be determined in neutron scattering experiments. Finally, possible experimental techniques for studying the excitation spectrum are discussed

Entanglement purification and concentration of electron-spin entangled states using quantum-dot spins in optical microcavities

International Nuclear Information System (INIS)

Wang Chuan; Zhang Yong; Jin Guangsheng

2011-01-01

We present an entanglement purification protocol and an entanglement concentration protocol for electron-spin entangled states, resorting to quantum-dot spin and optical-microcavity-coupled systems. The parity-check gates (PCGs) constructed by the cavity-spin-coupling system provide a different method for the entanglement purification of electron-spin entangled states. This protocol can efficiently purify an electron ensemble in a mixed entangled state. The PCGs can also concentrate electron-spin pairs in less-entangled pure states efficiently. The proposed methods are more flexible as only single-photon detection and single-electron detection are needed.

Spin-lattice relaxation of individual solid-state spins

Science.gov (United States)

Norambuena, A.; Muñoz, E.; Dinani, H. T.; Jarmola, A.; Maletinsky, P.; Budker, D.; Maze, J. R.

2018-03-01

Understanding the effect of vibrations on the relaxation process of individual spins is crucial for implementing nanosystems for quantum information and quantum metrology applications. In this work, we present a theoretical microscopic model to describe the spin-lattice relaxation of individual electronic spins associated to negatively charged nitrogen-vacancy centers in diamond, although our results can be extended to other spin-boson systems. Starting from a general spin-lattice interaction Hamiltonian, we provide a detailed description and solution of the quantum master equation of an electronic spin-one system coupled to a phononic bath in thermal equilibrium. Special attention is given to the dynamics of one-phonon processes below 1 K where our results agree with recent experimental findings and analytically describe the temperature and magnetic-field scaling. At higher temperatures, linear and second-order terms in the interaction Hamiltonian are considered and the temperature scaling is discussed for acoustic and quasilocalized phonons when appropriate. Our results, in addition to confirming a T5 temperature dependence of the longitudinal relaxation rate at higher temperatures, in agreement with experimental observations, provide a theoretical background for modeling the spin-lattice relaxation at a wide range of temperatures where different temperature scalings might be expected.

Robust adiabatic approach to optical spin entangling in coupled quantum dots

International Nuclear Information System (INIS)

Gauger, Erik M; Benjamin, Simon C; Lovett, Brendon W; Nazir, Ahsan; Stace, Thomas M

2008-01-01

Excitonic transitions offer a possible route to ultrafast optical spin manipulation in coupled nanostructures. We perform here a detailed study of the three principal exciton-mediated decoherence channels for optically controlled electron spin qubits in coupled quantum dots: radiative decay of the excitonic state, exciton-phonon interactions, and Landau-Zener transitions between laser-dressed states. We consider a scheme for producing an entangling controlled-phase gate on a pair of coupled spins which, in its simplest dynamic form, renders the system subject to fast decoherence rates associated with exciton creation during the gating operation. In contrast, we show that an adiabatic approach employing off-resonant laser excitation allows us to suppress all sources of decoherence simultaneously, significantly increasing the fidelity of operations at only a relatively small gating time cost. We find that controlled-phase gates accurate to one part in 10 2 can realistically be achieved with the adiabatic approach, whereas the conventional dynamic approach does not appear to support a fidelity suitable for scalable quantum computation. Our predictions could be demonstrated experimentally in the near future

Universal relations for spin-orbit-coupled Fermi gas near an s -wave resonance

Science.gov (United States)

Zhang, Pengfei; Sun, Ning

2018-04-01

Synthetic spin-orbit-coupled quantum gases have been widely studied both experimentally and theoretically in the past decade. As shown in previous studies, this modification of single-body dispersion will in general couple different partial waves of the two-body scattering and thus distort the wave function of few-body bound states which determines the short-distance behavior of many-body wave function. In this work, we focus on the two-component Fermi gas with one-dimensional or three-dimensional spin-orbit coupling (SOC) near an s -wave resonance. Using the method of effective field theory and the operator product expansion, we derive universal relations for both systems, including the adiabatic theorem, viral theorem, and pressure relation, and obtain the momentum distribution matrix 〈ψa†(q ) ψb(q ) 〉 at large q (a ,b are spin indices). The momentum distribution matrix shows both spin-dependent and spatial anisotropic features. And the large momentum tail is modified at the subleading order thanks to the SOC. We also discuss the experimental implication of these results depending on the realization of the SOC.

Collapse and revival of entanglement between qubits coupled to a spin coherent state

Science.gov (United States)

Bahari, Iskandar; Spiller, Timothy P.; Dooley, Shane; Hayes, Anthony; McCrossan, Francis

We extend the study of the Jayne-Cummings (JC) model involving a pair of identical two-level atoms (or qubits) interacting with a single mode quantized field. We investigate the effects of replacing the radiation field mode with a composite spin, comprising N qubits, or spin-1/2 particles. This model is relevant for physical implementations in superconducting circuit QED, ion trap and molecular systems. For the case of the composite spin prepared in a spin coherent state, we demonstrate the similarities of this set-up to the qubits-field model in terms of the time evolution, attractor states and in particular the collapse and revival of the entanglement between the two qubits. We extend our analysis by taking into account an effect due to qubit imperfections. We consider a difference (or “mismatch”) in the dipole interaction strengths of the two qubits, for both the field mode and composite spin cases. To address decoherence due to this mismatch, we then average over this coupling strength difference with distributions of varying width. We demonstrate in both the field mode and the composite spin scenarios that increasing the width of the “error” distribution increases suppression of the coherent dynamics of the coupled system, including the collapse and revival of the entanglement between the qubits.

Circuit quantum electrodynamics with a spin qubit.

Science.gov (United States)

Petersson, K D; McFaul, L W; Schroer, M D; Jung, M; Taylor, J M; Houck, A A; Petta, J R

2012-10-18

Electron spins trapped in quantum dots have been proposed as basic building blocks of a future quantum processor. Although fast, 180-picosecond, two-quantum-bit (two-qubit) operations can be realized using nearest-neighbour exchange coupling, a scalable, spin-based quantum computing architecture will almost certainly require long-range qubit interactions. Circuit quantum electrodynamics (cQED) allows spatially separated superconducting qubits to interact via a superconducting microwave cavity that acts as a 'quantum bus', making possible two-qubit entanglement and the implementation of simple quantum algorithms. Here we combine the cQED architecture with spin qubits by coupling an indium arsenide nanowire double quantum dot to a superconducting cavity. The architecture allows us to achieve a charge-cavity coupling rate of about 30 megahertz, consistent with coupling rates obtained in gallium arsenide quantum dots. Furthermore, the strong spin-orbit interaction of indium arsenide allows us to drive spin rotations electrically with a local gate electrode, and the charge-cavity interaction provides a measurement of the resulting spin dynamics. Our results demonstrate how the cQED architecture can be used as a sensitive probe of single-spin physics and that a spin-cavity coupling rate of about one megahertz is feasible, presenting the possibility of long-range spin coupling via superconducting microwave cavities.

Shot noise of spin current and spin transfer torque

Science.gov (United States)

Yu, Yunjin; Zhan, Hongxin; Wan, Langhui; Wang, Bin; Wei, Yadong; Sun, Qingfeng; Wang, Jian

2013-04-01

We report the theoretical investigation of the shot noise of the spin current (Sσ) and the spin transfer torque (Sτ) for non-collinear spin polarized transport in a spin-valve device which consists of a normal scattering region connected by two ferromagnetic electrodes (MNM system). Our theory was developed using the non-equilibrium Green’s function method, and general nonlinear Sσ - V and Sτ - V relations were derived as a function of the angle θ between the magnetizations of two leads. We have applied our theory to a quantum dot system with a resonant level coupled with two ferromagnetic electrodes. It was found that, for the MNM system, the auto-correlation of the spin current is enough to characterize the fluctuation of the spin current. For a system with three ferromagnetic layers, however, both auto-correlation and cross-correlation of the spin current are needed to characterize the noise of the spin current. For a quantum dot with a resonant level, the derivative of spin torque with respect to bias voltage is proportional to sinθ when the system is far away from resonance. When the system is near resonance, the spin transfer torque becomes a non-sinusoidal function of θ. The derivative of the noise of the spin transfer torque with respect to the bias voltage Nτ behaves differently when the system is near or far away from resonance. Specifically, the differential shot noise of the spin transfer torque Nτ is a concave function of θ near resonance while it becomes a convex function of θ far away from resonance. For certain bias voltages, the period Nτ(θ) becomes π instead of 2π. For small θ, it was found that the differential shot noise of the spin transfer torque is very sensitive to the bias voltage and the other system parameters.

Spin relaxation through Kondo scattering in Cu/Py lateral spin valves

Science.gov (United States)

Batley, J. T.; Rosaond, M. C.; Ali, M.; Linfield, E. H.; Burnell, G.; Hickey, B. J.

Within non-magnetic metals it is reasonable to expect the Elliot-Yafet mechanism to govern spin-relaxation and thus the temperature dependence of the spin diffusion length might be inversely proportional to resistivity. However, in lateral spin valves, measurements have found that at low temperatures the spin diffusion length unexpectedly decreases. We have fabricated lateral spin valves from Cu with different concentrations of magnetic impurities. Through temperature dependent charge and spin transport measurements we present clear evidence linking the presence of the Kondo effect within Cu to the suppression of the spin diffusion length below 30 K. We have calculated the spin-relaxation rate and isolated the contribution from magnetic impurities. At very low temperatures electron-electron interactions play a more prominent role in the Kondo effect. Well below the Kondo temperature a strong-coupling regime exists, where the moments become screened and the magnetic dephasing rate is reduced. We also investigate the effect of this low temperature regime (>1 K) on a pure spin current. This work shows the dominant role of Kondo scattering, even in low concentrations of order 1 ppm, within pure spin transport.

A possible interaction between spin-1/2 and spin-3/2 fields

International Nuclear Information System (INIS)

Fleury, N.; Lopes, J.L.

1984-01-01

A straighforward extension of the standard Weinberg-Salam model to Rarita-Schwinger formalism, is a heuristic way to obtain electroweak currents for spin-3/2 leptons. A new interaction between spin-1/2 and spin-3/2 particles that maintains the SU(2) x U(1) gauge invariance is postulated and a possible form for the interaction involving these two types of particles and the gauge fields is obtained. This takes place through a coupling which involves derivatives of the electromagnetic field and the corresponding coupling constant is inversely proportional to the mass of spin-3/2 particles. Several reactions are possible with this new interaction such as the radiative decay of a charged Rarita-Schwinger particle. Other reactions are corrections to well-known processes: for instance, in the usual Compton effect, the fermionic virtual line can be replaced by the corresponding spin-3/2 one. But, due to the large mass of the spin-3/2 lepton, these corrections are significantly non negligible only at ultra relativistic energies. On the other hand, in the low energy limit this correction gives fortunately no contribution to the Thomson cross section because the coupling 3/2 - 1/2 - γ is proportional to the photon's momentum. If it is considered all the possible couplings of these fields, one can combine them in diagrams of lowest orders whose theoretical predictions have to be submitted to experimental pressure. (Author) [pt

A possible interaction between spin-1/2 and spin-3/2 fields

International Nuclear Information System (INIS)

Fleury, N.; Leite Lopes, J.

1984-01-01

A straightforward extension of the standard Weinberg-Salam model to Rarita-Schwinger formalism, is a heuristic way to obtain electroweak currents for spin-3/2 leptons. We postulate a new interaction between spin-1/2 and spin-3/2 particles that maintains the SU(2) x U(1) gauge invariance, and we obtain a possible form for the interaction involving these two types of particles and the gauge fields. This takes place through a coupling which involves derivatives of the electromagnetic field and the corresponding coupling constant is inversely proportional to the mass of spin-3/2 particles. Several reactions are possible with this new interaction such as the radiative decay of a charged Rarita-Schwinger particle. Other reactions are corrections to well-known processes: for instance, in the usual Compton effect, the fermionic virtual line can be replaced by the corresponding spin-3/2 one. But, due to the large mass of the spin-3/2 lepton, these corrections are significantly non negligible only at ultra relativistic energies. On the other hand, in the low energy limit this correction gives fortunately no contribution to the Thomson cross section because the coupling 3/2-1/2-γ is proportional to the photon's momentum. If one considers all the possible couplings of these fields, one can combine them in diagrams of lowest orders whose theoretical predictions have to be submitted to experimental pressure

Spin inelastic electron tunneling spectroscopy on local spin adsorbed on surface.

Science.gov (United States)

Fransson, J

2009-06-01

The recent experimental conductance measurements taken on magnetic impurities on metallic surfaces, using scanning tunneling microscopy technique and suggesting occurrence of inelastic scattering processes, are theoretically addressed. We argue that the observed conductance signatures are caused by transitions between the spin states that have opened due to, for example, exchange coupling between the local spins and the tunneling electrons, and are directly interpretable in terms of inelastic transitions energies. Feasible measurements using spin-polarized scanning tunneling microscopy that would enable new information about the excitation spectrum of the local spins are discussed.

Spin-orbit coupling and the static polarizability of single-wall carbon nanotubes

International Nuclear Information System (INIS)

Diniz, Ginetom S.; Ulloa, Sergio E.

2014-01-01

We calculate the static longitudinal polarizability of single-wall carbon tubes in the long wavelength limit taking into account spin-orbit effects. We use a four-orbital orthogonal tight-binding formalism to describe the electronic states and the random phase approximation to calculate the dielectric function. We study the role of both the Rashba as well as the intrinsic spin-orbit interactions on the longitudinal dielectric response, i.e., when the probing electric field is parallel to the nanotube axis. The spin-orbit interaction modifies the nanotube electronic band dispersions, which may especially result in a small gap opening in otherwise metallic tubes. The bandgap size and state features, the result of competition between Rashba and intrinsic spin-orbit interactions, result in drastic changes in the longitudinal static polarizability of the system. We discuss results for different nanotube types and the dependence on nanotube radius and spin-orbit couplings.

Spin-orbit coupling and the static polarizability of single-wall carbon nanotubes

Energy Technology Data Exchange (ETDEWEB)

Diniz, Ginetom S., E-mail: ginetom@gmail.com; Ulloa, Sergio E. [Department of Physics and Astronomy and Nanoscale and Quantum Phenomena Institute, Ohio University, Athens, Ohio 45701-2979 (United States)

2014-07-14

We calculate the static longitudinal polarizability of single-wall carbon tubes in the long wavelength limit taking into account spin-orbit effects. We use a four-orbital orthogonal tight-binding formalism to describe the electronic states and the random phase approximation to calculate the dielectric function. We study the role of both the Rashba as well as the intrinsic spin-orbit interactions on the longitudinal dielectric response, i.e., when the probing electric field is parallel to the nanotube axis. The spin-orbit interaction modifies the nanotube electronic band dispersions, which may especially result in a small gap opening in otherwise metallic tubes. The bandgap size and state features, the result of competition between Rashba and intrinsic spin-orbit interactions, result in drastic changes in the longitudinal static polarizability of the system. We discuss results for different nanotube types and the dependence on nanotube radius and spin-orbit couplings.

Universal Borromean Binding in Spin-Orbit-Coupled Ultracold Fermi Gases

Directory of Open Access Journals (Sweden)

Xiaoling Cui

2014-08-01

Full Text Available Borromean rings and Borromean binding, a class of intriguing phenomena as three objects are linked (bound together while any two of them are unlinked (unbound, widely exist in nature and have been found in systems of biology, chemistry, and physics. Previous studies have suggested that the occurrence of such a binding in physical systems typically relies on the microscopic details of pairwise interaction potentials at short range and is, therefore, nonuniversal. Here, we report a new type of Borromean binding in ultracold Fermi gases with Rashba spin-orbit coupling, which is universal against short-range interaction details, with its binding energy only dependent on the s-wave scattering length and the spin-orbit-coupling strength. We show that the occurrence of this universal Borromean binding is facilitated by the symmetry of the single-particle dispersion under spin-orbit coupling and is, therefore, symmetry selective rather than interaction selective. The state is robust over a wide range of mass ratios between composing fermions, which are accessible by Li-Li, K-K, and K-Li mixtures in cold-atom experiments. Our results reveal the importance of single- particle spectral symmetry in few-body physics and shed light on the emergence of new quantum phases in a many-body system with exotic few-body correlations.

Full counting statistics in a serially coupled double quantum dot system with spin-orbit coupling

Science.gov (United States)

Wang, Qiang; Xue, Hai-Bin; Xie, Hai-Qing

2018-04-01

We study the full counting statistics of electron transport through a serially coupled double quantum dot (QD) system with spin-orbit coupling (SOC) weakly coupled to two electrodes. We demonstrate that the spin polarizations of the source and drain electrodes determine whether the shot noise maintains super-Poissonian distribution, and whether the sign transitions of the skewness from positive to negative values and of the kurtosis from negative to positive values take place. In particular, the interplay between the spin polarizations of the source and drain electrodes and the magnitude of the external magnetic field, can give rise to a gate-voltage-tunable strong negative differential conductance (NDC) and the shot noise in this NDC region is significantly enhanced. Importantly, for a given SOC parameter, the obvious variation of the high-order current cumulants as a function of the energy-level detuning in a certain range, especially the dip position of the Fano factor of the skewness can be used to qualitatively extract the information about the magnitude of the SOC.

Ultrafast demagnetization in rare-earth alloys: the role of spin-orbit coupling

Energy Technology Data Exchange (ETDEWEB)

Le Guyader, Loic; Solopow, Sergej; Radu, Florin; Holldack, Karsten; Mitzner, Rolf; Kachel, Torsten; Pontius, Niko; Foehlisch, Alexander; Radu, Ilie [Helmholtz-Zentrum Berlin fuer Materialien und Energie GmbH, Berlin (Germany); Abrudan, Radu [Helmholtz-Zentrum Berlin fuer Materialien und Energie GmbH, Berlin (Germany); Institut fuer Experimentalphysik/Festkoerperphysik, Ruhr-Universitaet Bochum (Germany)

2015-07-01

Understanding the ultrafast demagnetization occurring upon femtosecond laser excitation of a magnetic material is a fundamental problem of modern magnetism and its microscopic origin remains highly elusive and intensely debated. Particularly, the spin-orbit coupling mediating the spin-lattice interaction is one of the key ingredients. An intriguing case of tunable parallel to anti-parallel LS coupling can be realized in rare-earth (RE) alloys. For instance, Gd60Sm40 and Gd60Dy40 alloys have similar absolute S and L, but exhibit opposite LS coupling while displaying the same ferromagnetic ordering temperature of 250 K. They constitute thus an ideal case to investigate the particular role of the LS coupling on the ultrafast demagnetization. Here we report on the properties of such RE thin film alloys using X-ray Magnetic Circular Dichroism (XMCD) with the spin and orbit sum rules at M5,4 edges. Femtosecond time-resolved transmission XMCD measurements performed at the slicing beamline reveal the element-specific demagnetization time constant in these alloys. Funding from European Union through FEMTOSPIN is gratefully acknowledged.

