WorldWideScience

Sample records for field-induced metal-insulator transition

  1. Magnetic-field-induced superconductor-metal-insulator transitions in bismuth metal graphite

    Science.gov (United States)

    Suzuki, Masatsugu; Suzuki, Itsuko S.; Lee, Robert; Walter, Jürgen

    2002-07-01

    Bismuth metal graphite (MG) has a unique layered structure where Bi nanoparticles are encapsulated between adjacent sheets of nanographites. The superconductivity below Tc (=2.48 K) is due to Bi nanoparticles. The Curie-like susceptibility below 30 K is due to conduction electrons localized near zigzag edges of nanographites. A magnetic-field-induced transition from metallic to semiconductorlike phase is observed in the in-plane resistivity ρa around Hc (~25 kOe) for both H⊥c and H||c (c: c axis). A negative magnetoresistance in ρa for H⊥c (040 kOe) suggest the occurrence of a two-dimensional weak-localization effect.

  2. Magnetic-field induced superconductor-metal-insulator transitions in bismuth metal-graphite

    Science.gov (United States)

    Suzuki, Masatsugu; Suzuki, Itsuko S.; Lee, Robert; Walter, Jürgen

    2002-03-01

    Bismuth-metal graphite (MG) has a unique layered structure where Bi nanoparticles are encapsulated in nanographites. The size of nanographite is on the same order as that of Bi nanographite. The observed superconductivity below Tc (= 2.48 K) and the Curie-like Pauli paramagnetic susceptibility below 30 K are related to the high density of states at the Fermi energy arising from edge states of nanographites.^1 A magnetic-field induced transition from metallic to semiconductor-like phase is observed in the in-plane resistivity ρa around Hc (≈ 25 kOe) for both H⊥c and H‖c (c: c axis). The suppression of the metallic phase by H is independent of the directions of H (H‖c and H⊥c) for Bi-MG, suggesting that the spin related effect is significant compared to the orbital effect. The Zeemann energy gSμ_BH at 25 kOe corresponds to a thermal energy k_BTH with TH = 1.7 K, where g = 2 and S = 1/2. The temperature TH is slightly lower than T_c. A negative magnetoresistance in ρa for H⊥c (040 kOe) suggest the occurrence of two-dimensional weak localization effect. ^1K. Wakabayashi, M. Fujita, H. Ajiki, and M. Sigrist, Phys. Rev. 59, 8271 (1999).

  3. Giant positive magnetoresistance and field-induced metal insulator transition in Cr2NiGa

    Science.gov (United States)

    Pramanick, S.; Dutta, P.; Chatterjee, S.; Giri, S.; Majumdar, S.

    2017-01-01

    We report the magneto-transport properties of the newly synthesized Heusler compound Cr2NiGa which crystallizes in a disordered cubic B2 structure belonging to the Pm\\bar{3} m space group. The sample is found to be paramagnetic down to 2 K with metallic characteristics. On application of a magnetic field, a significantly large increase in resistivity is observed which corresponds to magnetoresistance as high as 112% at 150 kOe of field at the lowest temperature. Most remarkably, the sample shows a negative temperature coefficient of resistivity below about 50 K under the application of field  ⩾80 kOe, signifying a field-induced metal to ‘insulating’ transition. The observed magnetoresistance follows Kohler’s rule below 20 K indicating the validity of the semiclassical model of electronic transport in metals with a single relaxation time. A multi-band model for electronic transport, originally proposed for semimetals, is found to be appropriate to describe the magneto-transport behavior of the sample.

  4. Temperature and electric field induced metal-insulator transition in atomic layer deposited VO2 thin films

    Science.gov (United States)

    Tadjer, Marko J.; Wheeler, Virginia D.; Downey, Brian P.; Robinson, Zachary R.; Meyer, David J.; Eddy, Charles R.; Kub, Fritz J.

    2017-10-01

    Amorphous vanadium oxide (VO2) films deposited by atomic layer deposition (ALD) were crystallized with an ex situ anneal at 660-670 °C for 1-2 h under a low oxygen pressure (10-4 to 10-5 Torr). Under these conditions the crystalline VO2 phase was maintained, while formation of the V2O5 phase was suppressed. Electrical transition from the insulator to the metallic phase was observed in the 37-60 °C range, with an ROFF/RON ratio of up to about 750 and ΔTC ≅ 7-10 °C. Lateral electric field applied across two-terminal device structures induced a reversible phase change, with a room temperature transition field of about 25 kV/cm in the VO2 sample processed with the 2 h long O2 anneal. Both the width and slope of the field induced MIT I-V hysteresis were dependent upon the VO2 crystalline quality.

  5. Suppression of metal-insulator transition in VO2 by electric field-induced oxygen vacancy formation

    National Research Council Canada - National Science Library

    Jeong, Jaewoo; Aetukuri, Nagaphani; Graf, Tanja; Schladt, Thomas D; Samant, Mahesh G; Parkin, Stuart S P

    2013-01-01

    .... We found that electrolyte gating of VO(2) leads not to electrostatically induced carriers but instead to the electric field-induced creation of oxygen vacancies, with consequent migration of oxygen from the oxide film into the ionic liquid...

  6. Switchable Metal-Insulator Phase Transition Metamaterials.

    Science.gov (United States)

    Hajisalem, Ghazal; Nezami, Mohammadreza S; Gordon, Reuven

    2017-05-10

    We investigate the switching of a gap plasmon tunnel junction between conducting and insulating states. Hysteresis is observed in the second and the third harmonic generation power dependence, which arises by thermally induced disorder ("melting") of a two-carbon self-assembled monolayer between an ultraflat gold surface and metal nanoparticles. The hysteresis is observed for a variety of nanoparticle sizes, but not for larger tunnel junctions where there is no appreciable tunneling. By combining quantum corrected finite-difference time-domain simulations with nonlinear scattering theory, we calculate the changes in the harmonic generation between the tunneling and the insulating states, and good agreement is found with the experiments. This paves the way to a new class of metal-insulator phase transition switchable metamaterials, which may provide next-generation information processing technologies.

  7. Crossover of angular dependent magnetoresistance with the metal-insulator transition in colossal magnetoresistive manganite films

    DEFF Research Database (Denmark)

    Chen, Yunzhong; Sun, J.R.; Zhao, T.Y.;

    2009-01-01

    directions was observed with the appearance of magnetic-field-induced metal-insulator transition, which further led to a sign crossover in the AMR effect. The AMR crossover may give a direct evidence of the drastic modification of electronic structure or possible orbital reconstruction with the magnetic...

  8. Metal-Insulator Transition in C60-Polymers

    CERN Document Server

    Harigaya, K

    1995-01-01

    Variations in the band structures of C60-polymers are studied, when pi-conjugation conditions are changed. We look at band structures in order to discuss a metal-insulator transition, using a semi-empirical model with the Su-Schrieffer-Heeger type electron-phonon interactions. We find that electronic structures change among direct-gap insulators and the metal, depending on the degree of pi-conjugations. High pressure experiments could observe such pressure-induced metal-insulator transitions.

  9. Disorder- and correlation-driven metal-insulator transitions

    OpenAIRE

    Balzer, Matthias; Potthoff, Michael

    2004-01-01

    Metal-insulator transitions driven by disorder (Delta) and/or by electron correlations (U) are investigated within the Anderson-Hubbard model with local binary-alloy disorder using a simple but consistent mean-field approach. The Delta-U phase diagram is derived and discussed for T=0 and finite temperatures.

  10. Thermal metal-insulator transition in a helical topological superconductor

    OpenAIRE

    Fulga, I. C.; Akhmerov, A. R.; Tworzydło, J.; Béri, B.; Beenakker, C. W. J.

    2012-01-01

    Two-dimensional superconductors with time-reversal symmetry have a Z_2 topological invariant, that distinguishes phases with and without helical Majorana edge states. We study the topological phase transition in a class-DIII network model, and show that it is associated with a metal-insulator transition for the thermal conductance of the helical superconductor. The localization length diverges at the transition with critical exponent nu approx 2.0, about twice the known value in a chiral supe...

  11. Quantum critical transport at a continuous metal-insulator transition

    OpenAIRE

    Haldar, P.; Laad, M. S.; Hassan, S. R.

    2016-01-01

    In contrast to the first-order correlation-driven Mott metal-insulator transition (MIT), contin- uous disorder-driven transitions are intrinsically quantum critical. Here, we investigate transport quantum criticality in the Falicov-Kimball model, a representative of the latter class in the "strong disorder" category. Employing cluster-dynamical mean-field theory (CDMFT), we find clear and anomalous quantum critical scaling behavior manifesting as perfect mirror symmetry of scaling curves on b...

  12. Disorder-Driven Metal-Insulator Transitions in Deformable Lattices

    Science.gov (United States)

    Di Sante, Domenico; Fratini, Simone; Dobrosavljević, Vladimir; Ciuchi, Sergio

    2017-01-01

    We show that, in the presence of a deformable lattice potential, the nature of the disorder-driven metal-insulator transition is fundamentally changed with respect to the noninteracting (Anderson) scenario. For strong disorder, even a modest electron-phonon interaction is found to dramatically renormalize the random potential, opening a mobility gap at the Fermi energy. This process, which reflects disorder-enhanced polaron formation, is here given a microscopic basis by treating the lattice deformations and Anderson localization effects on the same footing. We identify an intermediate "bad insulator" transport regime which displays resistivity values exceeding the Mott-Ioffe-Regel limit and with a negative temperature coefficient, as often observed in strongly disordered metals. Our calculations reveal that this behavior originates from significant temperature-induced rearrangements of electronic states due to enhanced interaction effects close to the disorder-driven metal-insulator transition.

  13. Metal-insulator transition in films of doped semiconductor nanocrystals.

    Science.gov (United States)

    Chen, Ting; Reich, K V; Kramer, Nicolaas J; Fu, Han; Kortshagen, Uwe R; Shklovskii, B I

    2016-03-01

    To fully deploy the potential of semiconductor nanocrystal films as low-cost electronic materials, a better understanding of the amount of dopants required to make their conductivity metallic is needed. In bulk semiconductors, the critical concentration of electrons at the metal-insulator transition is described by the Mott criterion. Here, we theoretically derive the critical concentration nc for films of heavily doped nanocrystals devoid of ligands at their surface and in direct contact with each other. In the accompanying experiments, we investigate the conduction mechanism in films of phosphorus-doped, ligand-free silicon nanocrystals. At the largest electron concentration achieved in our samples, which is half the predicted nc, we find that the localization length of hopping electrons is close to three times the nanocrystals diameter, indicating that the film approaches the metal-insulator transition.

  14. On metal-insulator transition in cubic fullerides

    Science.gov (United States)

    Iwahara, Naoya; Chibotaru, Liviu

    The interplay between degenerate orbital and electron correlation is a key to characterize the electronic phases in, for example, transition metal compounds and alkali-doped fullerides. Besides, the degenerate orbital couples to spin and lattice degrees of freedom ,giving rise to exotic phenomena. Here, we develop the self-consistent Gutzwiller approach for the simultaneous treatment of the Jahn-Teller effect and electron correlation, and apply the methodology to reveal the nature of the ground electronic state of fullerides. For small Coulomb repulsion on site U, the fulleride is quasi degenerate correlated metal. With increase of U, we found the quantum phase transition from the metallic phase to JT split phase. In the latter, the Mott transition (MT) mainly develops in the half-filled subband, whereas the empty and the completely filled subbands are almost uninvolved. Therefore, we can qualify the metal-insulator transition in fullerides as an orbital selective MT induced by JT effect.

  15. Metal-insulator transition: the Mott criterion and coherence length

    CERN Document Server

    Pergament, A

    2003-01-01

    On the basis of the Mott criterion for metal-insulator transition (MIT), an expression for the correlation length, identical to that for the coherence length in the theory of superconductivity, is obtained. This correlation length characterizes the size of an electron-hole pair (in an excitonic insulator) or the effective Bohr radius (as, e.g., in doped semiconductors). The relation obtained is used for calculation of the coherence length in vanadium dioxide. The presence of two characteristic coherence lengths (xi sub 1 approx 20 A and xi sub 2 approx 2 A) is found. This is associated with the specific features of the transition mechanism in VO sub 2 : this mechanism represents a combination of the purely electronic Mott-Hubbard contribution and the structural (Peierls-like) one. It is shown, however, that the driving force of the MIT in VO sub 2 is the electron-correlation Mott-Hubbard transition.

  16. Holographic Metal-Insulator Transition in Higher Derivative Gravity

    CERN Document Server

    Ling, Yi; Wu, Jian-Pin; Zhou, Zhenhua

    2016-01-01

    We introduce a Weyl term into the Einstein-Maxwell-Axion theory in four dimensional spacetime. Up to the first order of the Weyl coupling parameter $\\gamma$, we construct charged black brane solutions without translational invariance in a perturbative manner. Among all the holographic frameworks involving higher derivative gravity, we are the first to obtain metal-insulator transitions (MIT) when varying the system parameters at zero temperature. Furthermore, we study the holographic entanglement entropy (HEE) of strip geometry in this model and find that the second order derivative of HEE with respect to the axion parameter exhibits maximization behavior near quantum critical points (QCPs) of MIT. It testifies the conjecture in 1502.03661 and 1604.04857 that HEE itself or its derivatives can be used to diagnose quantum phase transition (QPT).

  17. Holographic metal-insulator transition in higher derivative gravity

    Directory of Open Access Journals (Sweden)

    Yi Ling

    2017-03-01

    Full Text Available We introduce a Weyl term into the Einstein–Maxwell-Axion theory in four dimensional spacetime. Up to the first order of the Weyl coupling parameter γ, we construct charged black brane solutions without translational invariance in a perturbative manner. Among all the holographic frameworks involving higher derivative gravity, we are the first to obtain metal-insulator transitions (MIT when varying the system parameters at zero temperature. Furthermore, we study the holographic entanglement entropy (HEE of strip geometry in this model and find that the second order derivative of HEE with respect to the axion parameter exhibits maximization behavior near quantum critical points (QCPs of MIT. It testifies the conjecture in [1,2] that HEE itself or its derivatives can be used to diagnose quantum phase transition (QPT.