Spin-Triplet Pairing Induced by Spin-Singlet Interactions in Noncentrosymmetric Superconductors

Science.gov (United States)

Matsuzaki, Tomoaki; Shimahara, Hiroshi

2017-02-01

In noncentrosymmetric superconductors, we examine the effect of the difference between the intraband and interband interactions, which becomes more important when the band splitting increases. We define the difference ΔVμ between their coupling constants, i.e., that between the intraband and interband hopping energies of intraband Cooper pairs. Here, the subscript μ of ΔVμ indicates that the interactions scatter the spin-singlet and spin-triplet pairs when μ = 0 and μ = 1,2,3, respectively. It is shown that the strong antisymmetric spin-orbit interaction reverses the target spin parity of the interaction: it converts the spin-singlet and spin-triplet interactions represented by ΔV0 and ΔVμ>0 into effective spin-triplet and spin-singlet pairing interactions, respectively. Hence, for example, triplet pairing can be induced solely by the singlet interaction ΔV0. We name the pairing symmetry of the system after that of the intraband Cooper pair wave function, but with an odd-parity phase factor excluded. The pairing symmetry must then be even, even for the triplet component, and the following results are obtained. When ΔVμ is small, the spin-triplet p-wave interactions induce spin-triplet s-wave and spin-triplet d-wave pairings in the regions where the repulsive singlet s-wave interaction is weak and strong, respectively. When ΔV0 is large, a repulsive interband spin-singlet interaction can stabilize spin-triplet pairing. When the Rashba interaction is adopted for the spin-orbit interaction, the spin-triplet pairing interactions mediated by transverse magnetic fluctuations do not contribute to triplet pairing.

Coherent control of two individual electron spins and influence of hyperfine coupling in a double quantum dot

International Nuclear Information System (INIS)

Tarucha, S; Obata, T; Pioro-Ladriere, M; Brunner, R; Shin, Y-S; Kubo, T; Tokura, Y

2011-01-01

Electric dipole spin resonance of two individual electrons and the influence of hyperfine coupling on the spin resonance are studied for a double quantum dot equipped with a micro-magnet. The spin resonance occurs by oscillating the electron in each dot at microwave (MW) frequencies in the presence of a micro-magnet induced stray field. The observed continuous wave (CW) and time-resolved spin resonances are consistent with calculations in which the MW induced AC electric field and micro-magnet induced stray field are taken into account. The influence of hyperfine coupling causes an increase and broadening of the respective CW spin resonance peaks through dynamical nuclear polarization when sweeping up the magnetic field. This behaviour appears stronger for the larger of the two spin resonance peaks and in general becomes more pronounced as the MW power increases, both reflecting that the electron-nuclei interaction is more efficient for the stronger spin resonance. In addition the hyperfine coupling effect only becomes pronounced when the MW induced AC magnetic field exceeds the fluctuating nuclear field.

Topological phase transition in anisotropic square-octagon lattice with spin-orbit coupling and exchange field

Science.gov (United States)

Yang, Yuan; Yang, Jian; Li, Xiaobing; Zhao, Yue

2018-03-01

We investigate the topological phase transitions in an anisotropic square-octagon lattice in the presence of spin-orbit coupling and exchange field. On the basis of the Chern number and spin Chern number, we find a number of topologically distinct phases with tuning the exchange field, including time-reversal-symmetry-broken quantum spin Hall phases, quantum anomalous Hall phases and a topologically trivial phase. Particularly, we observe a coexistent state of both the quantum spin Hall effect and quantum anomalous Hall effect. Besides, by adjusting the exchange filed, we find the phase transition from time-reversal-symmetry-broken quantum spin Hall phase to spin-imbalanced and spin-polarized quantum anomalous Hall phases, providing an opportunity for quantum spin manipulation. The bulk band gap closes when topological phase transitions occur between different topological phases. Furthermore, the energy and spin spectra of the edge states corresponding to different topological phases are consistent with the topological characterization based on the Chern and spin Chern numbers.

Bipolar spintronics: from spin injection to spin-controlled logic

International Nuclear Information System (INIS)

Zutic, Igor; Fabian, Jaroslav; Erwin, Steven C

2007-01-01

An impressive success of spintronic applications has been typically realized in metal-based structures which utilize magnetoresistive effects for substantial improvements in the performance of computer hard drives and magnetic random access memories. Correspondingly, the theoretical understanding of spin-polarized transport is usually limited to a metallic regime in a linear response, which, while providing a good description for data storage and magnetic memory devices, is not sufficient for signal processing and digital logic. In contrast, much less is known about possible applications of semiconductor-based spintronics and spin-polarized transport in related structures which could utilize strong intrinsic nonlinearities in current-voltage characteristics to implement spin-based logic. Here we discuss the challenges for realizing a particular class of structures in semiconductor spintronics: our proposal for bipolar spintronic devices in which carriers of both polarities (electrons and holes) contribute to spin-charge coupling. We formulate the theoretical framework for bipolar spin-polarized transport, and describe several novel effects in two- and three-terminal structures which arise from the interplay between nonequilibrium spin and equilibrium magnetization

Equations of motion for massive spin 2 field coupled to gravity

International Nuclear Information System (INIS)

Buchbinder, I.L.; Gitman, D.M.; Krykhtin, V.A.; Pershin, V.D.

2000-01-01

We investigate the problems of consistency and causality for the equations of motion describing massive spin two field in external gravitational and massless scalar dilaton fields in arbitrary spacetime dimension. From the field theoretical point of view we consider a general classical action with non-minimal couplings and find gravitational and dilaton background on which this action describes a theory consistent with the flat space limit. In the case of pure gravitational background all field components propagate causally. We show also that the massive spin two field can be consistently described in arbitrary background by means of the lagrangian representing an infinite series in the inverse mass. Within string theory we obtain equations of motion for the massive spin two field coupled to gravity from the requirement of quantum Weyl invariance of the corresponding two-dimensional sigma-model. In the lowest order in α' we demonstrate that these effective equations of motion coincide with consistent equations derived in field theory

Equations of motion for massive spin 2 field coupled to gravity

Energy Technology Data Exchange (ETDEWEB)

Buchbinder, I.L. E-mail: ilb@mail.tomsknet.ru; Gitman, D.M. E-mail: gitman@fma.if.usp.br; Krykhtin, V.A. E-mail: krykhtin@phys.dfe.tpu.edu.ru; Pershin, V.D. E-mail: pershin@ic.tsu.ru

2000-09-18

We investigate the problems of consistency and causality for the equations of motion describing massive spin two field in external gravitational and massless scalar dilaton fields in arbitrary spacetime dimension. From the field theoretical point of view we consider a general classical action with non-minimal couplings and find gravitational and dilaton background on which this action describes a theory consistent with the flat space limit. In the case of pure gravitational background all field components propagate causally. We show also that the massive spin two field can be consistently described in arbitrary background by means of the lagrangian representing an infinite series in the inverse mass. Within string theory we obtain equations of motion for the massive spin two field coupled to gravity from the requirement of quantum Weyl invariance of the corresponding two-dimensional sigma-model. In the lowest order in {alpha}' we demonstrate that these effective equations of motion coincide with consistent equations derived in field theory.

High frequency spin torque oscillators with composite free layer spin valve

International Nuclear Information System (INIS)

Natarajan, Kanimozhi; Arumugam, Brinda; Rajamani, Amuda

2016-01-01

We report the oscillations of magnetic spin components in a composite free layer spin valve. The associated Landau–Lifshitz–Gilbert–Slonczewski (LLGS) equation is studied by stereographically projecting the spin on to a complex plane and the spin components were found. A fourth order Runge–Kutta numerical integration on LLGS equation also confirms the similar trajectories of the spin components. This study establishes the possibility of a Spin Torque Oscillator in a composite free layer spin valve, where the exchange coupling is ferromagnetic in nature. In-plane and out-of-plane precessional modes of magnetization oscillations were found in zero applied magnetic field and the frequencies of the oscillations were calculated from Fast Fourier Transform of the components of magnetization. Behavior of Power Spectral Density for a range of current density is studied. Finally our analysis shows the occurrence of highest frequency 150 GHz, which is in the second harmonics for the specific choice of system parameters.

High frequency spin torque oscillators with composite free layer spin valve

Energy Technology Data Exchange (ETDEWEB)

Natarajan, Kanimozhi; Arumugam, Brinda; Rajamani, Amuda

2016-07-15

We report the oscillations of magnetic spin components in a composite free layer spin valve. The associated Landau–Lifshitz–Gilbert–Slonczewski (LLGS) equation is studied by stereographically projecting the spin on to a complex plane and the spin components were found. A fourth order Runge–Kutta numerical integration on LLGS equation also confirms the similar trajectories of the spin components. This study establishes the possibility of a Spin Torque Oscillator in a composite free layer spin valve, where the exchange coupling is ferromagnetic in nature. In-plane and out-of-plane precessional modes of magnetization oscillations were found in zero applied magnetic field and the frequencies of the oscillations were calculated from Fast Fourier Transform of the components of magnetization. Behavior of Power Spectral Density for a range of current density is studied. Finally our analysis shows the occurrence of highest frequency 150 GHz, which is in the second harmonics for the specific choice of system parameters.

Constraints on long-range spin-gravity and monopole-dipole couplings of the proton

Science.gov (United States)

Jackson Kimball, Derek F.; Dudley, Jordan; Li, Yan; Patel, Dilan; Valdez, Julian

2017-10-01

Results of a search for a long-range monopole-dipole coupling between the mass of the Earth and rubidium (Rb) nuclear spins are reported. The experiment simultaneously measures the spin precession frequencies of overlapping ensembles of 85Rb and 87Rb atoms contained within an evacuated, antirelaxation-coated vapor cell. The nuclear structure of the Rb isotopes makes the experiment particularly sensitive to spin-dependent interactions of the proton. The spin-dependent component of the gravitational energy of the proton in the Earth's field is found to be smaller than 3 ×10-18 eV , improving laboratory constraints on long-range monopole-dipole interactions by over 3 orders of magnitude.

Spin-polarized spin-orbit-split quantum-well states in a metal film

Energy Technology Data Exchange (ETDEWEB)

Varykhalov, Andrei; Sanchez-Barriga, Jaime; Gudat, Wolfgang; Eberhardt, Wolfgang; Rader, Oliver [BESSY Berlin (Germany); Shikin, Alexander M. [St. Petersburg State University (Russian Federation)

2008-07-01

Elements with high atomic number Z lead to a large spin-orbit coupling. Such materials can be used to create spin-polarized electronic states without the presence of a ferromagnet or an external magnetic field if the solid exhibits an inversion asymmetry. We create large spin-orbit splittings using a tungsten crystal as substrate and break the structural inversion symmetry through deposition of a gold quantum film. Using spin- and angle-resolved photoelectron spectroscopy, it is demonstrated that quantum-well states forming in the gold film are spin-orbit split and spin polarized up to a thickness of at least 10 atomic layers. This is a considerable progress as compared to the current literature which reports spin-orbit split states at metal surfaces which are either pure or covered by at most a monoatomic layer of adsorbates.

Emergent spin electromagnetism induced by magnetization textures in the presence of spin-orbit interaction (invited)

Energy Technology Data Exchange (ETDEWEB)

Tatara, Gen, E-mail: gen.tatara@riken.jp [RIKEN Center for Emergent Matter Science (CEMS), 2-1 Hirosawa, Wako, Saitama 351-0198 Japan (Japan); Nakabayashi, Noriyuki [RIKEN Center for Emergent Matter Science (CEMS), 2-1 Hirosawa, Wako, Saitama 351-0198 Japan (Japan); Graduate School of Science and Engineering, Tokyo Metropolitan University, Hachioji, Tokyo 192-0397 Japan (Japan)

2014-05-07

Emergent electromagnetic field which couples to electron's spin in ferromagnetic metals is theoretically studied. Rashba spin-orbit interaction induces spin electromagnetic field which is in the linear order in gradient of magnetization texture. The Rashba-induced effective electric and magnetic fields satisfy in the absence of spin relaxation the Maxwell's equations as in the charge-based electromagnetism. When spin relaxation is taken into account besides spin dynamics, a monopole current emerges generating spin motive force via the Faraday's induction law. The monopole is expected to play an important role in spin-charge conversion and in the integration of spintronics into electronics.

Circuit-quantum electrodynamics with direct magnetic coupling to single-atom spin qubits in isotopically enriched 28Si

Directory of Open Access Journals (Sweden)

Guilherme Tosi

2014-08-01

Full Text Available Recent advances in silicon nanofabrication have allowed the manipulation of spin qubits that are extremely isolated from noise sources, being therefore the semiconductor equivalent of single atoms in vacuum. We investigate the possibility of directly coupling an electron spin qubit to a superconducting resonator magnetic vacuum field. By using resonators modified to increase the vacuum magnetic field at the qubit location, and isotopically purified 28Si substrates, it is possible to achieve coupling rates faster than the single spin dephasing. This opens up new avenues for circuit-quantum electrodynamics with spins, and provides a pathway for dispersive read-out of spin qubits via superconducting resonators.

Hybrid Circuit Quantum Electrodynamics: Coupling a Single Silicon Spin Qubit to a Photon

Science.gov (United States)

2015-01-01

776 (2008). 14. M. Pioro-Ladriere, Y. Tokura, T. Obata, T. Kubo , S. Tarucha, Micromagnets for coherent control of spin-charge qubit in lateral...slanting Zeeman field. Phys. Rev. Lett. 96, 047202 (2006). 16. Y. Kubo et al., Strong coupling of a spin ensemble to a superconducting resonator. Phys

Spin Waves in Terbium

DEFF Research Database (Denmark)

Jensen, J.; Houmann, Jens Christian Gylden

1975-01-01

The selection rules for the linear couplings between magnons and phonons propagating in the c direction of a simple basal-plane hcp ferromagnet are determined by general symmetry considerations. The acoustic-optical magnon-phonon interactions observed in the heavy-rare-earth metals have been...... explained by Liu as originating from the mixing of the spin states of the conduction electrons due to the spin-orbit coupling. We find that this coupling mechanism introduces interactions which violate the selection rules for a simple ferromagnet. The interactions between the magnons and phonons propagating...... in the c direction of Tb have been studied experimentally by means of inelastic neutron scattering. The magnons are coupled to both the acoustic- and optical-transverse phonons. By studying the behavior of the acoustic-optical coupling, we conclude that it is a spin-mixed-induced coupling as proposed...

Acoustic phonons mediated non-equilibrium spin current in the presence of Rashba and Dresselhaus spin–orbit couplings

International Nuclear Information System (INIS)

Hasanirokh, K.; Phirouznia, A.

2013-01-01

Influence of electrons interaction with longitudinal acoustic phonons on magnetoelectric and spin-related transport effects are investigated. The considered system is a two-dimensional electron gas system with both Rashba and Dresselhaus spin–orbit couplings. The works which have previously been performed in this field, have revealed that the Rashba and Dresselhaus couplings cannot be responsible for spin current in the non-equilibrium regime. In the current Letter, a semiclassical method was employed using the Boltzmann approach and it was shown that the spin current of the system, in general, does not go all the way to zero when the electron–phonon coupling is taken into account. It was also shown that spin accumulation of the system could be influenced by electron–phonon coupling.

Shot noise of spin current and spin transfer torque

International Nuclear Information System (INIS)

Yu Yunjin; Zhan Hongxin; Wan Langhui; Wang Bin; Wei Yadong; Sun Qingfeng; Wang Jian

2013-01-01

We report the theoretical investigation of the shot noise of the spin current (S σ ) and the spin transfer torque (S τ ) for non-collinear spin polarized transport in a spin-valve device which consists of a normal scattering region connected by two ferromagnetic electrodes (MNM system). Our theory was developed using the non-equilibrium Green’s function method, and general nonlinear S σ − V and S τ − V relations were derived as a function of the angle θ between the magnetizations of two leads. We have applied our theory to a quantum dot system with a resonant level coupled with two ferromagnetic electrodes. It was found that, for the MNM system, the auto-correlation of the spin current is enough to characterize the fluctuation of the spin current. For a system with three ferromagnetic layers, however, both auto-correlation and cross-correlation of the spin current are needed to characterize the noise of the spin current. For a quantum dot with a resonant level, the derivative of spin torque with respect to bias voltage is proportional to sinθ when the system is far away from resonance. When the system is near resonance, the spin transfer torque becomes a non-sinusoidal function of θ. The derivative of the noise of the spin transfer torque with respect to the bias voltage N τ behaves differently when the system is near or far away from resonance. Specifically, the differential shot noise of the spin transfer torque N τ is a concave function of θ near resonance while it becomes a convex function of θ far away from resonance. For certain bias voltages, the period N τ (θ) becomes π instead of 2π. For small θ, it was found that the differential shot noise of the spin transfer torque is very sensitive to the bias voltage and the other system parameters. (paper)

Exploiting level anti-crossings for efficient and selective transfer of hyperpolarization in coupled nuclear spin systems

NARCIS (Netherlands)

Pravdivtsev, A.N.; Yurkovskaya, A.V.; Kaptein, R.; Miesel, K.; Vieth, H.-M.; Ivanov, K.L.

2013-01-01

Spin hyperpolarization can be coherently transferred to other nuclei in field-cycling NMR experiments. At low magnetic fields spin polarization is redistributed in a strongly coupled network of spins. Polarization transfer is most efficient at fields where level anti-crossings (LACs) occur for the

Energy-level repulsion by spin-orbit coupling in two-dimensional Rydberg excitons

Science.gov (United States)

Stephanovich, V. A.; Sherman, E. Ya.; Zinner, N. T.; Marchukov, O. V.

2018-05-01

We study the effects of Rashba spin-orbit coupling on two-dimensional Rydberg exciton systems. Using analytical and numerical arguments we demonstrate that this coupling considerably modifies the wave functions and leads to a level repulsion that results in a deviation from the Poissonian statistics of the adjacent level distance distribution. This signifies the crossover to nonintegrability of the system and hints at the possibility of quantum chaos emerging. Such behavior strongly differs from the classical realization, where spin-orbit coupling produces highly entangled, chaotic electron trajectories in an exciton. We also calculate the oscillator strengths and show that randomization appears in the transitions between states with different total momenta.

Spin helical states and spin transport of the line defect in silicene lattice

Energy Technology Data Exchange (ETDEWEB)

Yang, Mou; Chen, Dong-Hai; Wang, Rui-Qiang [Laboratory of Quantum Engineering and Quantum Materials, School of Physics and Telecommunication Engineering, South China Normal University, Guangzhou 510006 (China); Bai, Yan-Kui, E-mail: ykbai@semi.ac.cn [College of Physical Science and Information Engineering and Hebei Advance Thin Films Laboratory, Hebei Normal University, Shijiazhuang, Hebei 050024 (China)

2015-02-06

We investigated the electronic structure of a silicene-like lattice with a line defect under the consideration of spin–orbit coupling. In the bulk energy gap, there are defect related bands corresponding to spin helical states localized beside the defect line: spin-up electrons flow forward on one side near the line defect and move backward on the other side, and vice versa for spin-down electrons. When the system is subjected to random distribution of spin-flipping scatterers, electrons suffer much less spin-flipped scattering when they transport along the line defect than in the bulk. An electric gate above the line defect can tune the spin-flipped transmission, which makes the line defect as a spin-controllable waveguide. - Highlights: • Band structure of silicene with a line defect. • Spin helical states around the line defect and their probability distribution features. • Spin transport along the line defect and that in the bulk silicene.

Circular-Polarization-Selective Transmission Induced by Spin-Orbit Coupling in a Helical Tape Waveguide

Science.gov (United States)

Liu, Yahong; Guo, Qinghua; Liu, Hongchao; Liu, Congcong; Song, Kun; Yang, Biao; Hou, Quanwen; Zhao, Xiaopeng; Zhang, Shuang; Navarro-Cía, Miguel

2018-05-01

Spin-orbit coupling of light, describing the interaction between the polarization (spin) and spatial degrees of freedom (orbit) of light, plays an important role in subwavelength scale systems and leads to many interesting phenomena, such as the spin Hall effect of light. Here, based on the spin-orbit coupling, we design and fabricate a helical tape waveguide (HTW), which can realize a circular-polarization-selective process. When the incident circularly polarized wave is of the same handedness as the helix of the HTW, a nearly complete transmission is observed; in contrast, a counterrotating circular polarization of incident wave results in a much lower transmission or is even totally blocked by the HTW. Indeed, both simulations and experiments reveal that the blocked component of power leaks through the helical aperture of the HTW and forms a conical beam analogous to helical Cherenkov radiation due to the conversion from the spin angular momentum to the orbital angular momentum. Our HTW structure demonstrates its potential as a polarization selector in a broadband frequency range.

Spin correlations and spin-wave excitations in Dirac-Weyl semimetals

Science.gov (United States)

Araki, Yasufumi; Nomura, Kentaro

We study correlations among magnetic dopants in three-dimensional Dirac and Weyl semimetals. Effective field theory for localized magnetic moments is derived by integrating out the itinerant electron degrees of freedom. We find that spin correlation in the spatial direction parallel to local magnetization is more rigid than that in the perpendicular direction, reflecting spin-momentum locking nature of the Dirac Hamiltonian. Such an anisotropy becomes stronger for Fermi level close to the Dirac points, due to Van Vleck paramagnetism triggered by spin-orbit coupling. One can expect topologically nontrivial spin textures under this anisotropy, such as a hedgehog around a single point, or a radial vortex around an axis, as well as a uniform ferromagnetic order. We further investigate the characteristics of spin waves in the ferromagnetic state. Spin-wave dispersion also shows a spatial anisotropy, which is less dispersed in the direction transverse to the magnetization than that in the longitudinal direction. The spin-wave dispersion anisotropy can be traced back to the rigidity and flexibility of spin correlations discussed above. This work was supported by Grant-in-Aid for Scientific Research (Grants No.15H05854, No.26107505, and No.26400308) from the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan.

Ultracoherent operation of spin qubits with superexchange coupling

Science.gov (United States)

Rančić, Marko J.; Burkard, Guido

2017-11-01

With the use of nuclear-spin-free materials such as silicon and germanium, spin-based quantum bits (qubits) have evolved to become among the most coherent systems for quantum information processing. The new frontier for spin qubits has therefore shifted to the ubiquitous charge noise and spin-orbit interaction, which are limiting the coherence times and gate fidelities of solid-state qubits. In this paper we investigate superexchange, as a means of indirect exchange interaction between two single electron spin qubits, each embedded in a single semiconductor quantum dot (QD), mediated by an intermediate, empty QD. Our results suggest the existence of "supersweet spots", in which the qubit operations implemented by superexchange interaction are simultaneously first-order-insensitive to charge noise and to errors due to spin-orbit interaction. The proposed spin-qubit architecture is scalable and within the manufacturing capabilities of semiconductor industry.

Spin-orbit coupling in ultracold Fermi gases of 173Yb atoms

Science.gov (United States)

Song, Bo; He, Chengdong; Hajiyev, Elnur; Ren, Zejian; Seo, Bojeong; Cai, Geyue; Amanov, Dovran; Zhang, Shanchao; Jo, Gyu-Boong

2017-04-01

Synthetic spin-orbit coupling (SOC) in cold atoms opens an intriguing new way to probe nontrivial topological orders beyond natural conditions. Here, we report the realization of the SOC physics both in a bulk system and in an optical lattice. First, we demonstrate two hallmarks induced from SOC in a bulk system, spin dephasing in the Rabi oscillation and asymmetric atomic distribution in the momentum space respectively. Then we describe the observation of non-trivial spin textures and the determination of the topological phase transition in a spin-dependent optical lattice dressed by the periodic Raman field. Furthermore, we discuss the quench dynamics between topological and trivial states by suddenly changing the band topology. Our work paves a new way to study non-equilibrium topological states in a controlled manner. Funded by Croucher Foundation and Research Grants Council (RGC) of Hong Kong (Project ECS26300014, GRF16300215, GRF16311516, and Croucher Innovation Grants).

Dynamic Spin-Lattice Coupling and Nematic Fluctuations in NaFeAs

Directory of Open Access Journals (Sweden)

Yu Li

2018-06-01

Full Text Available We use inelastic neutron scattering to study acoustic phonons and spin excitations in single crystals of NaFeAs, a parent compound of iron-pnictide superconductors. NaFeAs exhibits a tetragonal-to-orthorhombic structural transition at T_{s}≈58  K and a collinear antiferromagnetic order at T_{N}≈45  K. While longitudinal and out-of-plane transverse acoustic phonons behave as expected, the in-plane transverse acoustic phonons reveal considerable softening on cooling to T_{s} and then harden on approaching T_{N} before saturating below T_{N}. In addition, we find that spin-spin correlation lengths of low-energy magnetic excitations within the FeAs layer and along the c axis increase dramatically below T_{s} and show a weak anomaly across T_{N}. These results suggest that the electronic nematic phase present in the paramagnetic tetragonal phase is closely associated with dynamic spin-lattice coupling, possibly arising from the one-phonon–two-magnon mechanism.

New spin source to search for scalar-pseudoscalar couplings at short range

International Nuclear Information System (INIS)

Hammond, G. D.; Pulido Paton, A.; Speake, C. C.; Trenkel, C.; Rochester, G. K.; Shaul, D.; Sumner, T. J.

2008-01-01

We describe the design and performance of a new source of polarized spins that can be employed in experiments that search for macroscopic interactions between particles with intrinsic spin. In this article we concentrate on the analysis of the performance of the spin source in generating putative scalar-pseudoscalar forces. We outline two methods of calculating the magnitude of such forces and compare the predictions of the models. We discuss the manufacture of the spin source and the measurements that we have carried out in order to place upper limits on systematic effects that would limit the sensitivity of such searches. We have shown, in a recent article to Physical Review Letters [G. D. Hammond, C. C. Speake, C. Trenkel, and A. Pulido-Paton, Phys. Rev. Lett. 98, 081101 (2007)], that the combination of the spin source together with the torque sensitivity of our torsion balance improves constraints on the coupling strength of macroscopic scalar-pseudoscalar interactions by 10 orders of magnitude at a range of 1 mm. This paper further supports that work and provides a detailed description and characterization of the spin source

Entangled spins and ghost-spins

Directory of Open Access Journals (Sweden)

Dileep P. Jatkar

2017-09-01

Full Text Available We study patterns of quantum entanglement in systems of spins and ghost-spins regarding them as simple quantum mechanical toy models for theories containing negative norm states. We define a single ghost-spin as in [20] as a 2-state spin variable with an indefinite inner product in the state space. We find that whenever the spin sector is disentangled from the ghost-spin sector (both of which could be entangled within themselves, the reduced density matrix obtained by tracing over all the ghost-spins gives rise to positive entanglement entropy for positive norm states, while negative norm states have an entanglement entropy with a negative real part and a constant imaginary part. However when the spins are entangled with the ghost-spins, there are new entanglement patterns in general. For systems where the number of ghost-spins is even, it is possible to find subsectors of the Hilbert space where positive norm states always lead to positive entanglement entropy after tracing over the ghost-spins. With an odd number of ghost-spins however, we find that there always exist positive norm states with negative real part for entanglement entropy after tracing over the ghost-spins.

Repulsively interacting fermions in a two-dimensional deformed trap with spin-orbit coupling

DEFF Research Database (Denmark)

Marchukov, O. V.; Fedorov, D. V.; Jensen, A. S.

2015-01-01

We investigate a two-dimensional system of fermions with two internal (spin) degrees of freedom. It is confined by a deformed harmonic trap and subject to a Zeeman field, Rashba or Dresselhaus one-body spin-orbit couplings and two-body short range repulsion. We obtain self-consistent mean-field $N...

Gate control of the spin mobility through the modification of the spin-orbit interaction in two-dimensional systems

Science.gov (United States)

Luengo-Kovac, M.; Moraes, F. C. D.; Ferreira, G. J.; Ribeiro, A. S. L.; Gusev, G. M.; Bakarov, A. K.; Sih, V.; Hernandez, F. G. G.

2017-06-01

Spin drag measurements were performed in a two-dimensional electron system set close to the crossed spin helix regime and coupled by strong intersubband scattering. In a sample with an uncommon combination of long spin lifetime and high charge mobility, the drift transport allows us to determine the spin-orbit field and the spin mobility anisotropies. We used a random walk model to describe the system dynamics and found excellent agreement for the Rashba and Dresselhaus couplings. The proposed two-subband system displays a large tuning lever arm for the Rashba constant with gate voltage, which provides a new path towards a spin transistor. Furthermore, the data show large spin mobility controlled by the spin-orbit constants setting the field along the direction perpendicular to the drift velocity. This work directly reveals the resistance experienced in the transport of a spin-polarized packet as a function of the strength of anisotropic spin-orbit fields.

Floquet-Magnus expansion for general N-coupled spins systems in magic-angle spinning nuclear magnetic resonance spectra

Science.gov (United States)

Mananga, Eugene Stephane; Charpentier, Thibault

2015-04-01

In this paper we present a theoretical perturbative approach for describing the NMR spectrum of strongly dipolar-coupled spin systems under fast magic-angle spinning. Our treatment is based on two approaches: the Floquet approach and the Floquet-Magnus expansion. The Floquet approach is well known in the NMR community as a perturbative approach to get analytical approximations. Numerical procedures are based on step-by-step numerical integration of the corresponding differential equations. The Floquet-Magnus expansion is a perturbative approach of the Floquet theory. Furthermore, we address the " γ -encoding" effect using the Floquet-Magnus expansion approach. We show that the average over " γ " angle can be performed for any Hamiltonian with γ symmetry.

Prominent Role of Spin-Orbit Coupling in FeSe Revealed by Inelastic Neutron Scattering

Directory of Open Access Journals (Sweden)

Mingwei Ma

2017-05-01

Full Text Available In most existing theories for iron-based superconductors, spin-orbit coupling (SOC has been assumed to be insignificant. Here, we use spin-polarized inelastic neutron scattering to show that collective low-energy spin excitations in the orthorhombic (or “nematic” phase of FeSe possess nearly no in-plane component. Such spin-space anisotropy is present over an energy range greater than the superconducting gap 2Δ_{sc} and gets fully inherited in the superconducting state, resulting in a c-axis polarized “spin resonance” without any noticeable isotropic spectral-weight rearrangement related to the superconductivity, which is distinct from observations in the superconducting iron pnictides. The contrast between the strong suppression of long-range magnetic order in FeSe and the persisting large spin-space anisotropy, which cannot be explained microscopically by introducing single-ion anisotropy into local-moment spin models, demonstrates the importance of SOC in an itinerant-electron description of the low-energy spin excitations. Our result helps to elucidate the nearby magnetic instabilities and the debated interplay between spin and orbital degrees of freedom in FeSe. The prominent role of SOC also implies a possible unusual nature of the superconducting state.

Collective spin correlations and entangled state dynamics in coupled quantum dots

Science.gov (United States)

Maslova, N. S.; Arseyev, P. I.; Mantsevich, V. N.

2018-02-01

Here we demonstrate that the dynamics of few-electron states in a correlated quantum-dot system coupled to an electronic reservoir is governed by the symmetry properties of the total system leading to the collective behavior of all the electrons. Time evolution of two-electron states in a correlated double quantum dot after coupling to the reservoir has been analyzed by means of kinetic equations for pseudoparticle occupation numbers with constraint on possible physical states. It was revealed that the absolute value of the spin correlation function and the degree of entanglement for two-electron states could considerably increase after coupling to the reservoir. The obtained results demonstrate the possibility of a controllable tuning of both the spin correlation function and the concurrence value in a coupled quantum-dot system by changing of the gate voltage applied to the barrier separating the dots.

Spin Hall effects

Science.gov (United States)

Sinova, Jairo; Valenzuela, Sergio O.; Wunderlich, J.; Back, C. H.; Jungwirth, T.

2015-10-01

Spin Hall effects are a collection of relativistic spin-orbit coupling phenomena in which electrical currents can generate transverse spin currents and vice versa. Despite being observed only a decade ago, these effects are already ubiquitous within spintronics, as standard spin-current generators and detectors. Here the theoretical and experimental results that have established this subfield of spintronics are reviewed. The focus is on the results that have converged to give us the current understanding of the phenomena, which has evolved from a qualitative to a more quantitative measurement of spin currents and their associated spin accumulation. Within the experimental framework, optical-, transport-, and magnetization-dynamics-based measurements are reviewed and linked to both phenomenological and microscopic theories of the effect. Within the theoretical framework, the basic mechanisms in both the extrinsic and intrinsic regimes are reviewed, which are linked to the mechanisms present in their closely related phenomenon in ferromagnets, the anomalous Hall effect. Also reviewed is the connection to the phenomenological treatment based on spin-diffusion equations applicable to certain regimes, as well as the spin-pumping theory of spin generation used in many measurements of the spin Hall angle. A further connection to the spin-current-generating spin Hall effect to the inverse spin galvanic effect is given, in which an electrical current induces a nonequilibrium spin polarization. This effect often accompanies the spin Hall effect since they share common microscopic origins. Both can exhibit the same symmetries when present in structures comprising ferromagnetic and nonmagnetic layers through their induced current-driven spin torques or induced voltages. Although a short chronological overview of the evolution of the spin Hall effect field and the resolution of some early controversies is given, the main body of this review is structured from a pedagogical

Signatures of a quantum dynamical phase transition in a three-spin system in presence of a spin environment

International Nuclear Information System (INIS)

Alvarez, Gonzalo A.; Levstein, Patricia R.; Pastawski, Horacio M.

2007-01-01

We have observed an environmentally induced quantum dynamical phase transition in the dynamics of a two-spin experimental swapping gate [G.A. Alvarez, E.P. Danieli, P.R. Levstein, H.M. Pastawski, J. Chem. Phys. 124 (2006) 194507]. There, the exchange of the coupled states vertical bar ↑,↓> and vertical bar ↓,↑> gives an oscillation with a Rabi frequency b/ℎ (the spin-spin coupling). The interaction, ℎ/τ SE with a spin-bath degrades the oscillation with a characteristic decoherence time. We showed that the swapping regime is restricted only to bτ SE > or approx. ℎ. However, beyond a critical interaction with the environment the swapping freezes and the system enters to a Quantum Zeno dynamical phase where relaxation decreases as coupling with the environment increases. Here, we solve the quantum dynamics of a two-spin system coupled to a spin-bath within a Liouville-von Neumann quantum master equation and we compare the results with our previous work within the Keldysh formalism. Then, we extend the model to a three interacting spin system where only one is coupled to the environment. Beyond a critical interaction the two spins not coupled to the environment oscillate with the bare Rabi frequency and relax more slowly. This effect is more pronounced when the anisotropy of the system-environment (SE) interaction goes from a purely XY to an Ising interaction form

Classical electromagnetic non-minimal coupling for spin 3/2 fields

International Nuclear Information System (INIS)

Villanueva, V. M.; Obregon, O.; Nieto, J. A.

1996-01-01

We obtain a non-minimal electromagnetic coupling for spin 3/2 particles from linearized N=2 Supergravity. This coupling coincides with the one found by Ferrara et al. by demanding g=2 at the tree level. Linearized Einstein field equations plus interaction terms are obtained by squaring the Rarita-Schwinger with this non-minimal coupling by using generalized Poisson brackets

Full four-component relativistic calculations of the one-bond 77Se-13C spin-spin coupling constants in the series of selenium heterocycles and their parent open-chain selenides.

Science.gov (United States)

Rusakov, Yury Yu; Rusakova, Irina L; Krivdin, Leonid B

2014-05-01

Four-component relativistic calculations of (77)Se-(13)C spin-spin coupling constants have been performed in the series of selenium heterocycles and their parent open-chain selenides. It has been found that relativistic effects play an essential role in the selenium-carbon coupling mechanism and could result in a contribution of as much as 15-25% of the total values of the one-bond selenium-carbon spin-spin coupling constants. In the overall contribution of the relativistic effects to the total values of (1)J(Se,C), the scalar relativistic corrections (negative in sign) by far dominate over the spin-orbit ones (positive in sign), the latter being of less than 5%, as compared to the former (ca 20%). A combination of nonrelativistic second-order polarization propagator approach (CC2) with the four-component relativistic density functional theory scheme is recommended as a versatile tool for the calculation of (1)J(Se,C). Solvent effects in the values of (1)J(Se,C) calculated within the polarizable continuum model for the solvents with different dielectric constants (ε 2.2-78.4) are next to negligible decreasing negative (1)J(Se,C) in absolute value by only about 1 Hz. The use of the locally dense basis set approach applied herewith for the calculation of (77)Se-(13)C spin-spin coupling constants is fully justified resulting in a dramatic decrease in computational cost with only 0.1-0.2-Hz loss of accuracy. Copyright © 2014 John Wiley & Sons, Ltd.