  18. Holographic metal-insulator transition in higher derivative gravity

    Science.gov (United States)

    Ling, Yi; Liu, Peng; Wu, Jian-Pin; Zhou, Zhenhua

    2017-03-01

    We introduce a Weyl term into the Einstein-Maxwell-Axion theory in four dimensional spacetime. Up to the first order of the Weyl coupling parameter γ, we construct charged black brane solutions without translational invariance in a perturbative manner. Among all the holographic frameworks involving higher derivative gravity, we are the first to obtain metal-insulator transitions (MIT) when varying the system parameters at zero temperature. Furthermore, we study the holographic entanglement entropy (HEE) of strip geometry in this model and find that the second order derivative of HEE with respect to the axion parameter exhibits maximization behavior near quantum critical points (QCPs) of MIT. It testifies the conjecture in [1,2] that HEE itself or its derivatives can be used to diagnose quantum phase transition (QPT).

  19. Quantum critical transport at a continuous metal-insulator transition

    Science.gov (United States)

    Haldar, P.; Laad, M. S.; Hassan, S. R.

    2016-08-01

    In contrast to the first-order correlation-driven Mott metal-insulator transition, continuous disorder-driven transitions are intrinsically quantum critical. Here, we investigate transport quantum criticality in the Falicov-Kimball model, a representative of the latter class in the strong disorder category. Employing cluster-dynamical mean-field theory, we find clear and anomalous quantum critical scaling behavior manifesting as perfect mirror symmetry of scaling curves on both sides of the MIT. Surprisingly, we find that the beta function β (g ) scales as log(g ) deep into the bad-metallic phase as well, providing a sound unified basis for these findings. We argue that such strong localization quantum criticality may manifest in real three-dimensional systems where disorder effects are more important than electron-electron interactions.

  20. On holographic disorder-driven metal-insulator transitions

    CERN Document Server

    Baggioli, Matteo

    2016-01-01

    We give a minimal holographic model of a disorder-driven metal-insulator transition. It consists in a CFT with a charge sector and a translation-breaking sector that interact in the most generic way allowed by the symmetries and by dynamical consistency. In the gravity dual, it reduces to a Massive Gravity-Maxwell model with new direct couplings between the Maxwell and metric that are allowed when gravity is massive. We show that, generically, the effect of disorder is to decrease the DC electrical conductivity. This happens to such an extent that the conductivity does not obey any lower bound and can be very small in the insulating phase. In some cases, the large disorder limit produces gradient instabilities that hint at the formation of modulated phases.

  1. Thermal transport across a continuous metal-insulator transition

    Science.gov (United States)

    Haldar, P.; Laad, M. S.; Hassan, S. R.

    2017-09-01

    The celebrated Wiedemann-Franz (WF) law is believed to be robust in metals as long as interactions between electrons preserve their fermion-quasiparticle character. We study thermal transport and the fate of the WF law close to a continuous metal-insulator transition (MIT) in the Falicov-Kimball model (FKM) using cluster-dynamical mean-field theory (CDMFT). Surprisingly, as for electrical transport, we find robust and novel quantum critical scaling in thermal transport across the MIT. We unearth the deeper reasons for these novel findings in terms of (i) the specific structure of energy-current correlations for the FKM and (ii) the microscopic electronic processes which facilitate energy transport while simultaneously blocking charge transport close to the MIT. However, within (C)DMFT, we also find that the WF law survives at T ⟶0 in the incoherent metal right up to the MIT, even in absence of Landau quasiparticles.

  2. Metal-insulator transition in oriented poly(p-phenylenevinylene)

    Science.gov (United States)

    Ahlskog, M.; Menon, Reghu; Heeger, A. J.; Noguchi, T.; Ohnishi, T.

    1997-03-01

    The transport properties of H2 SO4 -doped, tensile drawn, and oriented poly(phenylenevinylene) have been studied in the metallic, critical, and insulating regimes of the disorder-induced metal-insulator transition (M-I) transition. The temperature dependence of the conductivity, σ(T) and the magnetoconductance (MC) were investigated between room temperature and 1.3 K and in magnetic fields up to 8 T, in freshly doped samples and in samples during controlled dedoping (aging). A complete set of measurements were carried out on a single, fully doped sample that was followed during ageing from the metallic state through the critical regime into the insulting state. The transport properties are characterized as a function of the resistivity ratio (ρr), where ρr=[ρ(1.3 K)/ρ(200 K)]. In the metallic regime (ρr50), ρ(T)~exp(T0/T)x indicating variable-range-hopping transport. Although anisotropic, the field and temperature dependences of the transport are similar both parallel and perpendicular to the chain axis, implying that oriented conducting polymers are anisotropic three-dimensional conductors.

  3. Metal-insulator and charge ordering transitions in oxide nanostructures

    Science.gov (United States)

    Singh, Sujay Kumar

    Strongly correlated oxides are a class of materials wherein interplay of various degrees of freedom results in novel electronic and magnetic phenomena. Vanadium oxides are widely studied correlated materials that exhibit metal-insulator transitions (MIT) in a wide temperature range from 70 K to 380 K. In this Thesis, results from electrical transport measurements on vanadium dioxide (VO2) and vanadium oxide bronze (MxV 2O5) (where M: alkali, alkaline earth, and transition metal cations) are presented and discussed. Although the MIT in VO2 has been studied for more than 50 years, the microscopic origin of the transition is still debated since a slew of external parameters such as light, voltage, and strain are found to significantly alter the transition. Furthermore, recent works on electrically driven switching in VO2 have shown that the role of Joule heating to be a major cause as opposed to electric field. We explore the mechanisms behind the electrically driven switching in single crystalline nanobeams of VO2 through DC and AC transport measurements. The harmonic analysis of the AC measurement data shows that non-uniform Joule heating causes electronic inhomogeneities to develop within the nanobeam and is responsible for driving the transition in VO2. Surprisingly, field assisted emission mechanisms such as Poole-Frenkel effect is found to be absent and the role of percolation is also identified in the electrically driven transition. This Thesis also provides a new insight into the mechanisms behind the electrolyte gating induced resistance modulation and the suppression of MIT in VO2. We show that the metallic phase of VO2 induced by electrolyte gating is due to an electrochemical process and can be both reversible and irreversible under different conditions. The kinetics of the redox processes increase with temperature; a complete suppression of the transition and the stabilization of the metallic phase are achievable by gating in the rutile metallic phase

  4. Percolation metal-insullator transition in BiSrCaCuO films

    Science.gov (United States)

    Okunev, V. D.; Pafomov, N. N.; Svistunov, V. M.; Lewandowski, S. J.; Gierlowski, P.; Kula, W.

    1996-02-01

    An experimental investigation of the metal-insulator trnasition in BiSrCaCuO (BSCCO) films is reported. We performed resistivity, optical-absorption and critical-temperature measurements on several samples obtained by different technological methods. The results agree well with the percolation mechanism of the metal-insulator transition and show interesting correlations between room-temperature conductivity and superconducting properties of the investigated films.

  5. Metal-insulator transition and local moment formation: A spin-density functional approach

    Science.gov (United States)

    Ghazali, A.; Leroux-Hugon, P.

    1980-01-01

    A more thorough description of the metal-insulator transition in correlated systems including local moment formation may be achieved through the spin-density functional method when compared to the Hubbard model. We have applied this method to doped semiconductors and found a transition between an insulating phase with local moments and a metallic one without moments.

  6. Terahertz transport dynamics in the metal-insulator transition of V2O3 thin film

    Science.gov (United States)

    Luo, Y. Y.; Su, F. H.; Zhang, C.; Zhong, L.; Pan, S. S.; Xu, S. C.; Wang, H.; Dai, J. M.; Li, G. H.

    2017-03-01

    The dynamic behavior of thermally-induced metal-insulator transition of V2O3 thin film on Si substrate grown by reactive magnetron sputtering was investigated by the terahertz time-domain spectroscopy. It was found that the THz absorption and optical conductivity of the thin films are temperature-dependent, and the THz amplitude modulation can reach as high as 74.7%. The complex THz optical conductivity in the metallic state of the V2O3 thin films can be well-fitted by the Drude-Smith model, which offer the insight into the electron transport dynamic during the metal-insulator transition of the thin film.

  7. Metal-insulator transition of fermions on a kagome lattice at 1/3 filling.

    Science.gov (United States)

    Nishimoto, Satoshi; Nakamura, Masaaki; O'Brien, Aroon; Fulde, Peter

    2010-05-14

    We discuss the metal-insulator transition of the spinless fermion model on a kagome lattice at 1/3 filling. The system is analyzed by using exact diagonalization, density-matrix renormalization group methods, and random-phase approximation. In the strong-coupling region, the charge-ordered ground state is consistent with the predictions of an effective model, i.e., plaquette order. We find that the qualitative properties of the metal-insulator transition are totally different depending on the sign of the hopping matrix elements, reflecting the difference in the band structure near the Fermi level.

  8. Control of metal-insulator transition in (EDO-TTF)2SbF6

    Science.gov (United States)

    Maesato, Mitsuhiko; Nakano, Yoshiaki; Shao, Xiangfeng; Yoshida, Yukihiro; Yamochi, Hideki; Saito, Gunzi; Moreac, Alain; Ameline, Jean-Claude; Collet, Eric; Uruichi, Mikio; Yakushi, Kyuya

    2009-02-01

    We have examined the temperature dependence of optical reflectance spectra of (EDO-TTF)2SbF6 salt, and succeeded to detect the thermal hysteresis by the reflectance spectra. In order to investigate high pressure effects on the metal-insulator transition of SbF6 salt, we have performed Raman experiments under pressures up to 6 kbar. Drastic changes in the frequencies of charge sensitive C=C stretching modes suggested the pressure-induced reentrant metal-insulator-metal transition at room temperature.

  9. Universal Quantum Criticality in the Metal-Insulator Transition of Two-Dimensional Interacting Dirac Electrons

    Science.gov (United States)

    Otsuka, Yuichi; Yunoki, Seiji; Sorella, Sandro

    2016-01-01

    The metal-insulator transition has been a subject of intense research since Mott first proposed that the metallic behavior of interacting electrons could turn to an insulating one as electron correlations increase. Here, we consider electrons with massless Dirac-like dispersion in two spatial dimensions, described by the Hubbard models on two geometrically different lattices, and perform numerically exact calculations on unprecedentedly large systems that, combined with a careful finite-size scaling analysis, allow us to explore the quantum critical behavior in the vicinity of the interaction-driven metal-insulator transition. Thereby, we find that the transition is continuous, and we determine the quantum criticality for the corresponding universality class, which is described in the continuous limit by the Gross-Neveu model, a model extensively studied in quantum field theory. Furthermore, we discuss a fluctuation-driven scenario for the metal-insulator transition in the interacting Dirac electrons: The metal-insulator transition is triggered only by the vanishing of the quasiparticle weight, not by the Dirac Fermi velocity, which instead remains finite near the transition. This important feature cannot be captured by a simple mean-field or Gutzwiller-type approximate picture but is rather consistent with the low-energy behavior of the Gross-Neveu model.

  10. Universal Quantum Criticality in the Metal-Insulator Transition of Two-Dimensional Interacting Dirac Electrons

    Directory of Open Access Journals (Sweden)

    Yuichi Otsuka

    2016-03-01

    Full Text Available The metal-insulator transition has been a subject of intense research since Mott first proposed that the metallic behavior of interacting electrons could turn to an insulating one as electron correlations increase. Here, we consider electrons with massless Dirac-like dispersion in two spatial dimensions, described by the Hubbard models on two geometrically different lattices, and perform numerically exact calculations on unprecedentedly large systems that, combined with a careful finite-size scaling analysis, allow us to explore the quantum critical behavior in the vicinity of the interaction-driven metal-insulator transition. Thereby, we find that the transition is continuous, and we determine the quantum criticality for the corresponding universality class, which is described in the continuous limit by the Gross-Neveu model, a model extensively studied in quantum field theory. Furthermore, we discuss a fluctuation-driven scenario for the metal-insulator transition in the interacting Dirac electrons: The metal-insulator transition is triggered only by the vanishing of the quasiparticle weight, not by the Dirac Fermi velocity, which instead remains finite near the transition. This important feature cannot be captured by a simple mean-field or Gutzwiller-type approximate picture but is rather consistent with the low-energy behavior of the Gross-Neveu model.

  11. Reflection symmetry at a B=0 metal-insulator transition in two dimensions

    OpenAIRE

    Simonian, D.; Kravchenko, S. V.; Sarachik, M. P.

    1996-01-01

    We report a remarkable symmetry between the resistivity and conductivity on opposite sides of the B=0 metal-insulator transition in a two-dimensional electron gas in high-mobility silicon MOSFET's. This symmetry implies that the transport mechanisms on the two sides are related.

  12. Metal insulator transition and Froehlich conductivity in the Su-Schrieffer-Heeger model

    NARCIS (Netherlands)

    Michielsen, Kristel; Raedt, Hans De

    1996-01-01

    A quantum molecular dynamics technique is used to study the single-particle density of states, Drude weight, optical conductivity and flux quantization in the Su-Schrieffer-Heeger (SSH) model. Our simulation data show that the SSH model has a metal-insulator transition away from half-filling. In the

  13. Metal-insulator transition and Frohlich conductivity in the Su-Schrieffer-Heeger model

    NARCIS (Netherlands)

    Michielsen, K.F L; de Raedt, H.A.

    1996-01-01

    A quantum molecular dynamics technique is used to study the single-particle density of states, Drude weight, optical conductivity and flux quantization in the Su-Schrieffer-Heeger (SSH) model. Our simulation data show that the SSH model has a metal-insulator transition away from half-filling. In the

  14. Disorder-driven metal-insulator transitions from dirty black holes

    CERN Document Server

    Fadafan, Kazem Bitaghsir

    2016-01-01

    In this paper we study disorder-driven metal-insulator transition in the holographic disordered Einstein-Maxwell-dilaton theories. We study analytically the DC conductivity of such holographic models in terms of black hole horizon data. As it is expected, the electrical conductivity does not obey the lower bound.

  15. Dynamically tracking the joule heating effect on the voltage induced metal-insulator transition in VO2 crystal film

    Directory of Open Access Journals (Sweden)

    G. M. Liao

    2016-04-01

    Full Text Available Insulator to metal phase transitions driven by external electric field are one of the hottest topics in correlated oxide study. While this electric triggered phenomena always mixes the electric field switching effect and joule thermal effect together, which are difficult to clarify the intrinsic mechanism. In this paper, we investigate the dynamical process of voltage-triggered metal-insulator transition (MIT in a VO2 crystal film and observe the temperature dependence of the threshold voltages and switching delay times, which can be explained quite well based on a straightforward joule thermal model. By conducting the voltage controlled infrared transmittance measurement, the delayed infrared transmission change is also observed, further confirming the homogeneous switching process for a large-size film. All of these results show strong evidences that joule thermal effect plays a dominated role in electric-field-induced switching of VO2 crystal.