Constrained dynamics of universally coupled massive spin 2-spin 0 gravities

International Nuclear Information System (INIS)

Pitts, J Brian

2006-01-01

The 2-parameter family of massive variants of Einsteins gravity (on a Minkowski background) found by Ogievetsky and Polubarinov by excluding lower spins can also be derived using universal coupling. A Dirac-Bergmann constrained dynamics analysis seems not to have been presented for these theories, the Freund-Maheshwari-Schonberg special case, or any other massive gravity beyond the linear level treated by Marzban, Whiting and van Dam. Here the Dirac-Bergmann apparatus is applied to these theories. A few remarks are made on the question of positive energy. Being bimetric, massive gravities have a causality puzzle, but it appears soluble by the introduction and judicious use of gauge freedom

Spin waves in the soft layer of exchange-coupled soft/hard bilayers

Energy Technology Data Exchange (ETDEWEB)

Xiong, Zheng-min; Ge, Su-qin; Wang, Xi-guang; Li, Zhi-xiong; Xia, Qing-lin; Wang, Dao-wei; Nie, Yao-zhuang; Guo, Guang-hua, E-mail: guogh@mail.csu.edu.cn [School of Physics and Electronics, Central South University, Changsha 410083 (China); Tang, Wei [School of Physics and Electronics, Central South University, Changsha 410083 (China); Suzhou Institute of Nano-tech and Nano-bionics, Chinese Academy of Sciences, Suzhou 215123 (China); Zeng, Zhong-ming [Suzhou Institute of Nano-tech and Nano-bionics, Chinese Academy of Sciences, Suzhou 215123 (China)

2016-05-15

The magnetic dynamical properties of the soft layer in exchange-coupled soft/hard bilayers have been investigated numerically using a one-dimensional atomic chain model. The frequencies and spatial profiles of spin wave eigenmodes are calculated during the magnetization reversal process of the soft layer. The spin wave modes exhibit a spatially modulated amplitude, which is especially evident for high-order modes. A dynamic pinning effect of surface magnetic moment is observed. The spin wave eigenfrequency decreases linearly with the increase of the magnetic field in the uniformly magnetized state and increases nonlinearly with field when spiral magnetization configuration is formed in the soft layer.

Spin waves in the soft layer of exchange-coupled soft/hard bilayers

Directory of Open Access Journals (Sweden)

Zheng-min Xiong

2016-05-01

Full Text Available The magnetic dynamical properties of the soft layer in exchange-coupled soft/hard bilayers have been investigated numerically using a one-dimensional atomic chain model. The frequencies and spatial profiles of spin wave eigenmodes are calculated during the magnetization reversal process of the soft layer. The spin wave modes exhibit a spatially modulated amplitude, which is especially evident for high-order modes. A dynamic pinning effect of surface magnetic moment is observed. The spin wave eigenfrequency decreases linearly with the increase of the magnetic field in the uniformly magnetized state and increases nonlinearly with field when spiral magnetization configuration is formed in the soft layer.

Magnetic proximity control of spin currents and giant spin accumulation in graphene

Science.gov (United States)

Singh, Simranjeet

Two dimensional (2D) materials provide a unique platform to explore the full potential of magnetic proximity driven phenomena. We will present the experimental study showing the strong modulation of spin currents in graphene layers by controlling the direction of the exchange field due to the ferromagnetic-insulator (FMI) magnetization in graphene/FMI heterostructures. Owing to clean interfaces, a strong magnetic exchange coupling leads to the experimental observation of complete spin modulation at low externally applied magnetic fields in short graphene channels. We also discover that the graphene spin current can be fully dephased by randomly fluctuating exchange fields. This is manifested as an unusually strong temperature dependence of the non-local spin signals in graphene, which is due to spin relaxation by thermally-induced transverse fluctuations of the FMI magnetization. Additionally, it has been a challenge to grow a smooth, robust and pin-hole free tunnel barriers on graphene, which can withstand large current densities for efficient electrical spin injection. We have experimentally demonstrated giant spin accumulation in graphene lateral spin valves employing SrO tunnel barriers. Nonlocal spin signals, as large as 2 mV, are observed in graphene lateral spin valves at room temperature. This high spin accumulations observed using SrO tunnel barriers puts graphene on the roadmap for exploring the possibility of achieving a non-local magnetization switching due to the spin torque from electrically injected spins. Financial support from ONR (No. N00014-14-1-0350), NSF (No. DMR-1310661), and C-SPIN, one of the six SRC STARnet Centers, sponsored by MARCO and DARPA.

Topological quantum phase transitions and edge states in spin-orbital coupled Fermi gases.

Science.gov (United States)

Zhou, Tao; Gao, Yi; Wang, Z D

2014-06-11

We study superconducting states in the presence of spin-orbital coupling and Zeeman field. It is found that a phase transition from a Fulde-Ferrell-Larkin-Ovchinnikov state to the topological superconducting state occurs upon increasing the spin-orbital coupling. The nature of this topological phase transition and its critical property are investigated numerically. Physical properties of the topological superconducting phase are also explored. Moreover, the local density of states is calculated, through which the topological feature may be tested experimentally.

Disentanglement of two qubits coupled to an XY spin chain: Role of quantum phase transition

International Nuclear Information System (INIS)

Yuan Zigang; Li Shushen; Zhang Ping

2007-01-01

We study the disentanglement evolution of two spin qubits which interact with a general XY spin-chain environment. The dynamical process of the disentanglement is numerically and analytically investigated in the vicinity of a quantum phase transition (QPT) of the spin chain in both weak and strong coupling cases. We find that the disentanglement of the two spin qubits may be greatly enhanced by the quantum critical behavior of the environmental spin chain. We give a detailed analysis to facilitate the understanding of the QPT-enhanced decaying behavior of the coherence factor. Furthermore, the scaling behavior in the disentanglement dynamics is also revealed and analyzed

Spin interferometry in anisotropic spin-orbit fields

Science.gov (United States)

Saarikoski, Henri; Reynoso, Andres A.; Baltanás, José Pablo; Frustaglia, Diego; Nitta, Junsaku

2018-03-01

Electron spins in a two-dimensional electron gas can be manipulated by spin-orbit (SO) fields originating from either Rashba or Dresselhaus interactions with independent isotropic characteristics. Together, though, they produce anisotropic SO fields with consequences on quantum transport through spin interference. Here we study the transport properties of modeled mesoscopic rings subject to Rashba and Dresselhaus [001] SO couplings in the presence of an additional in-plane Zeeman field acting as a probe. By means of one- and two-dimensional quantum transport simulations we show that this setting presents anisotropies in the quantum resistance as a function of the Zeeman field direction. Moreover, the anisotropic resistance can be tuned by the Rashba strength up to the point to invert its response to the Zeeman field. We also find that a topological transition in the field texture that is associated with a geometric phase switching is imprinted in the anisotropy pattern. We conclude that resistance anisotropy measurements can reveal signatures of SO textures and geometric phases in spin carriers.

Spin-orbit coupling induced two-electron relaxation in silicon donor pairs

Science.gov (United States)

Song, Yang; Das Sarma, S.

2017-09-01

We unravel theoretically a key intrinsic relaxation mechanism among the low-lying singlet and triplet donor-pair states in silicon, an important element in the fast-developing field of spintronics and quantum computation. Despite the perceived weak spin-orbit coupling (SOC) in Si, we find that our discovered relaxation mechanism, combined with the electron-phonon and interdonor interactions, drives the transitions in the two-electron states over a large range of donor coupling regimes. The scaling of the relaxation rate with interdonor exchange interaction J goes from J5 to J4 at the low to high temperature limits. Our analytical study draws on the symmetry analysis over combined band, donor envelope, and valley configurations. It uncovers naturally the dependence on the donor-alignment direction and triplet spin orientation, and especially on the dominant SOC source from donor impurities. While a magnetic field is not necessary for this relaxation, unlike in the single-donor spin relaxation, we discuss the crossover behavior with increasing Zeeman energy in order to facilitate comparison with experiments.

Geometrical spin symmetry and spin

International Nuclear Information System (INIS)

Pestov, I. B.

2011-01-01

Unification of General Theory of Relativity and Quantum Mechanics leads to General Quantum Mechanics which includes into itself spindynamics as a theory of spin phenomena. The key concepts of spindynamics are geometrical spin symmetry and the spin field (space of defining representation of spin symmetry). The essence of spin is the bipolar structure of geometrical spin symmetry induced by the gravitational potential. The bipolar structure provides a natural derivation of the equations of spindynamics. Spindynamics involves all phenomena connected with spin and provides new understanding of the strong interaction.

Strong spin-filtering and spin-valve effects in a molecular V-C-60-V contact

DEFF Research Database (Denmark)

Koleini, Mohammad; Brandbyge, Mads

2012-01-01

Motivated by the recent achievements in the manipulation of C-60 molecules in STM experiments, we study theoretically the structure and electronic properties of a C-60 molecule in an STM tunneljunction with a magnetic tip and magnetic adatom on a Cu(111) surface using first-principles calculations....... For the case of a vanadium tip/adatom, we demonstrate how spin coupling between the magnetic V atoms, mediated by the C-60, can be observed in the electronic transport, which display a strong spin-filtering effect, allowing mainly majority-spin electrons to pass (>95%). Moreover, we find a significant change...... in the conductance between parallel and anti-parallel spin polarizations in the junction (86%) which suggests that STM experiments should be able to characterize the magnetism and spin coupling for these systems....

Towards quantifying the role of exact exchange in the prediction hydrogen bond spin-spin coupling constants involving fluorine

Energy Technology Data Exchange (ETDEWEB)

San Fabián, J.; Omar, S.; García de la Vega, J. M., E-mail: garcia.delavega@uam.es [Departamento de Química Física Aplicada, Facultad de Ciencias, Universidad Autónoma de Madrid, Madrid (Spain)

2016-08-28

The effect of a fraction of Hartree-Fock exchange on the calculated spin-spin coupling constants involving fluorine through a hydrogen bond is analyzed in detail. Coupling constants calculated using wavefunction methods are revisited in order to get high-level calculations using the same basis set. Accurate MCSCF results are obtained using an additive approach. These constants and their contributions are used as a reference for density functional calculations. Within the density functional theory, the Hartree-Fock exchange functional is split in short- and long-range using a modified version of the Coulomb-attenuating method with the SLYP functional as well as with the original B3LYP. Results support the difficulties for calculating hydrogen bond coupling constants using density functional methods when fluorine nuclei are involved. Coupling constants are very sensitive to the Hartree-Fock exchange and it seems that, contrary to other properties, it is important to include this exchange for short-range interactions. Best functionals are tested in two different groups of complexes: those related with anionic clusters of type [F(HF){sub n}]{sup −} and those formed by difluoroacetylene and either one or two hydrogen fluoride molecules.

The spin-Peierls chain revisited

International Nuclear Information System (INIS)

Hager, Georg; Weisse, Alexander; Wellein, Gerhard; Jeckelmann, Eric; Fehske, Holger

2007-01-01

We extend previous analytical studies of the ground-state phase diagram of a one-dimensional Heisenberg spin chain coupled to optical phonons, which for increasing spin-lattice coupling undergoes a quantum phase transition from a gapless to a gaped phase with finite lattice dimerisation. We check the analytical results against established four-block and new two-block density matrix renormalisation group (DMRG) calculations. Different finite-size scaling behaviour of the spin excitation gaps is found in the adiabatic and anti-adiabatic regimes

Spin Torques in Systems with Spin Filtering and Spin Orbit Interaction

KAUST Repository

Ortiz Pauyac, Christian

2016-06-19

In the present thesis we introduce the reader to the field of spintronics and explore new phenomena, such as spin transfer torques, spin filtering, and three types of spin-orbit torques, Rashba, spin Hall, and spin swapping, which have emerged very recently and are promising candidates for a new generation of memory devices in computer technology. A general overview of these phenomena is presented in Chap. 1. In Chap. 2 we study spin transfer torques in tunnel junctions in the presence of spin filtering. In Chap. 3 we discuss the Rashba torque in ferromagnetic films, and in Chap. 4 we study spin Hall effect and spin swapping in ferromagnetic films, exploring the nature of spin-orbit torques based on these mechanisms. Conclusions and perspectives are summarized in Chap. 5.

Statistical properties of spectra in harmonically trapped spin-orbit coupled systems

DEFF Research Database (Denmark)

V. Marchukov, O.; G. Volosniev, A.; V. Fedorov, D.

2014-01-01

We compute single-particle energy spectra for a one-body Hamiltonian consisting of a two-dimensional deformed harmonic oscillator potential, the Rashba spin-orbit coupling and the Zeeman term. To investigate the statistical properties of the obtained spectra as functions of deformation, spin......-orbit and Zeeman strengths we examine the distributions of the nearest neighbor spacings. We find that the shapes of these distributions depend strongly on the three potential parameters. We show that the obtained shapes in some cases can be well approximated with the standard Poisson, Brody and Wigner...... distributions. The Brody and Wigner distributions characterize irregular motion and help identify quantum chaotic systems. We present a special choices of deformation and spin-orbit strengths without the Zeeman term which provide a fair reproduction of the fourth-power repelling Wigner distribution. By adding...

Effect of cubic Dresselhaus interaction on the longitudinal optical conductivity of a spin-orbit coupled system

Science.gov (United States)

Cruz, Elmer; López-Bastidas, Catalina; Maytorena, Jesús A.

2018-03-01

We investigate the effect of the oft-neglected cubic terms of the Dresselhaus spin-orbit coupling on the longitudinal current response of a two-dimensional electron gas with both Rashba and linear Dresselhaus interactions. For a quantum well grown in the [001] direction, the changes caused by these nonlinear-in-momentum terms on the absorption spectrum become more notable under SU(2) symmetry conditions, when the Rashba and linear Dresselhaus coupling strengths are tuned to be equal. The longitudinal optical response no longer vanishes then and shows a strong dependence on the direction of the externally applied electric field, giving a signature of the relative size of several spin-orbit contributions. This anisotropic response arises from the nonisotropic splitting of the spin states induced by the interplay of Rashba and Dresselhaus couplings. However, the presence of cubic terms introduces characteristic spectral features and can modify the overall shape of the spectra for some values of the relative sizes of the spin-orbit parameters. We compare this behavior to the case of a sample with [110] crystal orientation which, under conditions of spin-preserving symmetry, has a collinear spin-orbit vector field that leads to vanishing conductivity, even in the presence of cubic terms. In addition to the control through the driven frequency or electrical gating, such a directional aspect of the current response suggests new ways of manipulation and supports the use of interband optics as a sensitive probe of spin-orbit mechanisms in semiconductor spintronics.

Current-induced Rashba spin orbit torque in silicene

Energy Technology Data Exchange (ETDEWEB)

Chen, Ji, E-mail: muze7777@hdu.edu.cn [Department of Mathematics, School of Science, Hangzhou Dianzi University, Hangzhou 310018 (China); Peng, Yingzi [Department of Physics, School of Science, Hangzhou Dianzi University, Hangzhou 310018 (China); Center for Integrated Spintronic Devices, Hangzhou Dianzi University, Hangzhou 310018 (China); Zhou, Jie [Department of Mathematics, School of Science, Hangzhou Dianzi University, Hangzhou 310018 (China)

2017-06-15

Highlights: • The spin dynamics of a ferromagnetic layer coupled to a silicene is investigated. • The Rashba spin orbit torque is obtained and the well-known LLG equation is modified. • The explicit forms of spin orbit torques in Domain Wall and vortex is also obtained. - Abstract: We study theoretically the spin torque of a ferromagnetic layer coupled to a silicene in the presence of the intrinsic Rashba spin orbit coupling (RSOC) effect. By using gauge field method, we find that under the applied current, the RSOC can induce an effective field which will result in the spin precession of conduction electron without applying any magnetic field. We also derive the spin torques due to the RSOC, which generalize the Landau-Lifshitz-Gilbert (LLG) equation. The spin torques are related to the applied current, the carrier density and Rashba strength of the system.

Nonlinear stability of spin-flip excitations

International Nuclear Information System (INIS)

Arunasalam, V.

1975-01-01

A rather complete discussion of the nonlinear electrodynamic behavior of a negative-temperature spin system is presented. The method presented here is based on a coupled set of master equations, one describing the time evolution of the photon (i.e., the spin-flip excitation) distribution function and the other describing the time evolution of the particle distribution function. It is found that the initially unstable (i.e., growing) spin-flip excitations grow to such a large amplitude that their nonlinear reaction on the particle distribution function becomes important. It is then shown that the initially totally inverted two-level spin system evolves rapidly (through this nonlinear photon-particle coupling) towards a quasilinear steady state where the populations of the spin-up and the spin-down states are equal to each other. Explicit expressions for the time taken to reach this quasilinear steady state and the energy in the spin-flip excitations at this state are also presented

Persistent spin helices in 2D electron systems

Science.gov (United States)

Kozulin, A. S.; Malyshev, A. I.; Konakov, A. A.

2017-03-01

We present a theoretical investigation of persistent spin helices in two-dimensional electron systems with spin-orbit coupling. For this purpose, we consider a single-particle effective mass Hamiltonian with a generalized linear-in- k spin-orbit coupling term corresponding to a quantum well grown in an arbitrary crystallographic direction, and derive the general condition for the formation of the persistent spin helix. This condition applied for the Hamiltonians describing quantum wells with different growth directions indicates the possibility of existence of the persistent spin helix in a wide class of 2D systems apart from the [001] model with equal Rashba and Dresselhaus spin-orbit coupling strengths and the [110] Dresselhaus model.

Action Potential Modulation of Neural Spin Networks Suggests Possible Role of Spin

CERN Document Server

Hu, H P

2004-01-01

In this paper we show that nuclear spin networks in neural membranes are modulated by action potentials through J-coupling, dipolar coupling and chemical shielding tensors and perturbed by microscopically strong and fluctuating internal magnetic fields produced largely by paramagnetic oxygen. We suggest that these spin networks could be involved in brain functions since said modulation inputs information carried by the neural spike trains into them, said perturbation activates various dynamics within them and the combination of the two likely produce stochastic resonance thus synchronizing said dynamics to the neural firings. Although quantum coherence is desirable and may indeed exist, it is not required for these spin networks to serve as the subatomic components for the conventional neural networks.

Impact of Disorder on Spin Dependent Transport Phenomena

KAUST Repository

Saidaoui, Hamed

2016-07-03

The impact of the spin degree of freedom on the transport properties of electrons traveling through magnetic materials has been known since the pioneer work of Mott [1]. Since then it has been demonstrated that the spin angular momentum plays a key role in the scattering process of electrons in magnetic multilayers. This role has been emphasized by the discovery of the Giant Magnetoresistance in 1988 by Fert and Grunberg [2, 3]. Among the numerous applications and effects that emerged in mesoscopic devices two mechanisms have attracted our attention during the course of this thesis: the spin transfer torque and the spin Hall effects. The former consists in the transfer of the spin angular momentum from itinerant carriers to local magnetic moments [4]. This mechanism results in the current-driven magnetization switching and excitations, which has potential application in terms of magnetic data storage and non-volatile memories. The latter, spin Hall effect, is considered as well to be one of the most fascinating mechanisms in condensed matter physics due to its ability of generating non-equilibrium spin currents without the need for any magnetic materials. In fact the spin Hall effect relies only on the presence of the spin-orbit interaction in order to create an imbalance between the majority and minority spins. The objective of this thesis is to investigate the impact of disorder on spin dependent transport phenomena. To do so, we identified three classes of systems on which such disorder may have a dramatic influence: (i) antiferromagnetic materials, (ii) impurity-driven spin-orbit coupled systems and (iii) two dimensional semiconducting electron gases with Rashba spin-orbit coupling. Antiferromagnetic materials - We showed that in antiferromagnetic spin-valves, spin transfer torque is highly sensitive to disorder, which prevents its experimental observation. To solve this issue, we proposed to use either a tunnel barrier as a spacer or a local spin torque using

Quantum group spin nets: Refinement limit and relation to spin foams

Science.gov (United States)

Dittrich, Bianca; Martin-Benito, Mercedes; Steinhaus, Sebastian

2014-07-01

So far spin foam models are hardly understood beyond a few of their basic building blocks. To make progress on this question, we define analogue spin foam models, so-called "spin nets," for quantum groups SU(2)k and examine their effective continuum dynamics via tensor network renormalization. In the refinement limit of this coarse-graining procedure, we find a vast nontrivial fixed-point structure beyond the degenerate and the BF phase. In comparison to previous work, we use fixed-point intertwiners, inspired by Reisenberger's construction principle [M. P. Reisenberger, J. Math. Phys. (N.Y.) 40, 2046 (1999)] and the recent work [B. Dittrich and W. Kaminski, arXiv:1311.1798], as the initial parametrization. In this new parametrization fine-tuning is not required in order to flow to these new fixed points. Encouragingly, each fixed point has an associated extended phase, which allows for the study of phase transitions in the future. Finally we also present an interpretation of spin nets in terms of melonic spin foams. The coarse-graining flow of spin nets can thus be interpreted as describing the effective coupling between two spin foam vertices or space time atoms.

Spin tunneling and manipulation in nanostructures.

Science.gov (United States)

Sherman, E Ya; Ban, Yue; Gulyaev, L V; Khomitsky, D V

2012-09-01

The results for joint effects of tunneling and spin-orbit coupling on spin dynamics in nanostructures are presented for systems with discrete and continuous spectra. We demonstrate that tunneling plays the crucial role in the spin dynamics and the abilities of spin manipulation by external electric field. This result can be important for design of nanostructures-based spintronics devices.

Spin-dependent electron-phonon coupling in the valence band of single-layer WS₂

DEFF Research Database (Denmark)

Hinsche, Nicki Frank; Ngankeu, Arlette S.; Guilloy, Kevin

2017-01-01

The absence of inversion symmetry leads to a strong spin-orbit splitting of the upper valence band of semiconducting single-layer transition-metal dichalchogenides such as MoS2 or WS2. This permits a direct comparison of the electron-phonon coupling strength in states that only differ by their spin....... Here, the electron-phonon coupling in the valence band maximum of single-layer WS2 is studied by first-principles calculations and angle-resolved photoemission. The coupling strength is found to be drastically different for the two spin-split branches, with calculated values of λK=0.0021 and 0.......40 for the upper and lower spin-split valence band of the freestanding layer, respectively. This difference is somewhat reduced when including scattering processes involving the Au(111) substrate present in the experiment but it remains significant, in good agreement with the experimental results....

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

Spin-polarized spin excitation spectroscopy

International Nuclear Information System (INIS)

Loth, Sebastian; Lutz, Christopher P; Heinrich, Andreas J

2010-01-01

We report on the spin dependence of elastic and inelastic electron tunneling through transition metal atoms. Mn, Fe and Cu atoms were deposited onto a monolayer of Cu 2 N on Cu(100) and individually addressed with the probe tip of a scanning tunneling microscope. Electrons tunneling between the tip and the substrate exchange energy and spin angular momentum with the surface-bound magnetic atoms. The conservation of energy during the tunneling process results in a distinct onset threshold voltage above which the tunneling electrons create spin excitations in the Mn and Fe atoms. Here we show that the additional conservation of spin angular momentum leads to different cross-sections for spin excitations depending on the relative alignment of the surface spin and the spin of the tunneling electron. For this purpose, we developed a technique for measuring the same local spin with a spin-polarized and a non-spin-polarized tip by exchanging the last apex atom of the probe tip between different transition metal atoms. We derive a quantitative model describing the observed excitation cross-sections on the basis of an exchange scattering process.

Strong spin-filtering and spin-valve effects in a molecular V–C60–V contact

Directory of Open Access Journals (Sweden)

Mohammad Koleini

2012-08-01

Full Text Available Motivated by the recent achievements in the manipulation of C60 molecules in STM experiments, we study theoretically the structure and electronic properties of a C60 molecule in an STM tunneljunction with a magnetic tip and magnetic adatom on a Cu(111 surface using first-principles calculations. For the case of a vanadium tip/adatom, we demonstrate how spin coupling between the magnetic V atoms, mediated by the C60, can be observed in the electronic transport, which display a strong spin-filtering effect, allowing mainly majority-spin electrons to pass (>95%. Moreover, we find a significant change in the conductance between parallel and anti-parallel spin polarizations in the junction (86% which suggests that STM experiments should be able to characterize the magnetism and spin coupling for these systems.

Spin Transport in Semiconductor heterostructures

International Nuclear Information System (INIS)

Marinescu, Domnita Catalina

2011-01-01

The focus of the research performed under this grant has been the investigation of spin transport in magnetic semiconductor heterostructures. The interest in these systems is motivated both by their intriguing physical properties, as the physical embodiment of a spin-polarized Fermi liquid, as well as by their potential applications as spintronics devices. In our work we have analyzed several different problems that affect the spin dynamics in single and bi-layer spin-polarized two-dimensional (2D) systems. The topics of interests ranged from the fundamental aspects of the electron-electron interactions, to collective spin and charge density excitations and spin transport in the presence of the spin-orbit coupling. The common denominator of these subjects is the impact at the macroscopic scale of the spin-dependent electron-electron interaction, which plays a much more subtle role than in unpolarized electron systems. Our calculations of several measurable parameters, such as the excitation frequencies of magneto-plasma modes, the spin mass, and the spin transresistivity, propose realistic theoretical estimates of the opposite-spin many-body effects, in particular opposite-spin correlations, that can be directly connected with experimental measurements.

Semiclassical spin transport in spin-orbit-coupled bands

Czech Academy of Sciences Publication Activity Database

Culcer, D.; Sinova, J.; Sinitsyn, N. A.; Jungwirth, Tomáš; MacDonald, A. H.; Niu, Q.

2004-01-01

Roč. 93, č. 4 (2004), 046602/1-046602/4 ISSN 0031-9007 R&D Projects: GA ČR GA202/02/0912 Institutional research plan: CEZ:AV0Z1010914 Keywords : spin Hall effect * semiconductor spintronics Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 7.218, year: 2004

Spin-orbit-coupling induced torque in ballistic domain walls: Equivalence of charge-pumping and nonequilibrium magnetization formalisms

NARCIS (Netherlands)

Yuan, Z.; Kelly, Paul J.

2016-01-01

To study the effect of spin-orbit coupling (SOC) on spin-transfer torque in magnetic materials, we have implemented two theoretical formalisms that can accommodate SOC. Using the “charge-pumping” formalism, we find two contributions to the out-of-plane spin-transfer torque parameter β in ballistic

Self-consistent treatment of spin and magnetization dynamic effect in spin transfer switching

International Nuclear Information System (INIS)

Guo Jie; Tan, Seng Ghee; Jalil, Mansoor Bin Abdul; Koh, Dax Enshan; Han, Guchang; Meng, Hao

2011-01-01

The effect of itinerant spin moment (m) dynamic in spin transfer switching has been ignored in most previous theoretical studies of the magnetization (M) dynamics. Thus in this paper, we proposed a more refined micromagnetic model of spin transfer switching that takes into account in a self-consistent manner of the coupled m and M dynamics. The numerical results obtained from this model further shed insight on the switching profiles of m and M, both of which show particular sensitivity to parameters such as the anisotropy field, the spin torque field, and the initial deviation between m and M.

Spin-orbit coupling effects, interactions and superconducting transport in nanostructures

Energy Technology Data Exchange (ETDEWEB)

Schulz, Andreas

2010-05-15

In the present thesis we study the electronic properties of several low dimensional nanoscale systems. In the first part, we focus on the combined effect of spin-orbit coupling (SOI) and Coulomb interaction in carbon nanotubes (CNTs) as well as quantum wires. We derive low energy theories for both systems, using the bosonization technique and obtain analytic expressions for the correlation functions that allow us to compute basically all observables of interest. We first focus on CNTs and show that a four channel Luttinger liquid theory can still be applied when SOI effects are taken into account. Compared to previous formulations, the low-energy Hamiltonian is characterized by different Luttinger parameters and plasmon velocities. Notably, the charge and spin modes are coupled. Our theory allows us to compute an asymptotically exact expression for the spectral function of a metallic carbon nanotube. We find modifications to the previously predicted structure of the spectral function that can in principle be tested by photoemission spectroscopy experiments. We develop a very similar low energy description for an interacting quantum wire subject to Rashba spin-orbit coupling (RSOC). We derive a two component Luttinger liquid Hamiltonian in the presence of RSOC, taking into account all e-e interaction processes allowed by the conservation of total momentum. The effective low energy Hamiltonian includes an additional perturbation due to intraband backscattering processes with band flip. Within a one-loop RG scheme, this perturbation is marginally irrelevant. The fixed point model is then still a two channel Luttinger liquid, albeit with a non standard form due to SOI. Again, the charge and spin mode are coupled. Using our low energy theory, we address the problem of the RKKY interaction in an interacting Rashba wire. The coupling of spin and charge modes due to SO effects implies several modifications, e.g. the explicit dependence of the power-law decay exponent of

Spin-orbit coupling effects, interactions and superconducting transport in nanostructures

International Nuclear Information System (INIS)

Schulz, Andreas

2010-05-01

In the present thesis we study the electronic properties of several low dimensional nanoscale systems. In the first part, we focus on the combined effect of spin-orbit coupling (SOI) and Coulomb interaction in carbon nanotubes (CNTs) as well as quantum wires. We derive low energy theories for both systems, using the bosonization technique and obtain analytic expressions for the correlation functions that allow us to compute basically all observables of interest. We first focus on CNTs and show that a four channel Luttinger liquid theory can still be applied when SOI effects are taken into account. Compared to previous formulations, the low-energy Hamiltonian is characterized by different Luttinger parameters and plasmon velocities. Notably, the charge and spin modes are coupled. Our theory allows us to compute an asymptotically exact expression for the spectral function of a metallic carbon nanotube. We find modifications to the previously predicted structure of the spectral function that can in principle be tested by photoemission spectroscopy experiments. We develop a very similar low energy description for an interacting quantum wire subject to Rashba spin-orbit coupling (RSOC). We derive a two component Luttinger liquid Hamiltonian in the presence of RSOC, taking into account all e-e interaction processes allowed by the conservation of total momentum. The effective low energy Hamiltonian includes an additional perturbation due to intraband backscattering processes with band flip. Within a one-loop RG scheme, this perturbation is marginally irrelevant. The fixed point model is then still a two channel Luttinger liquid, albeit with a non standard form due to SOI. Again, the charge and spin mode are coupled. Using our low energy theory, we address the problem of the RKKY interaction in an interacting Rashba wire. The coupling of spin and charge modes due to SO effects implies several modifications, e.g. the explicit dependence of the power-law decay exponent of

SPIN–SPIN COUPLING IN THE SOLAR SYSTEM

International Nuclear Information System (INIS)

Batygin, Konstantin; Morbidelli, Alessandro

2015-01-01

The richness of dynamical behavior exhibited by the rotational states of various solar system objects has driven significant advances in the theoretical understanding of their evolutionary histories. An important factor that determines whether a given object is prone to exhibiting non-trivial rotational evolution is the extent to which such an object can maintain a permanent aspheroidal shape, meaning that exotic behavior is far more common among the small body populations of the solar system. Gravitationally bound binary objects constitute a substantial fraction of asteroidal and TNO populations, comprising systems of triaxial satellites that orbit permanently deformed central bodies. In this work, we explore the rotational evolution of such systems with specific emphasis on quadrupole–quadrupole interactions, and show that for closely orbiting, highly deformed objects, both prograde and retrograde spin–spin resonances naturally arise. Subsequently, we derive capture probabilities for leading order commensurabilities and apply our results to the illustrative examples of (87) Sylvia and (216) Kleopatra asteroid systems. Cumulatively, our results suggest that spin–spin coupling may be consequential for highly elongated, tightly orbiting binary objects

SPIN–SPIN COUPLING IN THE SOLAR SYSTEM

Energy Technology Data Exchange (ETDEWEB)

Batygin, Konstantin [Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125 (United States); Morbidelli, Alessandro, E-mail: kbatygin@gps.caltech.edu [Departement Lagrange, Observatoire de la Côte d’Azur, F-06304 Nice (France)

2015-09-10

The richness of dynamical behavior exhibited by the rotational states of various solar system objects has driven significant advances in the theoretical understanding of their evolutionary histories. An important factor that determines whether a given object is prone to exhibiting non-trivial rotational evolution is the extent to which such an object can maintain a permanent aspheroidal shape, meaning that exotic behavior is far more common among the small body populations of the solar system. Gravitationally bound binary objects constitute a substantial fraction of asteroidal and TNO populations, comprising systems of triaxial satellites that orbit permanently deformed central bodies. In this work, we explore the rotational evolution of such systems with specific emphasis on quadrupole–quadrupole interactions, and show that for closely orbiting, highly deformed objects, both prograde and retrograde spin–spin resonances naturally arise. Subsequently, we derive capture probabilities for leading order commensurabilities and apply our results to the illustrative examples of (87) Sylvia and (216) Kleopatra asteroid systems. Cumulatively, our results suggest that spin–spin coupling may be consequential for highly elongated, tightly orbiting binary objects.

Induced spin-accumulation and spin-polarization in a quantum-dot ring by using magnetic quantum dots and Rashba spin-orbit effect

International Nuclear Information System (INIS)

Eslami, L.; Faizabadi, E.

2014-01-01

The effect of magnetic contacts on spin-dependent electron transport and spin-accumulation in a quantum ring, which is threaded by a magnetic flux, is studied. The quantum ring is made up of four quantum dots, where two of them possess magnetic structure and other ones are subjected to the Rashba spin-orbit coupling. The magnetic quantum dots, referred to as magnetic quantum contacts, are connected to two external leads. Two different configurations of magnetic moments of the quantum contacts are considered; the parallel and the anti-parallel ones. When the magnetic moments are parallel, the degeneracy between the transmission coefficients of spin-up and spin-down electrons is lifted and the system can be adjusted to operate as a spin-filter. In addition, the accumulation of spin-up and spin-down electrons in non-magnetic quantum dots are different in the case of parallel magnetic moments. When the intra-dot Coulomb interaction is taken into account, we find that the electron interactions participate in separation between the accumulations of electrons with different spin directions in non-magnetic quantum dots. Furthermore, the spin-accumulation in non-magnetic quantum dots can be tuned in the both parallel and anti-parallel magnetic moments by adjusting the Rashba spin-orbit strength and the magnetic flux. Thus, the quantum ring with magnetic quantum contacts could be utilized to create tunable local magnetic moments which can be used in designing optimized nanodevices.

Spin current and spin transfer torque in ferromagnet/superconductor spin valves

Science.gov (United States)

Moen, Evan; Valls, Oriol T.

2018-05-01

Using fully self-consistent methods, we study spin transport in fabricable spin valve systems consisting of two magnetic layers, a superconducting layer, and a spacer normal layer between the ferromagnets. Our methods ensure that the proper relations between spin current gradients and spin transfer torques are satisfied. We present results as a function of geometrical parameters, interfacial barrier values, misalignment angle between the ferromagnets, and bias voltage. Our main results are for the spin current and spin accumulation as functions of position within the spin valve structure. We see precession of the spin current about the exchange fields within the ferromagnets, and penetration of the spin current into the superconductor for biases greater than the critical bias, defined in the text. The spin accumulation exhibits oscillating behavior in the normal metal, with a strong dependence on the physical parameters both as to the structure and formation of the peaks. We also study the bias dependence of the spatially averaged spin transfer torque and spin accumulation. We examine the critical-bias effect of these quantities, and their dependence on the physical parameters. Our results are predictive of the outcome of future experiments, as they take into account imperfect interfaces and a realistic geometry.

Vanishing current hysteresis under competing nuclear spin pumping processes in a quadruplet spin-blockaded double quantum dot

Energy Technology Data Exchange (ETDEWEB)

Amaha, S., E-mail: s-amaha@riken.jp [Quantum Spin Information Project, Japan Science and Technology Agency, ICORP, 3-1, Morinosato Wakamiya, Atsugi-shi, Kanagawa 243-0198 (Japan); Quantum Functional System Research Group, RIKEN Center for Emergent Matter Science, RIKEN, 3-1 Wako-shi, Saitama 351-0198 (Japan); Hatano, T. [Quantum Spin Information Project, Japan Science and Technology Agency, ICORP, 3-1, Morinosato Wakamiya, Atsugi-shi, Kanagawa 243-0198 (Japan); Department of Physics, Tohoku University, Sendai-shi, Miyagi 980-8578 (Japan); Tarucha, S. [Quantum Spin Information Project, Japan Science and Technology Agency, ICORP, 3-1, Morinosato Wakamiya, Atsugi-shi, Kanagawa 243-0198 (Japan); Quantum Functional System Research Group, RIKEN Center for Emergent Matter Science, RIKEN, 3-1 Wako-shi, Saitama 351-0198 (Japan); Department of Applied Physics, School of Engineering, University of Tokyo, 7-3-1, Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan); Gupta, J. A.; Austing, D. G. [National Research Council of Canada, M50, Montreal Road, Ottawa, Ontario K1A 0R6 (Canada)

2015-04-27

We investigate nuclear spin pumping with five-electron quadruplet spin states in a spin-blockaded weakly coupled vertical double quantum dot device. Two types of hysteretic steps in the leakage current are observed on sweeping the magnetic field and are associated with bidirectional polarization of nuclear spin. Properties of the steps are understood in terms of bias-voltage-dependent conditions for the mixing of quadruplet and doublet spin states by the hyperfine interaction. The hysteretic steps vanish when up- and down-nuclear spin pumping processes are in close competition.