  16. Dynamically tracking the joule heating effect on the voltage induced metal-insulator transition in VO2 crystal film

    Science.gov (United States)

    Liao, G. M.; Chen, S.; Fan, L. L.; Chen, Y. L.; Wang, X. Q.; Ren, H.; Zhang, Z. M.; Zou, C. W.

    2016-04-01

    Insulator to metal phase transitions driven by external electric field are one of the hottest topics in correlated oxide study. While this electric triggered phenomena always mixes the electric field switching effect and joule thermal effect together, which are difficult to clarify the intrinsic mechanism. In this paper, we investigate the dynamical process of voltage-triggered metal-insulator transition (MIT) in a VO2 crystal film and observe the temperature dependence of the threshold voltages and switching delay times, which can be explained quite well based on a straightforward joule thermal model. By conducting the voltage controlled infrared transmittance measurement, the delayed infrared transmission change is also observed, further confirming the homogeneous switching process for a large-size film. All of these results show strong evidences that joule thermal effect plays a dominated role in electric-field-induced switching of VO2 crystal.

  17. Effect of the metal-insulator transition on the spin-glass interaction

    Science.gov (United States)

    Hauser, J. J.; Felder, R. J.; Blitzer, L. D.

    1986-03-01

    The effect of the metal-insulator transition on the spin-glass interaction was studied by measuring the magnetic properties of (MnSi)O X as a function of oxygen content X. As X varies from 0 to 3.6 one changes from a metallic to an insulating spin-glass. The transition at X ≲ 1 is marked by a sharp decrease in the susceptibility and a change of the Curie-Weiss temperature (θ) from ferromagnetic to antiferromagnetic.

  18. Oxygen vacancy induced metal-insulator transition in LaNiO3

    Science.gov (United States)

    Misra, Debolina; Kundu, Tarun Kumar

    2016-01-01

    First principle calculations were carried out to examine the metal-insulator transition in LaNiO3 due to changes in oxygen content and consequent alteration of valence state of nickel. The optical properties of all the oxygen deficient LaNiO3-x compounds were calculated to illustrate the electronic structures of the compounds and the change they undergo during the metal-insulator transition. The metallic nature of LaNiO3 is characterized by the Drude peak in the optical conductivity spectra and the high reflectivity it exhibits in the low frequency region. The complex dielectric function and the optical conductivity spectra clearly show that, for x = 0.25, i.e., LaNiO2.75 becomes a semiconductor. As x increases further to 0.5, a gap in the optical spectra appears, indicating the insulating nature of LaNiO2.5. The insulating state of LaNiO2.5 is best described by the GW+HSE method which gives a good estimation of the optical gap of the material. The absorption spectra of LaNiO2.5 clearly reveal that this material is transparent in the low frequency region. This metal-insulator transition is followed by another insulator to semiconductor transition, as x is increased further to 1 i.e., in case of LaNiO2. The metal-insulator transition is then explained on the basis of electron localization function calculations, which show the increase in the covalent bonding in the system as the transition to the insulating state sets in.

  19. Metal-insulator transition and superconductivity in heavily boron-doped diamond and related materials

    Energy Technology Data Exchange (ETDEWEB)

    Achatz, Philipp

    2009-05-15

    During this PhD project, the metal-insulator transition and superconductivity of highly boron-doped single crystal diamond and related materials have been investigated. The critical boron concentration n{sub c} for the metal-insulator transition was found to be the same as for the normal-superconductor transition. All metallic samples have been found to be superconducting and we were able to link the occurence of superconductivity to the proximity to the metal-insulator transition. For this purpose, a scaling law approach based on low temperature transport was proposed. Furthermore, we tried to study the nature of the superconductivity in highly boron doped single crystal diamond. Raman spectroscopy measurements on the isotopically substituted series suggest that the feature occuring at low wavenumbers ({approx} 500 cm{sup -1}) is the A1g vibrational mode associated with boron dimers. Usual Hall effect measurements yielded a puzzling situation in metallic boron-doped diamond samples, leading to carrier concentrations up to a factor 10 higher than the boron concentration determined by secondary ion mass spectroscopy (SIMS). The low temperature transport follows the one expected for a granular metal or insulator, depending on the interplay of intergranular and intragranular (tunneling) conductance. The metal-insulator transition takes place at a critical conductance g{sub c}. The granularity also influences significantly the superconducting properties by introducing the superconducting gap {delta} in the grain and Josephson coupling J between superconducting grains. A peak in magnetoresistance is observed which can be explained by superconducting fluctuations and the granularity of the system. Additionally we studied the low temperature transport of boron-doped Si samples grown by gas immersion laser doping, some of which yielded a superconducting transition at very low temperatures. Furthermore, preliminary results on the LO-phonon-plasmon coupling are shown for the

  20. Non-Achievability of Metal-Insulator Transition in Two-Dimensional Systems

    Institute of Scientific and Technical Information of China (English)

    A. John Peter

    2006-01-01

    @@ We present a simple demonstration of the non feasibility of metal-insulator transition in an exactly two-dimensional (2D) system. The Hartree-Fock potential in the 3D system is suitably modified and presented for the 2D case.The many body effects are included in the screening function, and binding energies of a donor are obtained as a function of impurity concentration so as to find out the possible way leading metal-insulator transition in the 2D system. While solving for the binding energy for a shallow donor in an isolated well of a GaAs/Ga1-x Als As superlattice system within the effective mass approximation, it leads to unphysical results for higher concentrations.

  1. Metal-insulator transition in Na{sub x}WO{sub 3}: Photoemission spectromicroscopy study

    Energy Technology Data Exchange (ETDEWEB)

    Paul, Sanhita, E-mail: raj@iiserkol.ac.in; Ghosh, Anirudha, E-mail: raj@iiserkol.ac.in; Raj, Satyabrata, E-mail: raj@iiserkol.ac.in [Department of Physical Sciences, Indian Institute of Science Education and Research - Kolkata, Mohanpur Campus, Nadia -741252, West Bengal (India)

    2014-04-24

    We have investigated the validity of percolation model, which is quite often invoked to explain the metal-insulator transition in sodium tungsten bronzes, Na{sub x}WO{sub 3} by photoelectron spectromicroscopy. The spatially resolved direct spectromicroscopic probing on both the insulating and metallic phases of high quality single crystals of Na{sub x}WO{sub 3} reveals the absence of any microscopic inhomogeneities embedded in the system within the experimental limit. Neither any metallic domains in the insulating host nor any insulating domains in the metallic host have been found to support the validity of percolation model to explain the metal-insulator transition in Na{sub x}WO{sub 3}.

  2. Disorder and metal-insulator transitions in Weyl semimetals

    Science.gov (United States)

    Jiang, Hua; Chen, Chui-Zhen; Song, Juntao; Sun, Qing-Feng; Wang, Ziqiang; Xie, X. C.

    The Weyl semimetal (WSM) is a newly proposed quantum state of matter. It has Weyl nodes in bulk excitations and Fermi arcs surface states. We study the effects of disorder and localization in WSMs and find three novel phase transitions.(I) Two Weyl nodes near the Brillouin zone boundary can be annihilated pairwise by disorder scattering, resulting in the opening of a topologically nontrivial gap and a transition from a WSM to a three-dimensional (3D) quantum anomalous Hall state. (II) When the two Weyl nodes are well separated in momentum space, the emergent bulk extended states can give rise to a direct transition from a WSM to a 3D diffusive anomalous Hall metal. (III) Two Weyl nodes can emerge near the zone center when an insulating gap closes with increasing disorder, enabling a direct transition from a normal band insulator to a WSM. We determine the phase diagram by numerically computing the localization length and the Hall conductivity, and propose that the novel phase transitions can be realized on a photonic lattice.

  3. Metal-Insulator Transition of Solid Hydrogen by the Antisymmetric Shadow Wave Function

    CERN Document Server

    Calcavecchia, Francesco

    2016-01-01

    We present an improved shadow wave function approach to quantum Monte Carlo for large-scale fermionic systems. It is based on employing the antisymmetric shadow wave function in conjunction with the Gaussian determinant method to reduce the variance and an enhanced stochastic reconfiguration scheme to efficiently optimize the trail wave function, as well as refined twist averaged boundary conditions and periodic coordinates techniques. The predictive power of this approach is demonstrated by revisiting the pressure-induced metal-insulator-transition of solid hydrogen. It is found that the ameliorated accuracy of the antisymmetric shadow wave function results in a significantly increased transition pressure.

  4. Electron spectroscopic investigation of metal-insulator transition in Ce1-SrTiO3

    Indian Academy of Sciences (India)

    U Manju; S R Krishnakumar; Sugata Ray; S Raj; M Onoda; C Carbone; D D Sarma

    2003-10-01

    We have carried out detailed electron spectroscopic investigation of Ce1-SrTiO3 exhibiting insulator-metal transition with . Core level X-ray photoelectron spectra of Ce 3 as well as resonant photoemission spectra obtained at the Ce 4 → 4 resonant absorption threshold establish Ce as being in the trivalent state throughout the series. Using the `off-resonance’ condition for Ce 4 states, we obtain the Ti 3 dominated spectral features close to , exhibiting clear signatures of coherent and incoherent peaks. We discuss the implications of our findings in relation to the metal-insulator transition observed in this series of compounds.

  5. Metal-insulator transition in epitaxial NdNiO3 thin film: A structural, electrical and optical study

    Science.gov (United States)

    Shao, Tao; Qi, Zeming; Wang, Yuyin; Li, Yuanyuan; Yang, Mei; Hu, Chuansheng

    2017-03-01

    NdNiO3 thin film has been prepared by pulsed laser deposition on LaAlO3 (001) single crystalline substrate. Temperature-dependent resistivity measurement shows a sharp metal-insulator transition in such thin film. The phase transition temperature can be tuned from 90 K to 121 K by changing the thickness of thin film. The structure evolution during phase transition is studied by Raman spectroscopy. Optical conductivity reveals that the variation carrier density in the process of phase transition. The results of structural, electrical and optical studies provide useful insights to understand the mechanism of metal-insulator transition of NdNiO3 thin film.

  6. Metal-insulator transition in one-dimensional lattices with chaotic energy sequences

    Energy Technology Data Exchange (ETDEWEB)

    Pinto, R.A. [Laboratorio de Fisica Estadistica, Centro de Fisica, Instituto Venezolano de Investigaciones Cientificas, Apartado 21827, Caracas 1020-A (Venezuela)]. E-mail: ripinto@ivic.ve; Rodriguez, M. [Laboratorio de Fisica Estadistica, Centro de Fisica, Instituto Venezolano de Investigaciones Cientificas, Apartado 21827, Caracas 1020-A (Venezuela); Gonzalez, J.A. [Laboratorio de Fisica Computacional, Centro de Fisica, Instituto Venezolano de Investigaciones Cientificas, Apartado 21827, Caracas 1020-A (Venezuela); Medina, E. [Laboratorio de Fisica Estadistica, Centro de Fisica, Instituto Venezolano de Investigaciones Cientificas, Apartado 21827, Caracas 1020-A (Venezuela)

    2005-06-20

    We study electronic transport through a one-dimensional array of sites by using a tight binding Hamiltonian, whose site-energies are drawn from a chaotic sequence. The correlation degree between these energies is controlled by a parameter regulating the dynamic Lyapunov exponent measuring the degree of chaos. We observe the effect of chaotic sequences on the localization length, conductance, conductance distribution and wave function, finding evidence of a metal-insulator transition (MIT) at a critical degree of chaos. The one-dimensional metallic phase is characterized by a Gaussian conductance distribution and exhibits a peculiar non-selfaveraging.

  7. Multilevel radiative thermal memory realized by the hysteretic metal-insulator transition of vanadium dioxide

    Energy Technology Data Exchange (ETDEWEB)

    Ito, Kota, E-mail: kotaito@mosk.tytlabs.co.jp; Nishikawa, Kazutaka; Iizuka, Hideo [Toyota Central Research and Development Labs, Nagakute, Aichi 480-1192 (Japan)

    2016-02-01

    Thermal information processing is attracting much interest as an analog of electronic computing. We experimentally demonstrated a radiative thermal memory utilizing a phase change material. The hysteretic metal-insulator transition of vanadium dioxide (VO{sub 2}) allows us to obtain a multilevel memory. We developed a Preisach model to explain the hysteretic radiative heat transfer between a VO{sub 2} film and a fused quartz substrate. The transient response of our memory predicted by the Preisach model agrees well with the measured response. Our multilevel thermal memory paves the way for thermal information processing as well as contactless thermal management.

  8. Metal-Insulator Transition in the Hubbard Model: Correlations and Spiral Magnetic Structures

    Science.gov (United States)

    Timirgazin, Marat A.; Igoshev, Petr A.; Arzhnikov, Anatoly K.; Irkhin, Valentin Yu.

    2016-12-01

    The metal-insulator transition (MIT) for the square, simple cubic, and body-centered cubic lattices is investigated within the t-t^' Hubbard model at half-filling by using both the generalized for the case of spiral order Hartree-Fock approximation (HFA) and Kotliar-Ruckenstein slave-boson approach. It turns out that the magnetic scenario of MIT becomes superior over the non-magnetic one. The electron correlations lead to some suppression of the spiral phases in comparison with HFA. We found the presence of a metallic antiferromagnetic (spiral) phase in the case of three-dimensional lattices.

  9. Scaling at the Mott-Hubbard metal-insulator transition in yttrium hydride

    CERN Document Server

    Hoekstra, A F T; Rosenbaum, T F

    2003-01-01

    A single yttrium hydride thin film is conveniently driven through the T 0 metal-insulator transition by fine-tuning the charge carrier density n via persistent photoconductivity at low temperature. Simultaneously, electrical conductivity and Hall measurements are performed for temperatures T down to 350 mK and magnetic fields up to 14 T. A scaling analysis is applied and critical exponents, resolved separately on the metallic and insulating sides of the critical region, are determined consistently. We introduce corrections to scaling to invoke collapse of the data onto a single master curve over an extended region of the (n, T) phase diagram.