Double-spin-flip resonance of rhodium nuclei at positive and negative spin temperatures

DEFF Research Database (Denmark)

Tuoriniemi, J.T.; Knuuttila, T.A.; Lefmann, K.

2000-01-01

Sensitive SQUID-NMR measurements were used to study the mutual interactions in the highly polarized nuclear-spin system of rhodium metal. The dipolar coupling gives rise to a weak double-spin-flip resonance. The observed frequency shifts allow deducing separately the dipolarlike contribution...

Dynamics of spin-flip photon-assisted tunneling

NARCIS (Netherlands)

Braakman, F.R.; Danon, J.; Schreiber, L.R.; Wegscheider, W.; Vandersypen, L.M.K.

2014-01-01

We present time-resolved measurements of spin-flip photon-assisted tunneling and spin-flip relaxation in a doubly occupied double quantum dot. The photon-assisted excitation rate as a function of magnetic field indicates that spin-orbit coupling is the dominant mechanism behind the spin-flip under

Higher-spin algebras, holography and flat space

Energy Technology Data Exchange (ETDEWEB)

Sleight, C. [Max-Planck-Institut für Physik (Werner-Heisenberg-Institut),Föhringer Ring 6, D-80805 Munich (Germany); Université Libre de Bruxelles and International Solvay Institutes,ULB-Campus Plaine CP231, 1050 Brussels (Belgium); Taronna, M. [Université Libre de Bruxelles and International Solvay Institutes,ULB-Campus Plaine CP231, 1050 Brussels (Belgium)

2017-02-20

In this article we study the higher-spin algebra behind the type-A cubic couplings recently extracted from the free O(N) model in generic dimensions, demonstrating that they coincide with the known structure constants for the unique higher-spin algebra in generic dimensions. This provides an explicit check of the holographic reconstruction and of the duality between higher-spin theories and the free O(N) model in generic dimensions, generalising the result of Giombi and Yin in AdS{sub 4}. For completeness, we also address the same problem in the flat space for the cubic couplings derived by Metsaev in 1991, which are recovered from the flat limit of the AdS type-A cubic couplings. We observe that both flat and AdS{sub 4} higher-spin Lorentz subalgebras coincide, hinting towards the existence of a full higher-spin symmetry behind the flat-space cubic couplings of Metsaev.

Coupled intertwiner dynamics: A toy model for coupling matter to spin foam models

OpenAIRE

Steinhaus, Sebastian

2015-01-01

The universal coupling of matter and gravity is one of the most important features of general relativity. In quantum gravity, in particular spin foams, matter couplings have been defined in the past, yet the mutual dynamics, in particular if matter and gravity are strongly coupled, are hardly explored, which is related to the definition of both matter and gravitational degrees of freedom on the discretisation. However extracting this mutual dynamics is crucial in testing the viability of the ...

Experimental study on the spin-orbit coupling property in low-dimensional semiconductor structures

International Nuclear Information System (INIS)

Zhao, Hongming

2010-01-01

The spin-orbit coupling and optical properties have been studied in several low-dimensional semiconductor structures. First, the spin dynamics in (001) GaAs/AlGaAs two-dimensional electron gas was investigated by time resolved Kerr rotation technique under a transverse magnetic field. The in-plane spin lifetime is found to be anisotropic. The results show that the electron density in two-dimensional electron gas channel strongly affects the Rashba spin-orbit coupling. Then, a large anisotropy of the magnitude of in-plane conduction electron g factor in asymmetric (001) GaAs/AlGaAs QWs was observed and its tendency of temperature dependence was studied. Second, the experimental study of the in-plane-orientation dependent spin splitting in the C(0001) GaN/AlGaN two-dimensional electron gas at room temperature was reported. The measurement of circular photo-galvanic effect current clearly shows the isotropic in-plane spin splitting in this system for the first time. Third, the first measurement of conduction electron g factor in GaAsN at room temperature was done by using time resolved Kerr rotation technique. It demonstrates that the g factor can be modified drastically by introducing a small amount of nitrogen in GaAs bulk. Finally, the optical characteristic of indirect type II transition in a series of size and shape-controlled linear CdTe/CdSe/CdTe heterostructure nano-rods was studied by steady-state and time resolved photoluminescence. Results show the steady transfer from the direct optical transition (type I) within CdSe to the indirect transition (type II) between CdSe/CdTe as the length of the nano-rods increases. (author)

Spin transport in non-inertial frame

Energy Technology Data Exchange (ETDEWEB)

Chowdhury, Debashree, E-mail: debashreephys@gmail.com; Basu, B., E-mail: sribbasu@gmail.com

2014-09-01

The influence of acceleration and rotation on spintronic applications is theoretically investigated. In our formulation, considering a Dirac particle in a non-inertial frame, different spin related aspects are studied. The spin current appearing due to the inertial spin–orbit coupling (SOC) is enhanced by the interband mixing of the conduction and valence band states. Importantly, one can achieve a large spin current through the k{sup →}.p{sup →} method in this non-inertial frame. Furthermore, apart from the inertial SOC term due to acceleration, for a particular choice of the rotation frequency, a new kind of SOC term can be obtained from the spin rotation coupling (SRC). This new kind of SOC is of Dresselhaus type and controllable through the rotation frequency. In the field of spintronic applications, utilizing the inertial SOC and SRC induced SOC term, theoretical proposals for the inertial spin filter, inertial spin galvanic effect are demonstrated. Finally, one can tune the spin relaxation time in semiconductors by tuning the non-inertial parameters.

Spin-flip configuration interaction singles with exact spin-projection: Theory and applications to strongly correlated systems.

Science.gov (United States)

Tsuchimochi, Takashi

2015-10-14

Spin-flip approaches capture static correlation with the same computational scaling as the ordinary single reference methods. Here, we extend spin-flip configuration interaction singles (SFCIS) by projecting out intrinsic spin-contamination to make it spin-complete, rather than by explicitly complementing it with spin-coupled configurations. We give a general formalism of spin-projection for SFCIS, applicable to any spin states. The proposed method is viewed as a natural unification of SFCIS and spin-projected CIS to achieve a better qualitative accuracy at a low computational cost. While our wave function ansatz is more compact than previously proposed spin-complete SF approaches, it successfully offers more general static correlation beyond biradicals without sacrificing good quantum numbers. It is also shown that our method is invariant with respect to open-shell orbital rotations, due to the uniqueness of spin-projection. We will report benchmark calculations to demonstrate its qualitative performance on strongly correlated systems, including conical intersections that appear both in ground-excited and excited-excited degeneracies.

Electronic readout of a single nuclear spin using a molecular spin transistor

Science.gov (United States)

Vincent, R.; Klyastskaya, S.; Ruben, M.; Wernsdorfer, W.; Balestro, F.

2012-02-01

Quantum control of individual spins in condensed matter devices is an emerging field with a wide range of applications ranging from nanospintronics to quantum computing [1,2]. The electron, with its spin and orbital degrees of freedom, is conventionally used as carrier of the quantum information in the devices proposed so far. However, electrons exhibit a strong coupling to the environment leading to reduced relaxation and coherence times. Indeed quantum coherence and stable entanglement of electron spins are extremely difficult to achieve. We propose a new approach using the nuclear spin of an individual metal atom embedded in a single-molecule magnet (SMM). In order to perform the readout of the nuclear spin, the quantum tunneling of the magnetization (QTM) of the magnetic moment of the SMM in a transitor-like set-up is electronically detected. Long spin lifetimes of an individual nuclear spin were observed and the relaxation characteristics were studied. The manipulation of the nuclear spin state of individual atoms embedded in magnetic molecules opens a completely new world, where quantum logic may be integrated.[4pt] [1] L. Bogani, W. Wernsdorfer, Nature Mat. 7, 179 (2008).[0pt] [2] M. Urdampilleta, S. Klyatskaya, J.P. Cleuziou, M. Ruben, W. Wernsdorfer, Nature Mat. 10, 502 (2011).

A controllable spin prism

International Nuclear Information System (INIS)

Hakioglu, T

2009-01-01

Based on Khodas et al (2004 Phys. Rev. Lett. 92 086602), we propose a device acting like a controllable prism for an incident spin. The device is a large quantum well where Rashba and Dresselhaus spin-orbit interactions are present and controlled by the plunger gate potential, the electric field and the barrier height. A totally destructive interference can be manipulated externally between the Rashba and Dresselhaus couplings. The spin-dependent transmission/reflection amplitudes are calculated as the control parameters are changed. The device operates as a spin prism/converter/filter in different regimes and may stimulate research in promising directions in spintronics in analogy with linear optics.

Spin-photon entangling diode

DEFF Research Database (Denmark)

Flindt, Christian; Sørensen, A. S.; Lukin, M. D.

2007-01-01

We propose a semiconductor device that can electrically generate entangled electron spin-photon states, providing a building block for entanglement of distant spins. The device consists of a p-i-n diode structure that incorporates a coupled double quantum dot. We show that electronic control of t...

Nuclear spins in nanostructures

International Nuclear Information System (INIS)

Coish, W.A.; Baugh, J.

2009-01-01

We review recent theoretical and experimental advances toward understanding the effects of nuclear spins in confined nanostructures. These systems, which include quantum dots, defect centers, and molecular magnets, are particularly interesting for their importance in quantum information processing devices, which aim to coherently manipulate single electron spins with high precision. On one hand, interactions between confined electron spins and a nuclear-spin environment provide a decoherence source for the electron, and on the other, a strong effective magnetic field that can be used to execute local coherent rotations. A great deal of effort has been directed toward understanding the details of the relevant decoherence processes and to find new methods to manipulate the coupled electron-nuclear system. A sequence of spectacular new results have provided understanding of spin-bath decoherence, nuclear spin diffusion, and preparation of the nuclear state through dynamic polarization and more general manipulation of the nuclear-spin density matrix through ''state narrowing.'' These results demonstrate the richness of this physical system and promise many new mysteries for the future. (Abstract Copyright [2009], Wiley Periodicals, Inc.)

Spin-orbit torques in magnetic bilayers

Science.gov (United States)

Haney, Paul

2015-03-01

Spintronics aims to utilize the coupling between charge transport and magnetic dynamics to develop improved and novel memory and logic devices. Future progress in spintronics may be enabled by exploiting the spin-orbit coupling present at the interface between thin film ferromagnets and heavy metals. In these systems, applying an in-plane electrical current can induce magnetic dynamics in single domain ferromagnets, or can induce rapid motion of domain wall magnetic textures. There are multiple effects responsible for these dynamics. They include spin-orbit torques and a chiral exchange interaction (the Dzyaloshinskii-Moriya interaction) in the ferromagnet. Both effects arise from the combination of ferromagnetism and spin-orbit coupling present at the interface. There is additionally a torque from the spin current flux impinging on the ferromagnet, arising from the spin hall effect in the heavy metal. Using a combination of approaches, from drift-diffusion to Boltzmann transport to first principles methods, we explore the relative contributions to the dynamics from these different effects. We additionally propose that the transverse spin current is locally enhanced over its bulk value in the vicinity of an interface which is oriented normal to the charge current direction.

Polarization of nuclear spins by a cold nanoscale resonator

International Nuclear Information System (INIS)

Butler, Mark C.; Weitekamp, Daniel P.

2011-01-01

A cold nanoscale resonator coupled to a system of nuclear spins can induce spin relaxation. In the low-temperature limit where spin-lattice interactions are ''frozen out,'' spontaneous emission by nuclear spins into a resonant mechanical mode can become the dominant mechanism for cooling the spins to thermal equilibrium with their environment. We provide a theoretical framework for the study of resonator-induced cooling of nuclear spins in this low-temperature regime. Relaxation equations are derived from first principles, in the limit where energy donated by the spins to the resonator is quickly dissipated into the cold bath that damps it. A physical interpretation of the processes contributing to spin polarization is given. For a system of spins that have identical couplings to the resonator, the interaction Hamiltonian conserves spin angular momentum, and the resonator cannot relax the spins to thermal equilibrium unless this symmetry is broken by the spin Hamiltonian. The mechanism by which such a spin system becomes ''trapped'' away from thermal equilibrium can be visualized using a semiclassical model, which shows how an indirect spin-spin interaction arises from the coupling of multiple spins to one resonator. The internal spin Hamiltonian can affect the polarization process in two ways: (1) By modifying the structure of the spin-spin correlations in the energy eigenstates, and (2) by splitting the degeneracy within a manifold of energy eigenstates, so that zero-frequency off-diagonal terms in the density matrix are converted to oscillating coherences. Shifting the frequencies of these coherences sufficiently far from zero suppresses the development of resonator-induced correlations within the manifold during polarization from a totally disordered state. Modification of the spin-spin correlations by means of either mechanism affects the strength of the fluctuating spin dipole that drives the resonator. In the case where product states can be chosen as energy

Rashba and Dresselhaus Couplings in Halide Perovskites: Accomplishments and Opportunities for Spintronics and Spin-Orbitronics.

Science.gov (United States)

Kepenekian, Mikaël; Even, Jacky

2017-07-20

In halide hybrid organic-inorganic perovskites (HOPs), spin-orbit coupling (SOC) presents a well-documented large influence on band structure. However, SOC may also present more exotic effects, such as Rashba and Dresselhaus couplings. In this Perspective, we start by recalling the main features of this effect and what makes HOP materials ideal candidates for the generation and tuning of spin-states. Then, we detail the main spectroscopy techniques able to characterize these effects and their application to HOPs. Finally, we discuss potential applications in spintronics and in spin-orbitronics in those nonmagnetic systems, which would complete the skill set of HOPs and perpetuate their ride on the crest of the wave of popularity started with optoelectronics and photovoltaics.

Spin-polarized currents in a two-terminal double quantum ring driven by magnetic fields and Rashba spin-orbit interaction

Science.gov (United States)

Dehghan, E.; Khoshnoud, D. Sanavi; Naeimi, A. S.

2018-06-01

Aim of this study is to investigate spin transportation in double quantum ring (DQR). We developed an array of DQR to measure the transmission coefficient and analyze the spin transportation through this system in the presence of Rashba spin-orbit interaction (RSOI) and magnetic flux estimated using S-matrix method. In this article, we compute the spin transport and spin-current characteristics numerically as functions of electron energy, angles between the leads, coupling constant of the leads, RSOI, and magnetic flux. Our results suggest that, for typical values of the magnetic flux (ϕ /ϕ0) and Rashba constant (αR), such system can demonstrates many spintronic properties. It is possible to design a new geometry of DQR by incoming electrons polarization in a way to optimize the system to work as a spin-filtering and spin-inverting nano-device with very high efficiency. The results prove that the spin current will strongly modulate with an increase in the magnetic flux and Rashba constant. Moreover it is shown that, when the lead coupling is weak, the perfect spin-inverter does not occur.

Modeling of diffusion of injected electron spins in spin-orbit coupled microchannels

Czech Academy of Sciences Publication Activity Database

Zarbo, Liviu; Sinova, Jairo; Knezevic, I.; Wunderlich, Joerg; Jungwirth, Tomáš

2010-01-01

Roč. 82, č. 20 (2010), 205320/1-205320/7 ISSN 1098-0121 R&D Projects: GA MŠk LC510; GA AV ČR KAN400100652 EU Projects: European Commission(XE) 215368 - SemiSpinNet Grant - others:AV ČR(CZ) AP0801 Program:Akademická prémie - Praemium Academiae Institutional research plan: CEZ:AV0Z10100521 Keywords : spintronics * spin dynamics Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.772, year: 2010

Anisotropic intrinsic spin Hall effect in quantum wires

International Nuclear Information System (INIS)

Cummings, A W; Akis, R; Ferry, D K

2011-01-01

We use numerical simulations to investigate the spin Hall effect in quantum wires in the presence of both Rashba and Dresselhaus spin-orbit coupling. We find that the intrinsic spin Hall effect is highly anisotropic with respect to the orientation of the wire, and that the nature of this anisotropy depends strongly on the electron density and the relative strengths of the Rashba and Dresselhaus spin-orbit couplings. In particular, at low densities, when only one subband of the quantum wire is occupied, the spin Hall effect is strongest for electron momentum along the [1-bar 10] axis, which is the opposite of what is expected for the purely 2D case. In addition, when more than one subband is occupied, the strength and anisotropy of the spin Hall effect can vary greatly over relatively small changes in electron density, which makes it difficult to predict which wire orientation will maximize the strength of the spin Hall effect. These results help to illuminate the role of quantum confinement in spin-orbit-coupled systems, and can serve as a guide for future experimental work on the use of quantum wires for spin-Hall-based spintronic applications. (paper)

Magnetism of one-dimensional strongly repulsive spin-1 bosons with antiferromagnetic spin-exchange interaction

International Nuclear Information System (INIS)

Lee, J. Y.; Guan, X. W.; Batchelor, M. T.; Lee, C.

2009-01-01

We investigate magnetism and quantum phase transitions in a one-dimensional system of integrable spin-1 bosons with strongly repulsive density-density interaction and antiferromagnetic spin-exchange interaction via the thermodynamic Bethe ansatz method. At zero temperature, the system exhibits three quantum phases: (i) a singlet phase of boson pairs when the external magnetic field H is less than the lower critical field H c1 ; (ii) a ferromagnetic phase of atoms in the hyperfine state |F=1, m F =1> when the external magnetic field exceeds the upper critical field H c2 ; and (iii) a mixed phase of singlet pairs and unpaired atoms in the intermediate region H c1 c2 . At finite temperatures, the spin fluctuations affect the thermodynamics of the model through coupling the spin bound states to the dressed energy for the unpaired m F =1 bosons. However, such spin dynamics is suppressed by a sufficiently strong external field at low temperatures. Thus the singlet pairs and unpaired bosons may form a two-component Luttinger liquid in the strong coupling regime.

Spin-orbit splitted excited states using explicitly-correlated equation-of-motion coupled-cluster singles and doubles eigenvectors

Science.gov (United States)

Bokhan, Denis; Trubnikov, Dmitrii N.; Perera, Ajith; Bartlett, Rodney J.

2018-04-01

An explicitly-correlated method of calculation of excited states with spin-orbit couplings, has been formulated and implemented. Developed approach utilizes left and right eigenvectors of equation-of-motion coupled-cluster model, which is based on the linearly approximated explicitly correlated coupled-cluster singles and doubles [CCSD(F12)] method. The spin-orbit interactions are introduced by using the spin-orbit mean field (SOMF) approximation of the Breit-Pauli Hamiltonian. Numerical tests for several atoms and molecules show good agreement between explicitly-correlated results and the corresponding values, calculated in complete basis set limit (CBS); the highly-accurate excitation energies can be obtained already at triple- ζ level.

Spin force and the generation of sustained spin current in time-dependent Rashba and Dresselhaus systems

International Nuclear Information System (INIS)

Ho, Cong Son; Tan, Seng Ghee; Jalil, Mansoor B. A.

2014-01-01

The generation of spin current and spin polarization in a two-dimensional electron gas structure is studied in the presence of Dresselhaus and Rashba spin-orbit couplings (SOC), the strength of the latter being modulated in time by an ac gate voltage. By means of the non-Abelian gauge field approach, we established the relation between the Lorentz spin force and the spin current in the SOC system, and showed that the longitudinal component of the spin force induces a transverse spin current. For a constant (time-invariant) Rashba system, we recover the universal spin Hall conductivity of e/(8π) , derived previously via the Berry phase and semi-classical methods. In the case of a time-dependent SOC system, the spin current is sustained even under strong impurity scattering. We evaluated the ac spin current generated by a time-modulated Rashba SOC in the absence of any dc electric field. The magnitude of the spin current reaches a maximum when the modulation frequency matches the Larmor frequency of the electrons

The spin-spin effect in the total neutron cross section of polarized neutrons on polarized 165Ho

International Nuclear Information System (INIS)

Fasoli, U.; Galeazzi, G.; Pavan, P.; Toniolo, D.; Zago, G.; Zannoni, R.

1978-01-01

The spin-spin effect in the total neutron cross section of polarized neutrons on polarized 165 Ho has been measured in the energy interval 0.4 to 2.5 MeV, in perpendicular geometry. The results are consistent with zero effect. The spin-spin cross section sigmasub(ss) has been theoretically evaluated by a non-adiabatic coupled-channel calculation. From the comparison between the experimental and theoretical results a value Vsub(ss) = 9+-77 keV for the strength of the spin-spin potential has been obtained. Compound-nucleus effects do not seem to be relevant. (Auth.)

Tailoring spin-orbit torque in diluted magnetic semiconductors

KAUST Repository

Li, Hang; Wang, Xuhui; Doǧan, Fatih; Manchon, Aurelien

2013-01-01

We study the spin orbit torque arising from an intrinsic linear Dresselhaus spin-orbit coupling in a single layer III-V diluted magnetic semiconductor. We investigate the transport properties and spin torque using the linear response theory, and we report here: (1) a strong correlation exists between the angular dependence of the torque and the anisotropy of the Fermi surface; (2) the spin orbit torque depends nonlinearly on the exchange coupling. Our findings suggest the possibility to tailor the spin orbit torque magnitude and angular dependence by structural design.

Tailoring spin-orbit torque in diluted magnetic semiconductors

KAUST Repository

Li, Hang

2013-05-16

We study the spin orbit torque arising from an intrinsic linear Dresselhaus spin-orbit coupling in a single layer III-V diluted magnetic semiconductor. We investigate the transport properties and spin torque using the linear response theory, and we report here: (1) a strong correlation exists between the angular dependence of the torque and the anisotropy of the Fermi surface; (2) the spin orbit torque depends nonlinearly on the exchange coupling. Our findings suggest the possibility to tailor the spin orbit torque magnitude and angular dependence by structural design.

Geometric phase of a central spin coupled to an antiferromagnetic environment

International Nuclear Information System (INIS)

Yuan Xiaozhong; Zhu Kadi; Goan, H.-S.

2010-01-01

Using the spin-wave approximation, we study the geometric phase (GP) of a central spin (signal qubit) coupled to an antiferromagnetic (AF) environment under the application of an external global magnetic field. The external magnetic field affects the GP of the qubit directly and also indirectly through its effect on the AF environment. We find that when the applied magnetic field is increased to the critical magnetic field point, the AF environment undergoes a spin-flop transition, a first-order phase transition, and at the same time the GP of the qubit changes abruptly to zero. This sensitive change of the GP of a signal qubit to the parameter change of a many-body environment near its critical point may serve as another efficient tool or witness to study the many-body phase transition. The influences of the AF environment temperature and crystal anisotropy field on the GP are also investigated.

Crossover between spin swapping and Hall effect in disordered systems

KAUST Repository

Saidaoui, Hamed Ben Mohamed

2015-07-16

We theoretically study the crossover between spin Hall effect and spin swapping, a recently predicted phenomenon that consists of the interchange between the current flow and its spin polarization directions [M. B. Lifshits and M. I. Dyakonov, Phys. Rev. Lett. 103, 186601 (2009)]. Using a tight-binding model with spin-orbit coupled disorder, spin Hall effect, spin relaxation, and spin swapping are treated on equal footing. We demonstrate that spin swapping and spin Hall effect present very different dependencies as a function of the spin-orbit coupling and disorder strengths and confirm that the former exceeds the latter in the parameter range considered. Three setups are proposed for the experimental observation of the spin swapping effect.

Crossover between spin swapping and Hall effect in disordered systems

KAUST Repository

Saidaoui, Hamed Ben Mohamed; Otani, Y.; Manchon, Aurelien

2015-01-01

We theoretically study the crossover between spin Hall effect and spin swapping, a recently predicted phenomenon that consists of the interchange between the current flow and its spin polarization directions [M. B. Lifshits and M. I. Dyakonov, Phys. Rev. Lett. 103, 186601 (2009)]. Using a tight-binding model with spin-orbit coupled disorder, spin Hall effect, spin relaxation, and spin swapping are treated on equal footing. We demonstrate that spin swapping and spin Hall effect present very different dependencies as a function of the spin-orbit coupling and disorder strengths and confirm that the former exceeds the latter in the parameter range considered. Three setups are proposed for the experimental observation of the spin swapping effect.

Acoustic parametric pumping of spin waves

Science.gov (United States)

Keshtgar, Hedyeh; Zareyan, Malek; Bauer, Gerrit E. W.

2014-11-01

Recent experiments demonstrated generation of spin currents by ultrasound. We can understand this acoustically induced spin pumping in terms of the coupling between magnetization and lattice waves. Here we study the parametric excitation of magnetization by longitudinal acoustic waves and calculate the acoustic threshold power. The induced magnetization dynamics can be detected by the spin pumping into an adjacent normal metal that displays the inverse spin Hall effect.

Acoustic parametric pumping of spin waves

OpenAIRE

Keshtgar, Hedyeh; Zareyan, Malek; Bauer, Gerrit E. W.

2013-01-01

Recent experiments demonstrated generation of spin currents by ultrasound. We can understand this acoustically induced spin pumping in terms of the coupling between magnetization and lattice waves. Here we study the parametric excitation of magnetization by longitudinal acoustic waves and calculate the acoustic threshold power. The induced magnetization dynamics can be detected by the spin pumping into an adjacent normal metal that displays the inverse spin Hall effect.

Spin current evolution in the separated spin-up and spin-down quantum hydrodynamics

International Nuclear Information System (INIS)

Trukhanova, Mariya Iv.

2015-01-01

We have developed a method of quantum hydrodynamics (QHD) that describes particles with spin-up and with spin-down in separate. We have derived the equation of the spin current evolution as a part of the set of the quantum hydrodynamics equations that treat particles with different projection of spin on the preferable direction as two different species. We have studied orthogonal propagation of waves in the external magnetic field and determined the contribution of quantum corrections due to the Bohm potential and to magnetization energy of particles with different projections of spin in the spin-current wave dispersion. We have analyzed the limits of weak and strong magnetic fields. - Highlights: • We derive the spin current equation for particles with different projection of spin. • We predict the contribution of Bohm potential to the dynamics of spin current. • We derive the spin-current wave in the system of spin-polarized particles. • We study the propagation of spin-acoustic wave in magnetized dielectrics.

Breakdown of Spin-Waves in Anisotropic Magnets: Spin Dynamics in α-RuCl3

Science.gov (United States)

Winter, Stephen; Riedl, Kira; Honecker, Andreas; Valenti, Roser

α -RuCl3 has recently emerged as a promising candidate for realizing the hexagonal Kitaev model in a real material. Similar to the related iridates (e.g. Na2IrO3), complex magnetic interactions arise from a competition between various similar energy scales, including spin-orbit coupling (SOC), Hund's coupling, and crystal-field splitting. Due to this complexity, the correct spin Hamiltonians for such systems remain hotly debated. For α-RuCl3, a combination of ab-initio calculations, microscopic considerations, and analysis of the static magnetic response have suggested off-diagonal couplings (Γ ,Γ') and long-range interactions in addition to the expected Kitaev exchange. However, the effect of such additional terms on the dynamic response remains unclear. In this contribution, we discuss the recently measured inelastic neutron scattering response in the context of realistic proposals for the microscopic spin Hamiltonian. We conclude that the observed scattering continuum, which has been taken as a signature of Kitaev spin liquid physics, likely persists over a broad range of parameters.

Muonium spin exchange in spin-polarized media: Spin-flip and -nonflip collisions

International Nuclear Information System (INIS)

Senba, M.

1994-01-01

The transverse relaxation of the muon spin in muonium due to electron spin exchange with a polarized spin-1/2 medium is investigated. Stochastic calculations, which assume that spin exchange is a Poisson process, are carried out for the case where the electron spin polarization of the medium is on the same axis as the applied field. Two precession signals of muonium observed in intermediate fields (B>30 G) are shown to have different relaxation rates which depend on the polarization of the medium. Furthermore, the precession frequencies are shifted by an amount which depends on the spin-nonflip rate. From the two relaxation rates and the frequency shift in intermediate fields, one can determine (i) the encounter rate of muonium and the paramagnetic species, (ii) the polarization of the medium, and most importantly (iii) the quantum-mechanical phase shift (and its sign) associated with the potential energy difference between electron singlet and triplet encounters. Effects of spin-nonflip collisions on spin dynamics are discussed for non-Poisson as well as Poisson processes. In unpolarized media, the time evolution of the muon spin in muonium is not influenced by spin-nonflip collisions, if the collision process is Poissonian. This seemingly obvious statement is not true anymore in non-Poissonian processes, i.e., it is necessary to specify both spin-flip and spin-nonflip rates to fully characterize spin dynamics

Spin orbit coupling for molecular ab initio density matrix renormalization group calculations: Application to g-tensors

Energy Technology Data Exchange (ETDEWEB)

Roemelt, Michael, E-mail: michael.roemelt@theochem.rub.de [Lehrstuhl für Theoretische Chemie, Ruhr-Universität Bochum, D-44780 Bochum, Germany and Max-Planck Institut für Kohlenforschung, Kaiser-Wilhelm-Platz 1, 45470 Mülheim an der Ruhr (Germany)

2015-07-28

Spin Orbit Coupling (SOC) is introduced to molecular ab initio density matrix renormalization group (DMRG) calculations. In the presented scheme, one first approximates the electronic ground state and a number of excited states of the Born-Oppenheimer (BO) Hamiltonian with the aid of the DMRG algorithm. Owing to the spin-adaptation of the algorithm, the total spin S is a good quantum number for these states. After the non-relativistic DMRG calculation is finished, all magnetic sublevels of the calculated states are constructed explicitly, and the SOC operator is expanded in the resulting basis. To this end, spin orbit coupled energies and wavefunctions are obtained as eigenvalues and eigenfunctions of the full Hamiltonian matrix which is composed of the SOC operator matrix and the BO Hamiltonian matrix. This treatment corresponds to a quasi-degenerate perturbation theory approach and can be regarded as the molecular equivalent to atomic Russell-Saunders coupling. For the evaluation of SOC matrix elements, the full Breit-Pauli SOC Hamiltonian is approximated by the widely used spin-orbit mean field operator. This operator allows for an efficient use of the second quantized triplet replacement operators that are readily generated during the non-relativistic DMRG algorithm, together with the Wigner-Eckart theorem. With a set of spin-orbit coupled wavefunctions at hand, the molecular g-tensors are calculated following the scheme proposed by Gerloch and McMeeking. It interprets the effective molecular g-values as the slope of the energy difference between the lowest Kramers pair with respect to the strength of the applied magnetic field. Test calculations on a chemically relevant Mo complex demonstrate the capabilities of the presented method.

One and two-phonon processes of the spin-flip relaxation in quantum dots: Spin-phonon coupling mechanism

Science.gov (United States)

Wang, Zi-Wu; Li, Shu-Shen

2012-07-01

We investigate the spin-flip relaxation in quantum dots using a non-radiation transition approach based on the descriptions for the electron-phonon deformation potential and Fröhlich interaction in the Pavlov-Firsov spin-phonon Hamiltonian. We give the comparisons of the electron relaxations with and without spin-flip assisted by one and two-phonon processes. Calculations are performed for the dependence of the relaxation time on the external magnetic field, the temperature and the energy separation between the Zeeman sublevels of the ground and first-excited state. We find that the electron relaxation time of the spin-flip process is more longer by three orders of magnitudes than that of no spin-flip process.

Solvent Effects on Nuclear Magnetic Resonance 2J(C,Hf and 1J(C,Hf Spin–Spin Coupling Constants in Acetaldehyde

Directory of Open Access Journals (Sweden)

Angel Esteban

2003-02-01

Full Text Available Abstract: The known solvent dependence of 1J(Cc,Hf and 2J(C1,Hf couplings in acetaldehyde is studied from a theoretical viewpoint based on the density functional theory approach where the dielectric solvent effect is taken into account with the polarizable continuum model. The four terms of scalar couplings, Fermi contact, paramagnetic spin orbital, diamagnetic spin orbital and spin dipolar, are calculated but the solvent effect analysis is restricted to the first term since for both couplings it is by far the dominant contribution. Experimental trends of Δ1J(Cc,Hf and Δ2J(C1,Hf Vs ε (the solvent dielectric constant are correctly reproduced although they are somewhat underestimated. Specific interactions between solute and solvent molecules are studied for dimethylsulfoxide, DMSO, solutions considering two different one-to-one molecular complexes between acetaldehyde and DMSO. They are determined by interactions of type C=O---H---C and S=O---H---C, and the effects of such interactions on 1J(Cc,Hf and 2J(C1,Hf couplings are analyzed. Even though only in a semiquantitative way, it is shown that the effect of such interactions on the solvent effects, of Δ1J(Cc,Hf and Δ2J(C1,Hf, tend to improve the agreement between calculated and experimental values. These results seem to indicate that a continuum dielectric model has not enough flexibility for describing quantitatively solvent effects on spin-spin couplings. Apparently, even for relatively weak hydrogen bonding, the contribution from “direct” interactions is of the same order of magnitude as the “dielectric” effect.

Neutron spin quantum precession using multilayer spin splitters and a phase-spin echo interferometer

International Nuclear Information System (INIS)

Ebisawa, Toru; Tasaki, Seiji; Kawai, Takeshi; Hino, Masahiro; Akiyoshi, Tsunekazu; Achiwa, Norio; Otake, Yoshie; Funahashi, Haruhiko.

1996-01-01

Neutron spin quantum precession by multilayer spin splitter has been demonstrated using a new spin interferometer. The multilayer spin splitter consists of a magnetic multilayer mirror on top, followed by a gap layer and a non magnetic multilayer mirror which are evaporated on a silicon substrate. Using the multilayer spin splitter, a polarized neutron wave in a magnetic field perpendicular to the polarization is split into two spin eigenstates with a phase shift in the direction of the magnetic field. The spin quantum precession is equal to the phase shift, which depends on the effective thickness of the gap layer. The demonstration experiments verify the multilayer spin splitter as a neutron spin precession device as well as the coherent superposition principle of the two spin eigenstates. We have developed a new phase-spin echo interferometer using the multilayer spin splitters. We present successful performance tests of the multilayer spin splitter and the phase-spin echo interferometer. (author)

Max Auwaerter symposium: spin mapping and spin manipulation on the atomic scale

International Nuclear Information System (INIS)

Wiesendanger, R.

2008-01-01

Full text: A fundamental understanding of magnetic and spin-dependent phenomena requires the determination of spin structures and spin excitations down to the atomic scale. The direct visualization of atomic-scale spin structures has first been accomplished for magnetic metals by combining the atomic resolution capability of Scanning Tunnelling Microscopy (STM) with spin sensitivity, based on vacuum tunnelling of spin-polarized electrons. The resulting technique, Spin-Polarized Scanning Tunnelling Microscopy (SP-STM), nowadays provides unprecedented insight into collinear and non-collinear spin structures at surfaces of magnetic nanostructures and has already led to the discovery of new types of magnetic order at the nanoscale. More recently, the development of subkelvin SP-STM has allowed studies of ground-state magnetic properties of individual magnetic adatoms on non-magnetic substrates as well as the magnetic interactions between them. Based on SP-STM experiments performed at temperatures of 300 mK, indirect magnetic exchange interactions at the sub-milli-electronvolt energy scale between individual paramagnetic adatoms as well as between adatoms and nearby magnetic nanostructures could directly be revealed in real space up to distances of several nanometers. In both cases we have observed an oscillatory behavior of the magnetic exchange coupling, alternating between ferromagnetic and antiferromagnetic, as a function of distance. Moreover, the detection of spin-dependent exchange and correlation forces has allowed a first direct real-space observation of spin structures at surfaces of antiferromagnetic insulators. This new type of scanning probe microscopy, called Magnetic Exchange Force Microscopy (MExFM), offers a powerful new tool to investigate different types of spin-spin interactions based on direct-, super-, or RKKY-type exchange down to the atomic level. By combining MExFM with high-precision measurements of damping forces, localized or confined spin

Spin Injection in Indium Arsenide

Directory of Open Access Journals (Sweden)

Mark eJohnson

2015-08-01

Full Text Available In a two dimensional electron system (2DES, coherent spin precession of a ballistic spin polarized current, controlled by the Rashba spin orbit interaction, is a remarkable phenomenon that’s been observed only recently. Datta and Das predicted this precession would manifest as an oscillation in the source-drain conductance of the channel in a spin-injected field effect transistor (Spin FET. The indium arsenide single quantum well materials system has proven to be ideal for experimental confirmation. The 2DES carriers have high mobility, low sheet resistance, and high spin orbit interaction. Techniques for electrical injection and detection of spin polarized carriers were developed over the last two decades. Adapting the proposed Spin FET to the Johnson-Silsbee nonlocal geometry was a key to the first experimental demonstration of gate voltage controlled coherent spin precession. More recently, a new technique measured the oscillation as a function of channel length. This article gives an overview of the experimental phenomenology of the spin injection technique. We then review details of the application of the technique to InAs single quantum well (SQW devices. The effective magnetic field associated with Rashba spin-orbit coupling is described, and a heuristic model of coherent spin precession is presented. The two successful empirical demonstrations of the Datta Das conductance oscillation are then described and discussed.