  10. Interplay between Ferroelastic and Metal-Insulator Phase Transitions in Strained Quasi-2D VO[subscript 2] Nanoplatelets

    Energy Technology Data Exchange (ETDEWEB)

    Tselev, Alexander; Strelcov, Evgheni; Luk’yanchuk, Igor A.; Budai, John D.; Tischler, Jonathan Z.; Ivanov, Ilia N.; Jones, Keith; Proksch, Roger; Kalinin, Sergei V.; Kolmakov, Aandrei (Asylum); (ORNL); (SIUC); (UPJV)

    2010-07-06

    Formation of ferroelastic twin domains in vanadium dioxide (VO{sub 2}) nanosystems can strongly affect local strain distributions, and hence couple to the strain-controlled metal-insulator transition. Here we report polarized-light optical and scanning microwave microscopy studies of interrelated ferroelastic and metal-insulator transitions in single-crystalline VO{sub 2} quasi-two-dimensional (quasi-2D) nanoplatelets (NPls). In contrast to quasi-1D single-crystalline nanobeams, the 2D geometric frustration results in emergence of several possible families of ferroelastic domains in NPls, thus allowing systematic studies of strain-controlled transitions in the presence of geometrical frustration. We demonstrate the possibility of controlling the ferroelastic domain population by the strength of the NPl-substrate interaction, mechanical stress, and by the NPl lateral size. Ferroelastic domain species and domain walls are identified based on standard group-theoretical considerations. Using variable temperature microscopy, we imaged the development of domains of metallic and semiconducting phases during the metal-insulator phase transition and nontrivial strain-driven reentrant domain formation. A long-range reconstruction of ferroelastic structures accommodating metal-insulator domain formation has been observed. These studies illustrate that a complete picture of the phase transitions in single-crystalline and disordered VO{sub 2} structures can be drawn only if both ferroelastic and metal-insulator strain effects are taken into consideration and understood.

  11. Interplay between Ferroelastic and Metal-Insulator Phase Transitions in Strained Quasi-2D VO[subscript 2] Nanoplatelets

    Energy Technology Data Exchange (ETDEWEB)

    Tselev, Alexander; Strelcov, Evgheni; Luk’yanchuk, Igor A.; Budai, John D.; Tischler, Jonathan Z.; Ivanov, Ilia N.; Jones, Keith; Proksch, Roger; Kalinin, Sergei V.; Kolmakov, Andrei (Asylum); (ORNL); (SIUC); (UPJV)

    2011-08-09

    Formation of ferroelastic twin domains in vanadium dioxide (VO{sub 2}) nanosystems can strongly affect local strain distributions, and hence couple to the strain-controlled metal-insulator transition. Here we report polarized-light optical and scanning microwave microscopy studies of interrelated ferroelastic and metal-insulator transitions in single-crystalline VO{sub 2} quasi-two-dimensional (quasi-2D) nanoplatelets (NPls). In contrast to quasi-1D single-crystalline nanobeams, the 2D geometric frustration results in emergence of several possible families of ferroelastic domains in NPls, thus allowing systematic studies of strain-controlled transitions in the presence of geometrical frustration. We demonstrate the possibility of controlling the ferroelastic domain population by the strength of the NPl-substrate interaction, mechanical stress, and by the NPl lateral size. Ferroelastic domain species and domain walls are identified based on standard group-theoretical considerations. Using variable temperature microscopy, we imaged the development of domains of metallic and semiconducting phases during the metal-insulator phase transition and nontrivial strain-driven reentrant domain formation. A long-range reconstruction of ferroelastic structures accommodating metal-insulator domain formation has been observed. These studies illustrate that a complete picture of the phase transitions in single-crystalline and disordered VO{sub 2} structures can be drawn only if both ferroelastic and metal-insulator strain effects are taken into consideration and understood.

  12. Thermal Conductivity and Thermopower near the 2D Metal-Insulator transition, Final Technical Report

    Energy Technology Data Exchange (ETDEWEB)

    Sarachik, Myriam P. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)

    2015-02-20

    STUDIES OF STRONGLY-INTERACTING 2D ELECTRON SYSTEMS – There is a great deal of current interest in the properties of systems in which the interaction between electrons (their potential energy) is large compared to their kinetic energy. We have investigated an apparent, unexpected metal-insulator transition inferred from the behavior of the temperature-dependence of the resistivity; moreover, detailed analysis of the behavior of the magnetoresistance suggests that the electrons’ effective mass diverges, supporting this scenario. Whether this is a true phase transition or crossover behavior has been strenuously debated over the past 20 years. Our measurements have now shown that the thermoelectric power of these 2D materials diverges at a finite density, providing clear evidence that this is, in fact, a phase transition to a new low-density phase which may be a precursor or a direct transition to the long sought-after electronic crystal predicted by Eugene Wigner in 1934.

  13. Mesoscopic Metal-Insulator Transition at Ferroelastic Domain Walls in VO2

    Energy Technology Data Exchange (ETDEWEB)

    Jones, Keith M [ORNL; Kalinin, Sergei V [ORNL; Kolmakov, Andrei [ORNL; Luk' yanchuk, Prof. Igor A. [University of Picardie Jules Verne, Amiens, France; Meunier, Vincent [ORNL; Proksch, Roger [Asylum Research, Santa Barbara, CA; Shelton Jr, William Allison [ORNL; Strelcov, Evgheni [Southern Illinois University; Tselev, Alexander [ORNL

    2010-01-01

    The novel phenomena induced by symmetry breaking at homointerfaces between ferroic variants in ferroelectric and ferroelastic materials have attracted recently much attention. Using variable temperature scanning microwave microscopy, we demonstrate the mesoscopic strain-induced metal-insulator phase transitions in the vicinity of ferroelastic domain walls in the semiconductive VO2 that nucleated at temperatures as much as 10-12 C below bulk transition, resulting in the formation of conductive channels in the material. Density functional theory is used to rationalize the process low activation energy. This behavior, linked to the strain inhomogeneity inherent in ferroelastic materials, can strongly affect interpretation of phase-transition studies in VO2 and similar materials with symmetry-lowering transitions, and can also be used to enable new generations of electronic devices though strain engineering of conductive and semiconductive regions.

  14. Striped nanoscale phase separation at the metal-insulator transition of heteroepitaxial nickelates

    Science.gov (United States)

    Mattoni, G.; Zubko, P.; Maccherozzi, F.; van der Torren, A. J. H.; Boltje, D. B.; Hadjimichael, M.; Manca, N.; Catalano, S.; Gibert, M.; Liu, Y.; Aarts, J.; Triscone, J.-M.; Dhesi, S. S.; Caviglia, A. D.

    2016-11-01

    Nucleation processes of mixed-phase states are an intrinsic characteristic of first-order phase transitions, typically related to local symmetry breaking. Direct observation of emerging mixed-phase regions in materials showing a first-order metal-insulator transition (MIT) offers unique opportunities to uncover their driving mechanism. Using photoemission electron microscopy, we image the nanoscale formation and growth of insulating domains across the temperature-driven MIT in NdNiO3 epitaxial thin films. Heteroepitaxy is found to strongly determine the nanoscale nature of the phase transition, inducing preferential formation of striped domains along the terraces of atomically flat stepped surfaces. We show that the distribution of transition temperatures is a local property, set by surface morphology and stable across multiple temperature cycles. Our data provide new insights into the MIT of heteroepitaxial nickelates and point to a rich, nanoscale phenomenology in this strongly correlated material.

  15. Mott metal-insulator transition in the doped Hubbard-Holstein model

    Science.gov (United States)

    Kurdestany, Jamshid Moradi; Satpathy, S.

    2017-08-01

    Motivated by the current interest in the understanding of the Mott insulators away from half-filling, observed in many perovskite oxides, we study the Mott metal-insulator transition in the doped Hubbard-Holstein model using the Hartree-Fock mean field theory. The Hubbard-Holstein model is the simplest model containing both the Coulomb and the electron-lattice interactions, which are important ingredients in the physics of the perovskite oxides. In contrast to the half-filled Hubbard model, which always results in a single phase (either metallic or insulating), our results show that away from half-filling, a mixed phase of metallic and insulating regions occurs. As the dopant concentration is increased, the metallic part progressively grows in volume, until it exceeds the percolation threshold, leading to percolative conduction. This happens above a critical dopant concentration δc, which, depending on the strength of the electron-lattice interaction, can be a significant fraction of unity. This means that the material could be insulating even for a substantial amount of doping, in contrast to the expectation that doped holes would destroy the insulating behavior of the half-filled Hubbard model. While effects of fluctuation beyond the mean field remain an open question, our results provide a starting point for the understanding of the density-driven metal-insulator transition observed in many complex oxides.

  16. Impedance spectroscopy of Si whiskers in the range of metal-insulator transition

    Directory of Open Access Journals (Sweden)

    A. O. Druzinin

    2013-12-01

    Full Text Available Introduction. The paper deals with investigation of impedance spectroscopy of Si whiskers with doping concentration in the vicinity to metal-insulator transition in the region of low (4,2 – 70 K temperature and frequency range 0,01 – 250x103 Hz. Experimental results. The silicon whiskers were grown by chemical vapour deposition method in closed bromine system. The whiskers of 40x10-6 m in diameter have boron concentration from 2×1018 to 2×1019 сm-3. The impedance spectroscopy of Si whiskers was investigated with use of Lock-in amplifier in the region of low (4,2 – 70 K temperature and frequency range 0,01 – 250 x 103 Hz. The investigations showed that in the range of zone conductance (T= 30 – 70 K the whisker impedance has inductive character, while at the range of impurity conductance (T = 4,2 – 20 K impedance changes to capacity character. The reduction of impurity concentration at dielectric side of metal-insulator transition leads to decrease of the whisker capacity in the range of low temperatures. Discussion. An inductive character of whisker impedance is explained skin-effect of conductance in thin whisker, while capacity character of the whisker impedance is connected with hopping conductance on impurity band. Conclusions. Character of changes of Si whisker impedance conductance is discussed in the frame of hopping conductance on impurity band, which takes place at low temperatures.

  17. Electronic-structure evolution through the metal-insulator transition in RENiO{sub 3}.

    Energy Technology Data Exchange (ETDEWEB)

    Vobornik, I.; Perfetti, L.; Zacchingna, M.; Grioni, M.; Margaritondo, G.; Mesot, J.; Medarde, M.; Lacorre, P.; Materials Science Division; Inst. de physique Appliquee; Univ. du Maine

    1999-09-15

    We performed a photoemission investigation of the electronic structure of PrNiO{sub 3} and NdNiO{sub 3} through the first order (paramagnetic) metal to (antiferromagnetic) insulator transition. Surprisingly, the data reveal a temperature-dependent loss of spectral weight near the chemical potential, which extends well below the coincident metal-insulator (T{sub MI}) and magnetic (T{sub Neel}) transition temperatures. This is in contrast with the behavior in SmNiO{sub 3} and EuNiO{sub 3}, where the two transitions are separate. The spectral properties clearly indicate two distinct regimes for RNiO{sub 3} with T{sub MI}=T{sub Neel} and T{sub MI}>T{sub Neel}.

  18. Light scattering by epitaxial VO{sub 2} films near the metal-insulator transition point

    Energy Technology Data Exchange (ETDEWEB)

    Lysenko, Sergiy, E-mail: sergiy.lysenko@upr.edu; Fernández, Felix; Rúa, Armando; Figueroa, Jose; Vargas, Kevin; Cordero, Joseph [Department of Physics, University of Puerto Rico, Mayaguez, Puerto Rico 00681 (United States); Aparicio, Joaquin [Department of Physics, University of Puerto Rico-Ponce, Ponce, Puerto Rico 00732 (United States); Sepúlveda, Nelson [Department of Electrical and Computer Engineering, Michigan State University, East Lansing, Michigan 48824 (United States)

    2015-05-14

    Experimental observation of metal-insulator transition in epitaxial films of vanadium dioxide is reported. Hemispherical angle-resolved light scattering technique is applied for statistical analysis of the phase transition processes on mesoscale. It is shown that the thermal hysteresis strongly depends on spatial frequency of surface irregularities. The transformation of scattering indicatrix depends on sample morphology and is principally different for the thin films with higher internal elastic strain and for the thicker films where this strain is suppressed by introduction of misfit dislocations. The evolution of scattering indicatrix, fractal dimension, surface power spectral density, and surface autocorrelation function demonstrates distinctive behavior which elucidates the influence of structural defects and strain on thermal hysteresis, twinning of microcrystallites, and domain formation during the phase transition.

  19. Electronic Structure Evolution across the Peierls Metal-Insulator Transition in a Correlated Ferromagnet

    Directory of Open Access Journals (Sweden)

    P. A. Bhobe

    2015-10-01

    Full Text Available Transition metal compounds often undergo spin-charge-orbital ordering due to strong electron-electron correlations. In contrast, low-dimensional materials can exhibit a Peierls transition arising from low-energy electron-phonon-coupling-induced structural instabilities. We study the electronic structure of the tunnel framework compound K_{2}Cr_{8}O_{16}, which exhibits a temperature-dependent (T-dependent paramagnetic-to-ferromagnetic-metal transition at T_{C}=180  K and transforms into a ferromagnetic insulator below T_{MI}=95  K. We observe clear T-dependent dynamic valence (charge fluctuations from above T_{C} to T_{MI}, which effectively get pinned to an average nominal valence of Cr^{+3.75} (Cr^{4+}∶Cr^{3+} states in a 3∶1 ratio in the ferromagnetic-insulating phase. High-resolution laser photoemission shows a T-dependent BCS-type energy gap, with 2G(0∼3.5(k_{B}T_{MI}∼35  meV. First-principles band-structure calculations, using the experimentally estimated on-site Coulomb energy of U∼4  eV, establish the necessity of strong correlations and finite structural distortions for driving the metal-insulator transition. In spite of the strong correlations, the nonintegral occupancy (2.25 d-electrons/Cr and the half-metallic ferromagnetism in the t_{2g} up-spin band favor a low-energy Peierls metal-insulator transition.

  20. Entropic evidence for cooperation of multiple instabilities upon a metal-insulator transition in (EDO-TTF) 2PF 6

    Science.gov (United States)

    Saito, Kazuya; Ikeuchi, Satoaki; Ota, Akira; Yamochi, Hideki; Saito, Gunzi

    2005-01-01

    The entropy of the peculiar metal-insulator transition of the title compound was measured and analyzed, resulting in the conclusions that the mechanism of this transition is the catastrophic cooperation of multiple instabilities: Peierls instability, charge order and anion ordering.