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.

Spin resonance with trapped ions

Energy Technology Data Exchange (ETDEWEB)

Wunderlich, Ch; Balzer, Ch; Hannemann, T; Mintert, F; Neuhauser, W; Reiss, D; Toschek, P E [Institut fuer Laser-Physik, Universitaet Hamburg, Jungiusstrasse 9, 20355 Hamburg (Germany)

2003-03-14

A modified ion trap is described where experiments (in particular related to quantum information processing) that usually require optical radiation can be carried out using microwave or radio frequency electromagnetic fields. Instead of applying the usual methods for coherent manipulation of trapped ions, a string of ions in such a modified trap can be treated like a molecule in nuclear magnetic resonance experiments taking advantage of spin-spin coupling. The collection of trapped ions can be viewed as an N-qubit molecule with adjustable spin-spin coupling constants. Given N identically prepared quantum mechanical two-level systems (qubits), the optimal strategy to estimate their quantum state requires collective measurements. Using the ground state hyperfine levels of electrodynamically trapped {sup 171}Yb{sup +}, we have implemented an adaptive algorithm for state estimation involving sequential measurements on arbitrary qubit states.

Spin resonance with trapped ions

International Nuclear Information System (INIS)

Wunderlich, Ch; Balzer, Ch; Hannemann, T; Mintert, F; Neuhauser, W; Reiss, D; Toschek, P E

2003-01-01

A modified ion trap is described where experiments (in particular related to quantum information processing) that usually require optical radiation can be carried out using microwave or radio frequency electromagnetic fields. Instead of applying the usual methods for coherent manipulation of trapped ions, a string of ions in such a modified trap can be treated like a molecule in nuclear magnetic resonance experiments taking advantage of spin-spin coupling. The collection of trapped ions can be viewed as an N-qubit molecule with adjustable spin-spin coupling constants. Given N identically prepared quantum mechanical two-level systems (qubits), the optimal strategy to estimate their quantum state requires collective measurements. Using the ground state hyperfine levels of electrodynamically trapped 171 Yb + , we have implemented an adaptive algorithm for state estimation involving sequential measurements on arbitrary qubit states

MODELING AND ANALYSIS OF COUPLED FLEXURAL-TORSIONAL SPINNING BEAMS WITH UNSYMMETRICAL CROSS SECTIONS

OpenAIRE

Wang, Jie; Li, Dongxu; Jiang, Jianping

2017-01-01

The structural modeling and dynamic properties of a spinning beam with an unsymmetrical cross section are studied. Due to the eccentricity and spinning, transverse deflections along the two principal directions and the torsional motion about the longitudinal axis are coupled. The structural model of the beam is established based on the Hamilton principle and by incorporating the torsional inertia. Moreover, because of its significant influence on characteristics for the non-circular cross-sec...

Theory of electrically controlled resonant tunneling spin devices

Science.gov (United States)

Ting, David Z. -Y.; Cartoixa, Xavier

2004-01-01

We report device concepts that exploit spin-orbit coupling for creating spin polarized current sources using nonmagnetic semiconductor resonant tunneling heterostructures, without external magnetic fields. The resonant interband tunneling psin filter exploits large valence band spin-orbit interaction to provide strong spin selectivity.

The Rashba spin-orbit coupling for superconductivity in oxide interfaces

Energy Technology Data Exchange (ETDEWEB)

Beyl, Stefan; Orth, Peter P.; Schmalian, Joerg [Institut fuer Theorie der Kondensierten Materie, Karlsruher Institut fuer Technologie, Karlsruhe (Germany)

2014-07-01

We investigate the role of the Rashba spin-orbit coupling on the superconducting order parameter and the phase stiffness at the interface of LaAlO{sub 3} and SrTiO{sub 3}. In particular, we analyze the gate controlled crossover between BCS superconductivity and Bose-Einstein condensation of Cooper pairs, amplified by the Rashba coupling and the possibility of a phase fluctuation induced quantum critical point.

Bulk magnon spin current theory for the longitudinal spin Seebeck effect

Energy Technology Data Exchange (ETDEWEB)

Rezende, S.M., E-mail: rezende@df.ufpe.br [Departamento de Física, Universidade Federal de Pernambuco, 50670-901 Recife, Pernambuco (Brazil); Rodríguez-Suárez, R.L. [Departamento de Física, Universidade Federal de Pernambuco, 50670-901 Recife, Pernambuco (Brazil); Facultad de Física, Pontificia Universidad Católica de Chile, Casilla, 306 Santiago (Chile); Cunha, R.O.; López Ortiz, J.C.; Azevedo, A. [Departamento de Física, Universidade Federal de Pernambuco, 50670-901 Recife, Pernambuco (Brazil)

2016-02-15

The longitudinal spin Seebeck effect (LSSE) consists in the generation of a spin current parallel to a temperature gradient applied across the thickness of a bilayer made of a ferromagnetic insulator (FMI), such as yttrium iron garnet (YIG), and a metallic layer (ML) with strong spin orbit coupling, such as platinum. The LSSE is usually detected by a DC voltage generated along the ML due to the conversion of the spin current into a charge current perpendicular to the static magnetic field by means of the inverse spin Hall effect. Here we present a model for the LSSE that relies on the bulk magnon spin current created by the temperature gradient across the thickness of the FMI. We show that the spin current pumped into the metallic layer by the magnon accumulation in the FMI provides continuity of the spin current at the FMI/ML interface and is essential for the existence of the LSSE. The results of the theory are in good agreement with experimental LSSE data in YIG/Pt bilayers on the variation of the DC voltage with the sample temperature, with the FMI layer thickness and with the intensity of high magnetic fields. - Highlights: • We present a theory for the longitudinal spin Seebeck effect based on bulk magnons. • The model explains quantitatively the measured voltage in YIG/Pt created by the LSSE. • The model explains quantitatively the temperature dependence of LSSE measured in YIG/Pt. • The model agrees qualitatively with the measured dependence of LSSE with YIG thickness. • The model agrees qualitatively with the measured dependence of LSSE on magnetic field.

Spin drift and spin diffusion currents in semiconductors

Energy Technology Data Exchange (ETDEWEB)

Idrish Miah, M [Nanoscale Science and Technology Centre and School of Biomolecular and Physical Sciences, Griffith University, Nathan, Brisbane, QLD 4111 (Australia)], E-mail: m.miah@griffith.edu.au

2008-09-15

On the basis of a spin drift-diffusion model, we show how the spin current is composed and find that spin drift and spin diffusion contribute additively to the spin current, where the spin diffusion current decreases with electric field while the spin drift current increases, demonstrating that the extension of the spin diffusion length by a strong field does not result in a significant increase in spin current in semiconductors owing to the competing effect of the electric field on diffusion. We also find that there is a spin drift-diffusion crossover field for a process in which the drift and diffusion contribute equally to the spin current, which suggests a possible method of identifying whether the process for a given electric field is in the spin drift or spin diffusion regime. Spin drift-diffusion crossover fields for GaAs are calculated and are found to be quite small. We derive the relations between intrinsic spin diffusion length and the spin drift-diffusion crossover field of a semiconductor for different electron statistical regimes. The findings resulting from this investigation might be important for semiconductor spintronics.

Spin drift and spin diffusion currents in semiconductors

Directory of Open Access Journals (Sweden)

M Idrish Miah

2008-01-01

Full Text Available On the basis of a spin drift-diffusion model, we show how the spin current is composed and find that spin drift and spin diffusion contribute additively to the spin current, where the spin diffusion current decreases with electric field while the spin drift current increases, demonstrating that the extension of the spin diffusion length by a strong field does not result in a significant increase in spin current in semiconductors owing to the competing effect of the electric field on diffusion. We also find that there is a spin drift-diffusion crossover field for a process in which the drift and diffusion contribute equally to the spin current, which suggests a possible method of identifying whether the process for a given electric field is in the spin drift or spin diffusion regime. Spin drift-diffusion crossover fields for GaAs are calculated and are found to be quite small. We derive the relations between intrinsic spin diffusion length and the spin drift-diffusion crossover field of a semiconductor for different electron statistical regimes. The findings resulting from this investigation might be important for semiconductor spintronics.

Spin drift and spin diffusion currents in semiconductors

International Nuclear Information System (INIS)

Idrish Miah, M

2008-01-01

On the basis of a spin drift-diffusion model, we show how the spin current is composed and find that spin drift and spin diffusion contribute additively to the spin current, where the spin diffusion current decreases with electric field while the spin drift current increases, demonstrating that the extension of the spin diffusion length by a strong field does not result in a significant increase in spin current in semiconductors owing to the competing effect of the electric field on diffusion. We also find that there is a spin drift-diffusion crossover field for a process in which the drift and diffusion contribute equally to the spin current, which suggests a possible method of identifying whether the process for a given electric field is in the spin drift or spin diffusion regime. Spin drift-diffusion crossover fields for GaAs are calculated and are found to be quite small. We derive the relations between intrinsic spin diffusion length and the spin drift-diffusion crossover field of a semiconductor for different electron statistical regimes. The findings resulting from this investigation might be important for semiconductor spintronics.

Spin relaxation rates in quantum dots: Role of the phonon modulated spin orbit interaction

Science.gov (United States)

Alcalde, A. M.; Romano, C. L.; Marques, G. E.

2008-11-01

We calculate the spin relaxation rates in InAs and GaAs parabolic quantum dots due to the interaction of spin carriers with acoustical phonons. We consider a spin relaxation mechanism completely intrinsic to the system, since it is based on the modulation of the spin-orbit interaction by the acoustic phonon potential, which is independent of any structural properties of the confinement potential. The electron-phonon deformation potential and the piezoelectric interaction are described by the Pavlov-Firsov spin-phonon Hamiltonian. Our results demonstrate that, for narrow-gap semiconductors, the deformation potential interaction becomes dominant. This behavior is not observed for wide or intermediate gap semiconductors, where the piezoelectric coupling, in general, governs the relaxation processes. We also demonstrate that the spin relaxation rates are particularly sensitive to values of the Landé g-factor, which depend strongly on the spatial shape of the confinement.

Rigorous decoupling between edge states in frustrated spin chains and ladders

Science.gov (United States)

Chepiga, Natalia; Mila, Frédéric

2018-05-01

We investigate the occurrence of exact zero modes in one-dimensional quantum magnets of finite length that possess edge states. Building on conclusions first reached in the context of the spin-1/2 X Y chain in a field and then for the spin-1 J1-J2 Heisenberg model, we show that the development of incommensurate correlations in the bulk invariably leads to oscillations in the sign of the coupling between edge states, and hence to exact zero energy modes at the crossing points where the coupling between the edge states rigorously vanishes. This is true regardless of the origin of the frustration (e.g., next-nearest-neighbor coupling or biquadratic coupling for the spin-1 chain), of the value of the bulk spin (we report on spin-1/2, spin-1, and spin-2 examples), and of the value of the edge-state emergent spin (spin-1/2 or spin-1).

Spin Hall conductance in a Y-shaped junction device in presence of tunable spin-orbit coupling

Science.gov (United States)

Ganguly, Sudin; Basu, Saurabh

2017-06-01

We study spin Hall effect in a three terminal Y-shaped device in presence of tunable spin-orbit (SO) interactions via Landauer-Büttiker formalism. We have evolved a fabrication technique for creating different angular separation between the two arms of the Y-shaped device so as to investigate the effect of angular width on the spin Hall conductance (SHC). A smaller angular separation yields a larger conductance. Also arbitrary orientation of the spin quantization axes yields interesting three dimensional contour maps for the SHC corresponding to different angular separation of the Y-shaped device. In addition to the GSH demonstrating bounded behaviour for different angular separations, there are distinct symmetry axes about which SHC demonstrates reflection symmetry. The results explicitly show breaking of the spin rotational symmetry. Further a systematic study is carried out to compare and contrast between the different SO terms, such as Rashba and Dresselhaus SO interactions and the interplay of the angular separation therein.

Spin correlations in quantum wires

Science.gov (United States)

Sun, Chen; Pokrovsky, Valery L.

2015-04-01

We consider theoretically spin correlations in a one-dimensional quantum wire with Rashba-Dresselhaus spin-orbit interaction (RDI). The correlations of noninteracting electrons display electron spin resonance at a frequency proportional to the RDI coupling. Interacting electrons, upon varying the direction of the external magnetic field, transit from the state of Luttinger liquid (LL) to the spin-density wave (SDW) state. We show that the two-time total-spin correlations of these states are significantly different. In the LL, the projection of total spin to the direction of the RDI-induced field is conserved and the corresponding correlator is equal to zero. The correlators of two components perpendicular to the RDI field display a sharp electron-spin resonance driven by the RDI-induced intrinsic field. In contrast, in the SDW state, the longitudinal projection of spin dominates, whereas the transverse components are suppressed. This prediction indicates a simple way for an experimental diagnostic of the SDW in a quantum wire. We point out that the Luttinger model does not respect the spin conservation since it assumes the infinite Fermi sea. We propose a proper cutoff to correct this failure.

The manifestation of spin-phonon coupling in CaMnO{sub 3}

Energy Technology Data Exchange (ETDEWEB)

Goian, V., E-mail: goian@fzu.cz; Kamba, S.; Borodavka, F.; Nuzhnyy, D.; Savinov, M. [Institute of Physics, The Czech Academy of Sciences, Na Slovance 2, 182 21 Prague (Czech Republic); Belik, A. A. [International Center for Materials Nanoarchitectonics (WPI-MANA), National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba, Ibaraki 305-0044 (Japan)

2015-04-28

Recently predicted presence of spin-phonon coupling in the CaMnO{sub 3} is experimentally confirmed in infrared (IR), Raman and time-domain THz spectra. Most of phonon frequencies seen below 350 cm{sup −1} exhibit significant shifts on cooling below antiferromagnetic phase transition at T{sub N} ≅ 120 K. Moreover, several new modes activate in the IR and Raman spectra on cooling below T{sub N}. Sum of phonon contributions to static permittivity exhibits small but reliable anomaly at T{sub N}. On the other hand, the spin-phonon coupling is not manifested in temperature dependence of radio-frequency permittivity, because intrinsic permittivity is screened by extrinsic contribution from conductivity, which enhances the permittivity to giant values.

Universal Mechanism of Spin Relaxation in Solids

Science.gov (United States)

Chudnovsky, Eugene

2006-03-01

Conventional elastic theory ignores internal local twists and torques. Meantime, spin-lattice relaxation is inherently coupled with local elastic twists through conservation of the total angular momentum (spin + lattice). This coupling gives universal lower bound (free of fitting parameters) on the relaxation of the atomic or molecular spin in a solid [1] and on the relaxation of the electron spin in a quantum dot [2]. [1] E. M. Chudnovsky, D. A. Garanin, and R. Schilling, Phys. Rev. B 72, 094426 (2005). [2] C. Calero, E. M. Chudnovsky, and D. A. Garanin, Phys. Rev. Lett. 95, 166603 (2005).

Generalized theory of spin fluctuations in itinerant electron magnets: Crucial role of spin anharmonicity

International Nuclear Information System (INIS)

Solontsov, A.

2015-01-01

The paper critically overviews the recent developments of the theory of spatially dispersive spin fluctuations (SF) in itinerant electron magnetism with particular emphasis on spin-fluctuation coupling or spin anharmonicity. It is argued that the conventional self-consistent renormalized (SCR) theory of spin fluctuations is usually used aside of the range of its applicability actually defined by the constraint of weak spin anharmonicity based on the random phase approximation (RPA) arguments. An essential step in understanding SF in itinerant magnets beyond RPA-like arguments was made recently within the soft-mode theory of SF accounting for strong spin anharmonicity caused by zero-point SF. In the present paper we generalize it to apply for a wider range of temperatures and regimes of SF and show it to lead to qualitatively new results caused by zero-point effects. - Highlights: • We review the spin-fluctuation theory of itinerant electron magnets with account of zero-point effects. • We generalize the existing theory to account for different regimes of spin fluctuations. • We show that zero-point spin fluctuations play a crucial role in both low- and high-temperature properties of metallic magnets. • We argue that a new scheme of calculation of ground state properties of magnets is needed including zero-point effects

Spin-spin cross-relaxation of optically-excited rare-earth ions in crystals

International Nuclear Information System (INIS)

Otto, F.W.; D'Amato, F.X.; Hahn, E.L.; Lukas, M.

1986-01-01

A laser saturation grating experiment is applied for the measurement of electron hyperfine state spin orientation diffusion among Tm +2 impurity ion hyperfine ground states in SrF 2 . A strong laser pulse at λ 1 produces a spatial grating of excited spin states followed by a probe at λ 2 . The probe transmission intensity is to assess diffusion of non-equilibrium spin population into regions not excited by the pulse at λ 1 . In a second experiment, a field sweep laser hole burning method enables measurement of Pr +3 optical ion hyperfine coupling of optical ground states to the reservoir of F nuclear moments in LaF 3 by level crossing. A related procedure with external RF resonance sweep excitation maps out the nuclear Zeeman-electric quadrupole coupled spectrum of Pr +3 over a wide range by monitoring laser beam transmission absorption

Spin Polarization Oscillations without Spin Precession: Spin-Orbit Entangled Resonances in Quasi-One-Dimensional Spin Transport

Directory of Open Access Journals (Sweden)

D. H. Berman

2014-03-01

Full Text Available Resonant behavior involving spin-orbit entangled states occurs for spin transport along a narrow channel defined in a two-dimensional electron gas, including an apparent rapid relaxation of the spin polarization for special values of the channel width and applied magnetic field (so-called ballistic spin resonance. A fully quantum-mechanical theory for transport using multiple subbands of the one-dimensional system provides the dependence of the spin density on the applied magnetic field and channel width and position along the channel. We show how the spatially nonoscillating part of the spin density vanishes when the Zeeman energy matches the subband energy splittings. The resonance phenomenon persists in the presence of disorder.

Spin-exchange and spin-destruction rates for the 3He-Na system