  1. Stable metal-insulator transition in epitaxial SmNiO{sub 3} thin films

    Energy Technology Data Exchange (ETDEWEB)

    Ha, Sieu D., E-mail: sdha@seas.harvard.edu [School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138 (United States); Otaki, Miho; Jaramillo, R.; Podpirka, Adrian; Ramanathan, Shriram [School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138 (United States)

    2012-06-15

    Samarium nickelate (SmNiO{sub 3}) is a correlated oxide that exhibits a metal-insulator transition (MIT) above room temperature and is of interest for advanced electronics and optoelectronics. However, studies on SmNiO{sub 3} thin films have been limited to date, in part due to well-known difficulties in stabilizing the Ni{sup 3+} valence state during growth, which are manifested in non-reproducible electrical characteristics. In this work, we show that stable epitaxial SmNiO{sub 3} thin films can be grown by rf magnetron sputtering without extreme post-deposition annealing conditions using relatively high growth pressure (>200 mTorr). At low growth pressure, SmNiO{sub 3} is insulating and undergoes an irreversible MIT at {approx}430 K. As pressure is increased, films become metallic across a large temperature range from 100 to 420 K. At high pressure, films are insulating again but with a reversible and stable MIT at {approx}400 K. Phase transition properties can be continuously tuned by control of the sputtering pressure. - Graphical Abstract: X-ray diffraction (left) and resistivity-temperature characteristics (right) of sputtered SmNiO{sub 3} thin films as a function of sputtering pressure. As sputtering pressure increases, the out-of-plane lattice constant of SmNiO{sub 3} decreases, consistent with enhanced oxygen concentration. Concordantly, the electrical properties are strongly modified, and a reversible metal-insulator phase transition is observed at {approx}400 K in the film grown at high pressure. Highlights: Black-Right-Pointing-Pointer Stable SmNiO{sub 3} films grown by rf sputtering without extreme annealing conditions. Black-Right-Pointing-Pointer High sputtering pressures needed to fully stabilize SmNiO{sub 3}. Black-Right-Pointing-Pointer Reversible metal-insulator transition observed at {approx}400 K, similar to bulk. Black-Right-Pointing-Pointer Electrical properties strongly modifiable by varying sputtering pressure.

  2. Hund's coupling and the metal-insulator transition in the two-band Hubbard model

    Science.gov (United States)

    Pruschke, Th.; Bulla, R.

    2005-03-01

    The Mott-Hubbard metal-insulator transition is investigated in a two-band Hubbard model within dynamical mean-field theory. To this end, we use a suitable extension of Wilson’s numerical renormalization group for the solution of the effective two-band single-impurity Anderson model. This method is non-perturbative and, in particular, allows to take into account the full exchange part of the Hund’s rule coupling between the two orbitals. We discuss in detail the influence of the various Coulomb interactions on thermodynamic and dynamic properties, for both the impurity and the lattice model. The exchange part of the Hund’s rule coupling turns out to play an important role for the physics of the two-band Hubbard model and for the nature of the Mott-transition.

  3. Electrodynamics of the conducting polymer polyaniline on the insulating side of the metal-insulator transition

    Science.gov (United States)

    Helgren, Erik; Penney, Keith; Diefenbach, Matt; Longnickel, Maryna; Wainwright, Mark; Walker, Eldridge; Al-Azzawi, Sarah; Erhahon, Hendrix; Singley, Jason

    2017-03-01

    Conducting polymer samples of polyaniline (PANI) exhibit a dramatic change in their conductivity as a function of protonation level, analogous with the changes in the transport properties of semiconductors upon doping. In this paper, PANI samples were prepared by protonating with varying concentrations of hydrochloric acid. The complex terahertz frequency-dependent conductivity and the dc conductivity of these samples were measured and analyzed in the framework of the disorder-driven, metal-insulator quantum phase transition. The samples were determined to all fall in the insulating phase of this phase transition. The frequency dependence of both the real and imaginary terahertz conductivity are found to be consistent with theories that include electronic correlation effects.

  4. Metal-insulator transition in disordered systems from the one-body density matrix

    DEFF Research Database (Denmark)

    Olsen, Thomas; Resta, Raffaele; Souza, Ivo

    2017-01-01

    systems. In particular, for noninteracting systems the geometrical marker can be obtained from the configurational average of the norm-squared one-body density matrix, which can be calculated within open as well as periodic boundary conditions. This is in sharp contrast to a classification based...... on the static conductivity, which is only sensible within periodic boundary conditions. We exemplify the method by considering a simple lattice model, known to have a metal-insulator transition as a function of the disorder strength, and demonstrate that the transition point can be obtained accurately from...... the one-body density matrix. The approach has a general ab initio formulation and could in principle be applied to realistic disordered materials by standard electronic structure methods....

  5. Metal - Insulator Transition Driven by Vacancy Ordering in GeSbTe Phase Change Materials

    Science.gov (United States)

    Bragaglia, Valeria; Arciprete, Fabrizio; Zhang, Wei; Mio, Antonio Massimiliano; Zallo, Eugenio; Perumal, Karthick; Giussani, Alessandro; Cecchi, Stefano; Boschker, Jos Emiel; Riechert, Henning; Privitera, Stefania; Rimini, Emanuele; Mazzarello, Riccardo; Calarco, Raffaella

    2016-04-01

    Phase Change Materials (PCMs) are unique compounds employed in non-volatile random access memory thanks to the rapid and reversible transformation between the amorphous and crystalline state that display large differences in electrical and optical properties. In addition to the amorphous-to-crystalline transition, experimental results on polycrystalline GeSbTe alloys (GST) films evidenced a Metal-Insulator Transition (MIT) attributed to disorder in the crystalline phase. Here we report on a fundamental advance in the fabrication of GST with out-of-plane stacking of ordered vacancy layers by means of three distinct methods: Molecular Beam Epitaxy, thermal annealing and application of femtosecond laser pulses. We assess the degree of vacancy ordering and explicitly correlate it with the MIT. We further tune the ordering in a controlled fashion attaining a large range of resistivity. Employing ordered GST might allow the realization of cells with larger programming windows.

  6. Disorder-induced metal-insulator transition in cooled silver and copper nanoparticles: A statistical study

    Science.gov (United States)

    Medrano Sandonas, Leonardo; Landauro, Carlos V.

    2017-08-01

    The existence of a disorder-induced metal-insulator transition (MIT) has been proved in cooled silver and copper nanoparticles by using level spacing statistics. Nanoparticles are obtained by employing molecular dynamics simulations. Results show that structural disorder is not strong enough to affect their electronic character, and it remains in the metallic regime. Whereas, electronic properties cross to the insulating regime after increasing the chemical disorder strength, W / t . Then, based on scaling theory, we have found that the critical chemical disorder WC / t in which MIT happens for silver and copper nanoparticles are 24.0 ± 1.1 and 22.3 ± 0.9 , respectively. Its universality has also been studied.

  7. Surface antiferromagnetism and incipient metal-insulator transition in strained manganite films

    KAUST Repository

    Cossu, Fabrizio

    2013-06-21

    Using first-principles calculations, we show that the (001) surface of the ferromagnet La0.7Sr0.3MnO3 under an epitaxial compressive strain favors antiferromagnetic (AF) order in the surface layers, coexisting with ferromagnetic (FM) bulk order. Surface antiferromagnetism is accompanied by a very marked surface-related spectral pseudogap, signaling an incomplete metal-insulator transition at the surface. The different relaxation and rumpling of the MnO2 and LaO surface planes in the two competing magnetic phases cause distinct work-function changes, which are of potential diagnostic use. The AF phase is recognized as an extreme surface-assisted case of the combination of in-plane AF super-exchange and vertical FM double-exchange couplings that rules magnetism in manganites under in-plane compression.

  8. Metal-insulator transition in nanocomposite VO{sub x} films formed by anodic electrodeposition

    Energy Technology Data Exchange (ETDEWEB)

    Tsui, Lok-kun; Lu, Jiwei; Zangari, Giovanni, E-mail: gz3e@virginia.edu [Department of Materials Science and Engineering, University of Virginia, 395 McCormick Rd., Charlottesville, Virginia 22904 (United States); Hildebrand, Helga; Schmuki, Patrik [Department for Materials Science LKO, University of Erlangen-Nuremberg, Martensstr. 7, D-91058 Erlangen (Germany)

    2013-11-11

    The ability to grow VO{sub 2} films by electrochemical methods would open a low-cost, easily scalable production route to a number of electronic devices. We have synthesized VO{sub x} films by anodic electrodeposition of V{sub 2}O{sub 5}, followed by partial reduction by annealing in Ar. The resulting films are heterogeneous, consisting of various metallic/oxide phases and including regions with VO{sub 2} stoichiometry. A gradual metal insulator transition with a nearly two order of magnitude change in film resistance is observed between room temperature and 140 °C. In addition, the films exhibit a temperature coefficient of resistance of ∼ −2.4%/ °C from 20 to 140 °C.

  9. Mott metal-insulator transition in a metallic liquid - Gutzwiller molecular dynamics simulations

    Science.gov (United States)

    Barros, Kipton; Chern, Gia-Wei; Batista, Cristian D.; Kress, Joel D.; Kotliar, Gabriel

    2015-03-01

    Molecular dynamics (MD) simulations are crucial to modern computational physics, chemistry, and materials science, especially when combined with potentials derived from density-functional theory. However, even in state of the art MD codes, the on-site Coulomb repulsion is only treated at the self-consistent Hartree-Fock level. This standard approximation may miss important effects due to electron correlations. The Gutzwiller variational method captures essential correlated-electron physics yet is much faster than, e.g., the dynamical-mean field theory approach. We present our efficient Gutzwiller-MD implementation. With it, we investigate the Mott metal-insulator transition in a metallic fluid and uncover several surprising static and dynamic properties of this system.

  10. Percolative Metal-Insulator transition in the doped Hubbard-Holstein model with the Gutzwiller Approach

    Science.gov (United States)

    Moradi Kurdestany, Jamshid; Satpathy, Sashi

    Motivated by the recent progress in understanding of Mott insulators away from half filling, observed in many perovskite oxides, we study the metal-insulator transition in the Hubbard-Holstein model, which contains both the Coulomb and the electron-lattice (Jahn Teller) interactions by using the Gutzwiller variational method. We find that strong electron-lattice Interaction leads to phase separation, which however can be frustrated due to the long-range Coulomb interaction, resulting in a mixed phase consisting of puddles of metallic phases embedded in an insulating matrix. When the dopant concentration exceeds a threshold value xc , the metallic part forms a percolating network leading to metallic conduction. Depending on the strength of the electron-lattice interaction, xc can be of the order of 0.05 - 0.20 or so, which is the typical value observed in the perovskites.

  11. Phase coexistence and Mott metal-insulator transition in the doped Hubbard-Holstein model

    Science.gov (United States)

    Moradi Kurdestany, Jamshid; Satpathy, Sashi

    2015-03-01

    Motivated by recent progress in the understanding of the Mott insulators away from half filling [?], often observed in the oxide materials, we study the role of the electron-lattice interaction vis-à-vis the electron correlations by studying the one-band Hubbard-Holstein model using the Gutzwiller variational method. Our theory predicts phase separation for sufficiently strong electron-lattice interaction, which however is frustrated in the solid due to the long-range Coulomb interaction of the dopant atoms, resulting in puddles of metallic phases embedded in the insulating matrix. Metallic state occurs when the volume fraction of the metallic phase exceeds the percolation threshold, as the dopant concentration is increased. Connection is made with the experimentally observed metal-insulator transition in the complex oxides.

  12. Local Peltier-effect-induced reversible metal-insulator transition in VO2 nanowires

    Science.gov (United States)

    Takami, Hidefumi; Kanki, Teruo; Tanaka, Hidekazu

    2016-06-01

    We report anomalous resistance leaps and drops in VO2 nanowires with operating current density and direction, showing reversible and nonvolatile switching. This event is associated with the metal-insulator phase transition (MIT) of local nanodomains with coexistence states of metallic and insulating phases induced by thermoelectric cooling and heating effects. Because the interface of metal and insulator domains has much different Peltier coefficient, it is possible that a significant Peltier effect would be a source of the local MIT. This operation can be realized by one-dimensional domain configuration in VO2 nanowires because one straight current path through the electronic domain-interface enables theoretical control of thermoelectric effects. This result will open a new method of reversible control of electronic states in correlated electron materials.

  13. Microstructure and metal-insulator transition in single crystalline KMo4O6

    Directory of Open Access Journals (Sweden)

    Margareth Andrade

    2012-12-01

    Full Text Available High quality KMo4O6 single crystals with tetragonal structure (space group P4/mbm have been prepared by fused salt electrolysis. The crystals were studied by scanning electron microscopy (SEM, X-ray diffractometry, electrical resistivity, and magnetization measurements. X-ray powder diffraction patterns and SEM have given some information on the growth of single crystals. Electrical resistivity as a function of temperature shows that the KMo4O6 compound is a bad metal with resistivity change of approximately 30% in the temperature range from 2 to 300K. A metal-insulator transition (MIT, observed at approximately 110K, has been also confirmed for this material. Magnetization as a function of temperature agrees with previous report, however a magnetic ordering has been observed in M(H curves in the whole temperature range.

  14. Nonlocal Coulomb interactions and metal-insulator transition in Ti2O3: a cluster LDA+DMFT approach.

    NARCIS (Netherlands)

    Poteryaev, A.I.; Lichtenstein, A.I.; Kotliar, G.

    2004-01-01

    We present an ab initio quantum theory of the metal-insulator transition in Ti2O3. The recently developed cluster LDA+DMFT scheme is applied to describe the many-body features of this compound. The conventional single site DMFT cannot reproduce a low temperature insulating phase for any reasonable

  15. Ab initio study of metal-insulator transition in VO2

    Science.gov (United States)

    Zheng, Huihuo; Wagner, Lucas K.

    2013-03-01

    The structure distortion accompanied metal-insulator transition (MIT) of vanadium dioxide (VO2) at 340K has been a matter of ongoing controversy for near four decades. It is still unclear whether the nature of this transition is due to a Peierls instability, a Mott-Hubbard transition, or other physics. Most density functional theory based methods fail to describe the nature of the electronic state in this system, further complicating theoretical description of VO2. We will report on progress in applying the first principles diffusion quantum Monte Carlo method to the electronic structure of VO2 in the metallic and insulator phases. By examining the energetic properties, one particle reduced density matrix, as well as other static correlations in the two phases of the system, we will comment on which of the two common descriptions is a closer representation of the physical reality of VO2. This work was supported by the Strategic Research Initiatives project at Illinois(HZ) and NSF DMR 12-06242 (LKW).

  16. Metal-insulator transition and nanoscale phase separation in a hole-doped surface reconstruction

    Science.gov (United States)

    Mulugeta, Daniel; Snijders, Paul; Weitering, Hanno

    2014-03-01

    Doping, the deliberate introduction of impurities to alter electronic or magnetic properties, has been a tremendously successful method to study and understand systems with multiple competing interactions, as reflected in both the widespread use of doped semiconductors and in the large number of emergent electronic phases in doping-dependent phase diagrams of e.g. complex oxides. In low dimensional systems, however, the perturbation to the crystal lattice by the dopant atoms can overwhelm a delicate balance of interactions in e.g. a ground state with coexisting phases. Here we introduce a modulation doping technique used to dope holes in a surface reconstruction of Sn on Si(111). Using variable and low temperature scanning tunneling microscopy and spectroscopy, we observe a doping-induced metal-insulator phase transition that is of a displacive nature, contrasting with the order-disorder nature of other surface phase transitions. Moreover, the transition leads to an intrinsic nanoscale phase coexistence at 5 K never before observed on semiconductor surfaces. Clearly, modulation doping allows us to study the delicate balance of interactions in the phase diagram of low-dimensional electronic surface systems that is otherwise experimentally inaccessible. Funded by NSF DMR.

  17. Magnetic states, correlation effects and metal-insulator transition in FCC lattice

    Science.gov (United States)

    Timirgazin, M. A.; Igoshev, P. A.; Arzhnikov, A. K.; Irkhin, V. Yu

    2016-12-01

    The ground-state magnetic phase diagram (including collinear and spiral states) of the single-band Hubbard model for the face-centered cubic lattice and related metal-insulator transition (MIT) are investigated within the slave-boson approach by Kotliar and Ruckenstein. The correlation-induced electron spectrum narrowing and a comparison with a generalized Hartree-Fock approximation allow one to estimate the strength of correlation effects. This, as well as the MIT scenario, depends dramatically on the ratio of the next-nearest and nearest electron hopping integrals {{t}\\prime}/t . In contrast with metallic state, possessing substantial band narrowing, insulator one is only weakly correlated. The magnetic (Slater) scenario of MIT is found to be superior over the Mott one. Unlike simple and body-centered cubic lattices, MIT is the first order transition (discontinuous) for most {{t}\\prime}/t . The insulator state is type-II or type-III antiferromagnet, and the metallic state is spin-spiral, collinear antiferromagnet or paramagnet depending on {{t}\\prime}/t . The picture of magnetic ordering is compared with that in the standard localized-electron (Heisenberg) model.

  18. Percolative metal-insulator transition in LaMnO3

    Science.gov (United States)

    Sherafati, M.; Baldini, M.; Malavasi, L.; Satpathy, S.

    2016-01-01

    We show that the pressure-induced metal-insulator transition (MIT) in LaMnO3 is fundamentally different from the Mott-Hubbard transition and is percolative in nature, with the measured resistivity obeying the percolation scaling laws. Using the Gutzwiller method to treat correlation effects in a model Hamiltonian that includes both Coulomb and Jahn-Teller interactions, we show, one, that the MIT is driven by a competition between electronic correlation and the electron-lattice interaction, an issue that has been long debated, and two, that with compressed volume, the system has a tendency towards phase separation into insulating and metallic regions, consisting, respectively, of Jahn-Teller distorted and undistorted octahedra. This tendency manifests itself in a mixed phase of intermixed insulating and metallic regions in the experiment. Conduction in the mixed phase occurs by percolation and the MIT occurs when the metallic volume fraction, steadily increasing with pressure, exceeds the percolation threshold vc≈0.29 . Measured high-pressure resistivity follows the percolation scaling laws quite well, and the temperature dependence follows the Efros-Shklovskii variable-range hopping behavior for granular materials.

  19. Carbon kagome lattice and orbital-frustration-induced metal-insulator transition for optoelectronics.

    Science.gov (United States)

    Chen, Yuanping; Sun, Y Y; Wang, H; West, D; Xie, Yuee; Zhong, J; Meunier, V; Cohen, Marvin L; Zhang, S B

    2014-08-22

    A three-dimensional elemental carbon kagome lattice, made of only fourfold-coordinated carbon atoms, is proposed based on first-principles calculations. Despite the existence of 60° bond angles in the triangle rings, widely perceived to be energetically unfavorable, the carbon kagome lattice is found to display exceptional stability comparable to that of C(60). The system allows us to study the effects of triangular frustration on the electronic properties of realistic solids, and it demonstrates a metal-insulator transition from that of graphene to a direct gap semiconductor in the visible blue region. By minimizing s-p orbital hybridization, which is an intrinsic property of carbon, not only the band edge states become nearly purely frustrated p states, but also the band structure is qualitatively different from any known bulk elemental semiconductors. For example, the optical properties are similar to those of direct-gap semiconductors GaN and ZnO, whereas the effective masses are comparable to or smaller than those of Si.

  20. Metal-insulator transitions in LaTiO3 / CaTiO3 superlattices

    Science.gov (United States)

    Seo, Sung Seok A.; Lee, Ho Nyung

    2010-03-01

    Strongly correlated electrons at an interface of complex oxide heterostructures often show interesting behaviors that require an introduction of new physical concepts. For example, the metallic transport behavior found in the superlattices of a Mott insulator LaTiO3 and a band insulator SrTiO3 (STO) has established the concept of interfacial electronic reconstruction. In this work, we have studied the transport property of a new type of Mott/band insulator LaTiO3/CaTiO3 (LTO/CTO) superlattices grown by pulsed laser deposition (PLD). In order to rule out concerns about the PLD plume-triggered oxygen vacancies generated in STO substrates, which might influence transport measurement, and to investigate the effect of epitaxial strain, we have used insulating NdGaO3 substrates. While both LTO and CTO single films are highly insulating, we have observed intriguing metal-insulator transitions (MIT) in the LTO/CTO superlattices depending on the global LTO/CTO thickness ratio and temperature. (Note that LTO/STO superlattices are metallic at all temperatures (2-300 K)). In this talk, we will discuss the origin of the MIT in the scheme of self compensation mechanism of d-electrons at the hetero-interface between LTO and CTO.

  1. Metal-insulator transition and lattice instability of paramagnetic V{sub 2}O{sub 3}

    Energy Technology Data Exchange (ETDEWEB)

    Leonov, I.; Vollhardt, D. [Theoretical Physics III, Center for Electronic Correlations and Magnetism, University of Augsburg (Germany); Anisimov, V.I. [Institute of Metal Physics, Yekaterinburg (Russian Federation); Ural Federal University, Yekaterinburg (Russian Federation)

    2015-07-01

    We determine the electronic structure and phase stability of paramagnetic V{sub 2}O{sub 3} at the Mott-Hubbard metal-insulator phase transition, by employing a combination of ab initio methods for calculating band structures with dynamical mean-field theory. To explore structural transformations as a function of pressure, we use the experimentally determined atomic positions for the metallic and insulating phases, respectively, and calculate the total energy as a function of volume. We find that the structural stability depends very sensitively on changes of the lattice volume. The structural transformation associated with the metal-insulator transition is found to occur upon a slight expansion of the lattice volume by ∝ 1.5 %, in agreement with experiment. Our results show that the structural change precedes the metal-insulator transition, implying a complex interplay between electronic and lattice degrees of freedom at the transition. Electronic correlations and full charge self-consistency are found to be crucial for a correct description of the properties of V{sub 2}O{sub 3}.

  2. Monolayer MoS2 metal insulator transition based memcapacitor modeling with extension to a ternary device

    OpenAIRE

    Abdul Karim Khan; Byoung Hun Lee

    2016-01-01

    Memcapacitor model based on its one possible physical realization is developed and simulated in order to know its limitation before making a real device. The proposed device structure consists of vertically stacked dielectric layer and MoS2 monolayer between two external metal plates. The Metal Insulator Transition (MIT) phenomenon of MoS2 monolayer is represented in terms of percolation probabilty which is used as the system state. Cluster based site percolation theory is used to mimic the M...

  3. Origin of nonlinear transport across the magnetically induced superconductor-metal-insulator transition in two dimensions.

    Science.gov (United States)

    Seo, Y; Qin, Y; Vicente, C L; Choi, K S; Yoon, Jongsoo

    2006-08-04

    We have studied the effect of perpendicular magnetic fields and temperatures on nonlinear electronic transport in amorphous Ta superconducting thin films. The films exhibit a magnetic field-induced metallic behavior intervening the superconductor-insulator transition in the zero temperature limit. We show that the phase-identifying nonlinear transport in the superconducting and metallic phases arises from an intrinsic origin, not from an electron heating effect. The nonlinear transport is found to accompany an extraordinarily long voltage response time.

  4. Dynamics of the metal-insulator transition of donor-doped SrTi O3

    Science.gov (United States)

    Meyer, René; Zurhelle, Alexander F.; De Souza, Roger A.; Waser, Rainer; Gunkel, Felix

    2016-09-01

    The electrical properties of donor-doped SrTi O3 (n -STO) are profoundly affected by an oxidation-induced metal-insulator transition (MIT). Here we employ dynamical numerical simulations to examine the high-temperature MIT of n -STO over a large range of time and length scales. The simulations are based on the Nernst-Planck equations, the continuity equations, and the Poisson equation, in combination with surface lattice disorder equilibria serving as time-dependent boundary conditions. The simulations reveal that n -STO, upon oxidation, develops a kinetic space charge region (SCR) in the near-surface region. The surface concentrations of the variously mobile defects (electrons, Sr vacancies, and O vacancies) are found to vary over time and to differ considerably from the values of the new equilibrium. The formation of the SCR in which electrons are strongly depleted occurs within nanoseconds, i.e., it yields a fast MIT in the near-surface region during the oxidation process. As a result of charge (over-)compensation by Sr vacancies incorporated at the surface of n -STO, this SCR is much more pronounced than conventionally expected. In addition, we find an anomalous increase of O vacancy concentration at the surface upon oxidation caused by the SCR. Our simulations show that the SCR fades in the long term as a result of the slow in-diffusion of Sr vacancies. We discuss implications for the electrical conductivity of n -STO crystals used as substrates for epitaxial oxide thin films, of n -STO thin films and interfaces, and of polycrystalline n -STO with various functionalities.

  5. Suppression of Structural Phase Transition in VO2 by Epitaxial Strain in Vicinity of Metal-insulator Transition

    Science.gov (United States)

    Yang, Mengmeng; Yang, Yuanjun; Bin Hong; Wang, Liangxin; Hu, Kai; Dong, Yongqi; Xu, Han; Huang, Haoliang; Zhao, Jiangtao; Chen, Haiping; Song, Li; Ju, Huanxin; Zhu, Junfa; Bao, Jun; Li, Xiaoguang; Gu, Yueliang; Yang, Tieying; Gao, Xingyu; Luo, Zhenlin; Gao, Chen

    2016-03-01

    Mechanism of metal-insulator transition (MIT) in strained VO2 thin films is very complicated and incompletely understood despite three scenarios with potential explanations including electronic correlation (Mott mechanism), structural transformation (Peierls theory) and collaborative Mott-Peierls transition. Herein, we have decoupled coactions of structural and electronic phase transitions across the MIT by implementing epitaxial strain on 13-nm-thick (001)-VO2 films in comparison to thicker films. The structural evolution during MIT characterized by temperature-dependent synchrotron radiation high-resolution X-ray diffraction reciprocal space mapping and Raman spectroscopy suggested that the structural phase transition in the temperature range of vicinity of the MIT is suppressed by epitaxial strain. Furthermore, temperature-dependent Ultraviolet Photoelectron Spectroscopy (UPS) revealed the changes in electron occupancy near the Fermi energy EF of V 3d orbital, implying that the electronic transition triggers the MIT in the strained films. Thus the MIT in the bi-axially strained VO2 thin films should be only driven by electronic transition without assistance of structural phase transition. Density functional theoretical calculations further confirmed that the tetragonal phase across the MIT can be both in insulating and metallic states in the strained (001)-VO2/TiO2 thin films. This work offers a better understanding of the mechanism of MIT in the strained VO2 films.

  6. Field Effect and Strongly Localized Carriers in the Metal-Insulator Transition Material VO(2).

    Science.gov (United States)

    Martens, K; Jeong, J W; Aetukuri, N; Rettner, C; Shukla, N; Freeman, E; Esfahani, D N; Peeters, F M; Topuria, T; Rice, P M; Volodin, A; Douhard, B; Vandervorst, W; Samant, M G; Datta, S; Parkin, S S P

    2015-11-06

    The intrinsic field effect, the change in surface conductance with an applied transverse electric field, of prototypal strongly correlated VO(2) has remained elusive. Here we report its measurement enabled by epitaxial VO(2) and atomic layer deposited high-κ dielectrics. Oxygen migration, joule heating, and the linked field-induced phase transition are precluded. The field effect can be understood in terms of field-induced carriers with densities up to ∼5×10(13)  cm(-2) which are trongly localized, as shown by their low, thermally activated mobility (∼1×10(-3)  cm(2)/V s at 300 K). These carriers show behavior consistent with that of Holstein polarons and strongly impact the (opto)electronics of VO(2).

  7. Pressure-induced metal-insulator transition in spinel compound CuV{sub 2}S{sub 4}

    Energy Technology Data Exchange (ETDEWEB)

    Okada, H. [High Field Laboratory for Superconducting Materials, Institute for Materials Research, Tohoku University, Sendai 980-8577 (Japan)], E-mail: hironari@imr.tohoku.ac.jp; Koyama, K. [High Field Laboratory for Superconducting Materials, Institute for Materials Research, Tohoku University, Sendai 980-8577 (Japan); Hedo, M. [Faculty of Science, University of the Ryukyus, Okinawa 903-0213 (Japan); Uwatoko, Y. [Institute for Solid State Physics, University of Tokyo, Kashiwa, Chiba 277-8581 (Japan); Watanabe, K. [High Field Laboratory for Superconducting Materials, Institute for Materials Research, Tohoku University, Sendai 980-8577 (Japan)

    2008-04-01

    In order to investigate the pressure effect on electrical properties of CuV{sub 2}S{sub 4}, we performed the electrical resistivity measurements under high pressures up to 8 GPa for a high-quality polycrystalline sample. The charge density wave (CDW) transition temperatures increase with increasing pressure. The residual resistivity rapidly increases with increasing pressure over 4 GPa, and the temperature dependence of the electrical resistivity at 8 GPa exhibits a semiconducting behavior below about 150 K, indicating that a pressure-induced metal-insulator transition occurs in CuV{sub 2}S{sub 4} at 8 GPa.

  8. Two-dimensional metal-insulator transition as a strong localization induced crossover phenomenon

    Science.gov (United States)

    Das Sarma, S.; Hwang, E. H.

    2014-06-01

    Low-disorder and high-mobility two-dimensional (2D) electron (or hole) systems confined in semiconductor heterostructures undergo an apparent metal-insulator transition (MIT) at low temperatures as the carrier density (n) is varied. In some situations, the 2D MIT can be caused at a fixed low carrier density by changing an externally applied in-plane magnetic field parallel to the 2D layer. The goal of the current work is to obtain the critical density (nc) for the 2D MIT with the system being an effective metal (Anderson insulator) for density n above (below) nc. We study the 2D MIT phenomenon theoretically as a possible strong localization induced crossover process controlled by the Ioffe-Regel criterion, kFl=1, where kF(n) is the 2D Fermi wave vector and l (n) is the disorder-limited quantum mean free path on the metallic side. Calculating the quantum mean free path in the effective metallic phase from a realistic Boltzmann transport theory including disorder scattering effects, we solve the integral equation (with l depending on n through multidimensional integrals) defined by the Ioffe-Regel criterion to obtain the nonuniversal critical density nc as a function of the applicable physical experimental parameters including disorder strength, in-plane magnetic field, spin and valley degeneracy, background dielectric constant and carrier effective mass, and temperature. The key physics underlying the nonuniversal parameter dependence of the critical density is the density dependence of the screened Coulomb disorder. Our calculated results for the crossover critical density nc appear to be in qualitative and semiquantitative agreement with the available experimental data in different 2D semiconductor systems lending credence to the possibility that the apparent 2D MIT signals the onset of the strong localization crossover in disordered 2D systems. We also compare the calculated critical density obtained from the Ioffe-Regel criterion with that obtained from a

  9. Metal insulator transition with ferrimagnetic order in epitaxial thin films of spinel NiCo2O4

    Science.gov (United States)

    Silwal, Punam; Miao, Ludi; Stern, Ilan; Zhou, Xiaolan; Hu, Jin; Ho Kim, Dae

    2012-01-01

    We have grown epitaxial thin films of spinel NiCo2O4 on single crystalline MgAl2O4 (001) substrates by pulsed laser deposition. Magnetization measurement revealed hysteresis loops consistent with the reported ferrimagnetic order. The electrical transport exhibits a metallic behavior with the lowest resistivity of 0.8 mΩ cm and a metal insulator transition around the Néel temperature. The systematic variation in the properties of the films grown at different growth temperatures indicates a close relationship between the magnetic order and electrical transport.

  10. Electric controlling of surface metal-insulator transition in the doped BaTiO3 film

    Science.gov (United States)

    Xun, Wei; Hao, Xiang; Pan, Tao; Zhong, Jia-Lin; Ma, Chun-Lan; Hou, Fang; Wu, Yin-Zhong

    2017-07-01

    Based on first-principles calculations, the BaTiO3(BTO) film with local La-doping is studied. For a selected concentration and position of doping, the surface metal-insulator transition occurs under the applied electric field, and the domain appears near the surface for both bipolar states. Furthermore, for the insulated surface state, i.e., the downward polarization state in the doped film, the gradient bandgap structure is achieved, which favors the absorption of solar energy. Our investigation can provide an alternative avenue in modification of surface property and surface screening effect in polar materials.

  11. Electric controlling of surface metal-insulator transition in the doped BaTiO3 film

    Directory of Open Access Journals (Sweden)

    Wei Xun

    2017-07-01

    Full Text Available Based on first-principles calculations, the BaTiO3(BTO film with local La-doping is studied. For a selected concentration and position of doping, the surface metal-insulator transition occurs under the applied electric field, and the domain appears near the surface for both bipolar states. Furthermore, for the insulated surface state, i.e., the downward polarization state in the doped film, the gradient bandgap structure is achieved, which favors the absorption of solar energy. Our investigation can provide an alternative avenue in modification of surface property and surface screening effect in polar materials.

  12. Metal-Insulator Phase Transition in thin VO2 films: A Look from the Far Infrared Side

    DEFF Research Database (Denmark)

    Jepsen, Peter Uhd; Fischer, B. M.; Thoman, A.

    Terahertz Time-Domain Spectroscopy (THz-TDS) to investigate theoptical properties of laser-ablated VO2 films in the vicinity of the MI transition in the 0.1-2 THz frequency range. At frequencies below the phonon resonances of the material wecan obtain a clean spectroscopic signature of the carrier dynamics......Vanadium dioxide (VO2) displays a well-known metal-insulator (MI) transition at atemperature of 68oC. The MI transition in VO2 has been studied extensively by a widerange of optical, electrical, structural, and magnetic measurements. In spite of this there isstill some controversy about the nature...... of the phase transition. Mid-IR studies1 indicatethat a model based on growth of metallic domains accounts for the phase transitionwhereas other studies2 argue that a homogeneous increase of the carrier concentration isresponsible for the change in properties across the phase transition.In this study we use...

  13. Oxygen Vacancy Induced Room-Temperature Metal-Insulator Transition in Nickelate Films and Its Potential Application in Photovoltaics.

    Science.gov (United States)

    Wang, Le; Dash, Sibashisa; Chang, Lei; You, Lu; Feng, Yaqing; He, Xu; Jin, Kui-juan; Zhou, Yang; Ong, Hock Guan; Ren, Peng; Wang, Shiwei; Chen, Lang; Wang, Junling

    2016-04-20

    Oxygen vacancy is intrinsically coupled with magnetic, electronic, and transport properties of transition-metal oxide materials and directly determines their multifunctionality. Here, we demonstrate reversible control of oxygen content by postannealing at temperature lower than 300 °C and realize the reversible metal-insulator transition in epitaxial NdNiO₃ films. Importantly, over 6 orders of magnitude in the resistance modulation and a large change in optical bandgap are demonstrated at room temperature without destroying the parent framework and changing the p-type conductive mechanism. Further study revealed that oxygen vacancies stabilized the insulating phase at room temperature is universal for perovskite nickelate films. Acting as electron donors, oxygen vacancies not only stabilize the insulating phase at room temperature, but also induce a large magnetization of ∼50 emu/cm³ due to the formation of strongly correlated Ni²⁺ t(2g)⁶e(g)² states. The bandgap opening is an order of magnitude larger than that of the thermally driven metal-insulator transition and continuously tunable. Potential application of the newly found insulating phase in photovoltaics has been demonstrated in the nickelate-based heterojunctions. Our discovery opens up new possibilities for strongly correlated perovskite nickelates.

  14. Interplay between Ferroelastic and Metal-Insulator Phase Transitions in Strained Quasi-Two-Dimensional VO2 Nanoplatelets

    Energy Technology Data Exchange (ETDEWEB)

    Tselev, Alexander [ORNL; Strelcov, Evgheni [Southern Illinois University; Luk' yanchuk, Prof. Igor A. [University of Picardie Jules Verne, Amiens, France; Ivanov, Ilia N [ORNL; Budai, John D [ORNL; Tischler, Jonathan Zachary [ORNL; Jones, Keith M [ORNL; Proksch, Roger [Asylum Research, Santa Barbara, CA; Kalinin, Sergei V [ORNL; Kolmakov, Andrei [ORNL

    2010-01-01

    Formation of ferroelastic twin domains in VO_2 nanosystems can strongly affect local strain distributions, and hence couple to the strain-controlled metal-insulator transition. Here we report polarized-light optical and scanning microwave microscopy studies of interrelated ferroelastic and metal-insulator transitions in single-crystalline vanadium dioxide (VO_2) quasi-two-dimensional (quasi-2D) nanoplatelets (NPls). In contrast to quasi-1D single-crystalline nanobeams, the geometric frustration results in emergence of several possible families of ferroelastic domains in NPls, thus allowing systematic studies of strain-controlled transitions in the presence of geometrical frustration. We demonstrate possibility of controlling the ferroelastic domain population by the strength of the NPl-substrate interaction, mechanical stress, and by the NPl lateral size. Ferroelastic domain species and domain walls are identified based on standard group-theoretical considerations. Using variable temperature microscopy, we imaged the development of domains of metallic and semiconducting phases during the metal-insulator phase transition and non-trivial strain-driven reentrant domain formation. A long-range reconstruction of ferroelastic structures accommodating metal-insulator domain formation has been observed. These studies illustrate that complete picture of the phase transitions in single-crystalline and disordered VO_2 structures can be drawn only if both ferroelastic and metal-insulator strain effects are taken into consideration and understood.

  15. Metal-Insulator Transition and Superconductivity in Spinel-Type System Cu 1-xZnxIr 2S 4

    Science.gov (United States)

    Suzuki, Hiroyuki; Furubayashi, Takao; Cao, Guanghan; Kitazawa, Hideaki; Kamimura, Akira; Hirata, Kazuto; Matsumoto, Takehiko

    1999-08-01

    The thiospinel compoundCuIr2S4 exhibits the metal-insulator (M-I) transitionaccompanied by the structural transition. In this work, compounds ofCu1-xZnxIr2S4 in the composition range 0≤x≤0.5 were synthesized to examine the effects of excess electronssupplied by replacing Cu with Zn. The samples were investigated bymeasurements of X-ray diffraction, electrical resistance and magneticsusceptibility. The M-I transition temperature T MIdecreases with increasing x. Results are discussed on the basis ofthe model of charge ordering for the insulating state. It was foundthat the samples with x≥0.3 show no M-I transition and exhibitsuperconductivity. The transition temperature T C is 2.8 Kfor x= 0.3 and 2.2 K for x= 0.5. The ground state of the systemchanges from insulating to superconducting with increasing Zncontent.

  16. Elastic behavior around metal-insulator transition in PrRu{sub 4}P{sub 12}

    Energy Technology Data Exchange (ETDEWEB)

    Nakanishi, Y. [Department of Materials Science and Engineering, Iwate University, Morioka 020-8551 (Japan)]. E-mail: yoshiki@iwate-u.ac.jp; Kumagai, T. [Department of Materials Science and Engineering, Iwate University, Morioka 020-8551 (Japan); Oikawa, M. [Department of Materials Science and Engineering, Iwate University, Morioka 020-8551 (Japan); Saha, S.R. [Department of Physics, Tokyo Metropolitan University, Hachioji 192-0397 (Japan); Sugawara, H. [Department of Physics, Tokyo Metropolitan University, Hachioji 192-0397 (Japan); Sato, H. [Department of Physics, Tokyo Metropolitan University, Hachioji 192-0397 (Japan); Yoshizawa, M. [Department of Materials Science and Engineering, Iwate University, Morioka 020-8551 (Japan)

    2006-03-15

    Elastic properties of PrRu{sub 4}P{sub 12} have been investigated by means of the ultrasonic measurement. A clear bend was observed in elastic constants C{sub 11} (C{sub 11}-C{sub 12})/2 and C{sub 44} at metal-insulator transition temperature T{sub MI} of 62.3K. Furthermore, C{sub 11}, and (C{sub 11}-C{sub 12})/2 exhibits a pronounced elastic softening towards low temperature in the temperature range down to 1.5K. This fact suggests strongly that Pr{sup 3+}{gamma}{sub 3} non-Kramers doublet ground state is realized in PrRu{sub 4}P{sub 12} under the crystalline electric field (CEF) potential. This also suggests that an orbital degree of freedom still remains below T{sub MI} and a quadrupolar ordering has nothing to do with the metal-insulator transition. The elastic property and 4f ground state of Pr ions in this system will be discussed from the view point of CEF effect.

  17. Bond formation effects on the metal-insulator transition in the half-filled kagome Hubbard model

    Science.gov (United States)

    Higa, Ryota; Asano, Kenichi

    2016-06-01

    We study the metal-insulator transition in the half-filled Hubbard model on a Kagome lattice using the variational cluster approximation. The strong coupling limit of the model corresponds to the S =1 /2 Kagome Heisenberg antiferromagnet, which is known to have a singlet ground state, although its detail is still debated. As the results of the cluster methods generally depend much on the choice of the unit cluster, we have chosen the clusters that are compatible with these singlet ground states in the strong coupling case found so far, which basically consist of even number of sites. It is found that the correlated electrons on the Kagome lattice have a strong tendency to form valence-bond structures, which are the resonation of electrons on a single bond or several bonds forming loops. The zero-temperature metal-insulator transition at some interaction strength is possibly driven by the formation of such short range valence bonds and shows a second order character, which is distinctive from the Brinkman-Rice scenario. The electrons on these valence bonds further localizes onto each site as the interaction increases, and the valence bonds of electrons finally turn into magnetic singlet bonds between localized S =1 /2 spins, which are consistent with the ground states of the Kagome antiferromagnet.

  18. Structural distortion on metal-insulator transition in ordered double perovskite Ca sub 2 FeReO sub 6

    CERN Document Server

    Oikawa, K; Kato, H; Tokura, Y

    2003-01-01

    The crystal and magnetic structures of an ordered double perovskite, Ca sub 2 FeReO sub 6 , were studied by high-resolution neutron powder diffraction as a function of the temperature from 7 K to 550 K. All of the diffraction data were precisely refined by the Rietveld method, and we confirmed a structural phase transition at around 140 K where the metal-insulator transition occurs from ferrimagnetic metal (FM) to ferrimagnetic insulator (FI) phases. At this temperature, there exists a change in the distortion direction of [ReO sub 6] octahedra together with a spin reorientation, which strongly supports the occurrence of orbital ordering of the t sub 2 sub g electrons. FM and FI phases coexist in a narrow temperature range at around 140 K, which is typically seen in the first-order phase transition. A phase separation was not detected in our well-characterized sample. (author)

  19. Modulation of metal-insulator transitions by field-controlled strain in NdNiO3/SrTiO3/PMN-PT (001) heterostructures

    Science.gov (United States)

    Heo, Seungyang; Oh, Chadol; Eom, Man Jin; Kim, Jun Sung; Ryu, Jungho; Son, Junwoo; Jang, Hyun Myung

    2016-02-01

    The band width control through external stress has been demonstrated as a useful knob to modulate metal-insulator transition (MIT) in RNiO3 as a prototype correlated materials. In particular, lattice mismatch strain using different substrates have been widely utilized to investigate the effect of strain on transition temperature so far but the results were inconsistent in the previous literatures. Here, we demonstrate dynamic modulation of MIT based on electric field-controlled pure strain in high-quality NdNiO3 (NNO) thin films utilizing converse-piezoelectric effect of (001)-cut - (PMN-PT) single crystal substrates. Despite the difficulty in the NNO growth on rough PMN-PT substrates, the structural quality of NNO thin films has been significantly improved by inserting SrTiO3 (STO) buffer layers. Interestingly, the MIT temperature in NNO is downward shifted by ~3.3 K in response of 0.25% in-plane compressive strain, which indicates less effective TMI modulation of field-induced strain than substrate-induced strain. This study provides not only scientific insights on band-width control of correlated materials using pure strain but also potentials for energy-efficient electronic devices.

  20. Magnetic and metal-insulator transitions in coupled spin-fermion systems

    Science.gov (United States)

    Mondaini, R.; Paiva, T.; Scalettar, R. T.

    2014-10-01

    We use quantum Monte Carlo method to determine the magnetic and transport properties of coupled square lattice spin and fermionic planes as a model for a metal-insulator interface. Specifically, layers of Ising spins with an intralayer exchange constant J interact with the electronic spins of several adjoining metallic sheets via a coupling JH. When the chemical potential cuts across the band center, that is, at half-filling, the Néel temperature of antiferromagnetic (J >0) Ising spins is enhanced by the coupling to the metal, while in the ferromagnetic case (J interface increases, and also exhibits a nonmonotonic dependence on JH. For doped lattices, an interesting charge disproportionation occurs where electrons move to the interface layer to maintain half-filling there.

  1. Transferring MBE-grown topological insulator films to arbitrary substrates and metal-insulator transition via Dirac gap.

    Science.gov (United States)

    Bansal, Namrata; Cho, Myung Rae; Brahlek, Matthew; Koirala, Nikesh; Horibe, Yoichi; Chen, Jing; Wu, Weida; Park, Yun Daniel; Oh, Seongshik

    2014-03-12

    Mechanical exfoliation of bulk crystals has been widely used to obtain thin topological insulator (TI) flakes for device fabrication. However, such a process produces only microsized flakes that are highly irregular in shape and thickness. In this work, we developed a process to transfer the entire area of TI Bi2Se3 thin films grown epitaxially on Al2O3 and SiO2 to arbitrary substrates, maintaining their pristine morphology and crystallinity. Transport measurements show that these transferred films have lower carrier concentrations and comparable or higher mobilities than before the transfer. Furthermore, using this process we demonstrated a clear metal-insulator transition in an ultrathin Bi2Se3 film by gate-tuning its Fermi level into the hybridization gap formed at the Dirac point. The ability to transfer large area TI films to any substrate will facilitate fabrication of TI heterostructure devices, which will help explore exotic phenomena such as Majorana fermions and topological magnetoelectricity.

  2. The metal-insulator transition of RNiO{sub 3} perovskites. What can we learn from neutron diffraction?

    Energy Technology Data Exchange (ETDEWEB)

    Medarde, M.L. [Paul Scherrer Inst. (PSI), Villigen (Switzerland)

    1996-11-01

    RNiO{sub 3} perovskites (R = rare earth) provide a remarkable opportunity to study the relationship between structural and physical properties since by moving along the 4f rare earth series, the evolution of several transport and magnetic properties can be nicely correlated to the steric effects associated with the lanthanide contraction. The most appealing example is probably the metal-insulator transition discovered for the compounds with R{ne}La, whose critical temperature T{sub M-I} increases with decreasing size of the rare earth ion. In this lecture, a summary of the most relevant neutron diffraction results on this system is presented. Moreover, the nickelates are used as an example to illustrate the performance of the diffractometers HRPT and DMCG to be installed at the SINQ. (author) 12 figs., 2 tabs., 17 refs.

  3. Resistivity of the insulating phase approaching the two-dimensional metal-insulator transition: The effect of spin polarization

    Science.gov (United States)

    Li, Shiqi; Sarachik, M. P.

    2017-01-01

    The resistivities of the dilute, strongly interacting two-dimensional electron systems in the insulating phase of a silicon MOSFET are the same for unpolarized electrons in the absence of magnetic field and for electrons that are fully spin polarized by the presence of an in-plane magnetic field. In both cases the resistivity obeys Efros-Shklovskii variable range hopping ρ (T ) =ρ0exp[(TES/T ) 1 /2] , with TE S and 1 /ρ0 mapping onto each other if one applies a shift of the critical density nc reported earlier. With and without magnetic field, the parameters TE S and 1 /ρ0=σ0 exhibit scaling consistent with critical behavior approaching a metal-insulator transition.

  4. Tuning directional dependent metal-insulator transitions in quasi-1D quantum wires with spin-orbit density wave instability

    Science.gov (United States)

    Das, Tanmoy

    2016-07-01

    We study directional dependent band gap evolutions and metal-insulator transitions (MITs) in model quantum wire systems within the spin-orbit density wave (SODW) model. The evolution of MIT is studied as a function of varying anisotropy between the intra-wire hopping ({{t}\\parallel} ) and inter-wire hopping ({{t}\\bot} ) with Rashba spin-orbit coupling. We find that as long as the anisotropy ratio (β ={{t}\\bot}/{{t}\\parallel} ) remains below 0.5, and the Fermi surface nesting is tuned to {{\\mathbf{Q}}1}=≤ft(π,0\\right) , an exotic SODW induced MIT easily develops, with its critical interaction strength increasing with increasing anisotropy. As β \\to 1 (2D system), the nesting vector switches to {{\\mathbf{Q}}2}=≤ft(π,π \\right) , making this state again suitable for an isotropic MIT. Finally, we discuss various physical consequences and possible applications of the directional dependent MIT.

  5. Joule Heating-Induced Metal-Insulator Transition in Epitaxial VO2/TiO2 Devices.

    Science.gov (United States)

    Li, Dasheng; Sharma, Abhishek A; Gala, Darshil K; Shukla, Nikhil; Paik, Hanjong; Datta, Suman; Schlom, Darrell G; Bain, James A; Skowronski, Marek

    2016-05-25

    DC and pulse voltage-induced metal-insulator transition (MIT) in epitaxial VO2 two terminal devices were measured at various stage temperatures. The power needed to switch the device to the ON-state decrease linearly with increasing stage temperature, which can be explained by the Joule heating effect. During transient voltage induced MIT measurement, the incubation time varied across 6 orders of magnitude. Both DC I-V characteristic and incubation times calculated from the electrothermal simulations show good agreement with measured values, indicating Joule heating effect is the cause of MIT with no evidence of electronic effects. The width of the metallic filament in the ON-state of the device was extracted and simulated within the thermal model.

  6. Metal-Insulator Transition and Superconductivity in Y1-xPr(Ce)xBa2Cu3O7

    Institute of Scientific and Technical Information of China (English)

    韩汝珊; 苏肇冰; 王玉鹏

    1994-01-01

    To interpret the metal-insulator transition and depression of Tc induced by Pr-and Ce-doping in YBa2Cu3O7, we propose a model of mixed local hole states which describe a strong admixture of 4f1 state with states of 4f2 plus a hole in the CuO2 planes for Y1-x-Prx-07 and 4f0 state with states of 4f1 plus a hole in Y1-xCex-O7. Our model resolves the controversy between the magnetic and spectroscopic measurements. As a natural consequence, most of the experimental results on Y1-xPrx-O7 can be explained and certain properties of Y1-xCex-O7 are predicted. The critical doping density of Pr will take the value of xc ≈0.5.

  7. Anisotropic phase separation through the metal-insulator transition in amorphous Mo-Ge and Fe-Ge alloys

    Energy Technology Data Exchange (ETDEWEB)

    Regan, M.J.

    1993-12-01

    Since an amorphous solid is often defined as that which lacks long-range order, the atomic structure is typically characterized in terms of the high-degree of short-range order. Most descriptions of vapor-deposited amorphous alloys focus on characterizing this order, while assuming that the material is chemically homogeneous beyond a few near neighbors. By coupling traditional small-angle x-ray scattering which probes spatial variations of the electron density with anomalous dispersion which creates a species-specific contrast, one can discern cracks and voids from chemical inhomogeneity. In particular, one finds that the chemical inhomogeneities which have been previously reported in amorphous Fe{sub x}Ge{sub 1-x} and Mo{sub x}Ge{sub 1-x} are quite anisotropic, depending significantly on the direction of film growth. With the addition of small amounts of metal atoms (x<0.2), no films appear isotropic nor homogeneous through the metal/insulator transition. The results indicate that fluctuations in the growth direction play a pivotal role in preventing simple growth models of a columnar structure or one that evolves systematically as it grows. The anomalous scattering measurements identify the metal atoms (Fe or Mo) as the source of the anisotropy, with the Ge atoms distributed homogeneously. The author has developed a method for using these measurements to determine the compositions of the phase-separating species. The results indicate phase separation into an amorphous Ge and an intermetallic phase of stoichiometry close to FeGe{sub 2} or MoGe{sub 3}. Finally, by manipulating the deposited power flux and rates of growth, Fe{sub x}Ge{sub 1-x} films which have the same Fe composition x can be grown to different states of phase separation. These results may help explain the difficulty workers have had in isolating the metal/insulator transition for these and other vapor-deposited amorphous alloys.

  8. Metal-insulator transition in Si(111)-(4 x 1)/(8 x 2)-In studied by optical spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Speiser, E.; Hinrichs, K.; Cobet, C.; Esser, N. [Leibniz-Institut fuer Analytische Wissenschaften - ISAS - e.V., Albert-Einstein-Str. 9, 12489 Berlin (Germany); Chandola, S. [Leibniz-Institut fuer Analytische Wissenschaften - ISAS - e.V., Albert-Einstein-Str. 9, 12489 Berlin (Germany); School of Physics, Trinity College Dublin 2 (Ireland); Gensch, M. [Helmholtz Zentrum Berlin (Germany); Wippermann, S.; Schmidt, W.G. [Theoretische Physik, Universitaet Paderborn (Germany); Bechstedt, F. [Institut fuer Festkoerpertheorie und -Optik, Friedrich-Schiller-Universitaet, Jena (Germany); Richter, W. [Dipartimento di Fisica, Universita di Roma Tor Vergata, Via della Ricerca Scientifica 1, 00133 Roma (Italy); Fleischer, K.; McGilp, J.F. [School of Physics, Trinity College Dublin 2 (Ireland)

    2010-08-15

    Measurements of the surface vibrational modes and optical response of Si(111)-(4 x 1)/(8 x 2)-In are compiled and a comparison to ab initio calculations performed within DFT-LDA formalism is given. Surface resonant Raman spectroscopy allows identifying a number of surface phonons with high spectral precision. The phase transition of the (4 x 1)-(8 x 2) surface structure is found to be accompanied by characteristic changes of the surface phonons, which are discussed with respect to various structural models suggested. The optical anisotropy of the (8 x 2) phase shows that the anisotropic Drude tail of the (4 x 1) phase is replaced by two peaks at 0.50 and 0.72 eV. The spectroscopic signatures of the (4 x 1) and (8 x 2) phases agree with a metal-insulator transition. The mid-IR-anisotropic optical response of the insulating (8 x 2) phase is interpreted in terms of electronic single particle excitations between surface electronic bands related to the In-nanowire surface. Comparison of the measured optical transitions with DFT ab initio calculations for the hexagon model and the trimer model of the (8 x 2) structure shows evidence for the existence of the hexagon structure. (Abstract Copyright [2010], Wiley Periodicals, Inc.)

  9. Monolayer MoS2 metal insulator transition based memcapacitor modeling with extension to a ternary device

    Science.gov (United States)

    Khan, Abdul Karim; Lee, Byoung Hun

    2016-09-01

    Memcapacitor model based on its one possible physical realization is developed and simulated in order to know its limitation before making a real device. The proposed device structure consists of vertically stacked dielectric layer and MoS2 monolayer between two external metal plates. The Metal Insulator Transition (MIT) phenomenon of MoS2 monolayer is represented in terms of percolation probabilty which is used as the system state. Cluster based site percolation theory is used to mimic the MIT of MoS2 which shows slight discontinuous change in MoS2 monolayer conductivity. The metal to insulator transition switches the capacitance of the device in hysterical way. An Ioffe Regel criterion is used to determine the MIT state of MoS2 monolayer. A good control of MIT time in the range of psec is also achieved by changing a single parameter in the model. The model shows memcapacitive behavior with an edge of fast switching (in psec range) over the previous general models. The model is then extended into vertical cascaded version which behaves like a ternary device instead of binary.

  10. Monolayer MoS2 metal insulator transition based memcapacitor modeling with extension to a ternary device

    Directory of Open Access Journals (Sweden)

    Abdul Karim Khan

    2016-09-01

    Full Text Available Memcapacitor model based on its one possible physical realization is developed and simulated in order to know its limitation before making a real device. The proposed device structure consists of vertically stacked dielectric layer and MoS2 monolayer between two external metal plates. The Metal Insulator Transition (MIT phenomenon of MoS2 monolayer is represented in terms of percolation probabilty which is used as the system state. Cluster based site percolation theory is used to mimic the MIT of MoS2 which shows slight discontinuous change in MoS2 monolayer conductivity. The metal to insulator transition switches the capacitance of the device in hysterical way. An Ioffe Regel criterion is used to determine the MIT state of MoS2 monolayer. A good control of MIT time in the range of psec is also achieved by changing a single parameter in the model. The model shows memcapacitive behavior with an edge of fast switching (in psec range over the previous general models. The model is then extended into vertical cascaded version which behaves like a ternary device instead of binary.

  11. Effects of porous nano-structure on the metal-insulator transition in VO{sub 2} films

    Energy Technology Data Exchange (ETDEWEB)

    Xu Yuanjie [College of Materials Science and Engineering, Sichuan University, Chengdu 610064, Sichuan (China); Huang Wanxia, E-mail: huangwanxiascu@yahoo.com.cn [College of Materials Science and Engineering, Sichuan University, Chengdu 610064, Sichuan (China); Shi Qiwu; Zhang Yang; Zhang Yubo; Song Linwei [College of Materials Science and Engineering, Sichuan University, Chengdu 610064, Sichuan (China); Zhang Yaxin [Terahertz Science and Technology Research Center, University of Electronic Science and Technology of China, Chengdu 610054, Sichuan (China)

    2012-10-15

    Graphical abstract: The picture shows the morphology and hysteresis loop of porous VO{sub 2} film: porous nano-structure with small nanoparticles is obtained, transition temperature is reduced to 56 Degree-Sign C and hysteresis width is increased to 36 Degree-Sign C. Highlights: Black-Right-Pointing-Pointer VO{sub 2} films with small nanoparticles and homogeneous pores are obtained. Black-Right-Pointing-Pointer T{sub t} of porous nano-structure VO{sub 2} film is reduced to 56 Degree-Sign C and {Delta}T is increased to 36 Degree-Sign C. Black-Right-Pointing-Pointer Systematic study of CTAB concentration on morphology and MIT properties of the VO{sub 2} films is conducted. - Abstract: In this work, we confirmed experimentally that the porous nano-structure of vanadium dioxide (VO{sub 2}) films had significant effects on the features of the metal-insulator transition. Porous VO{sub 2} films had been synthesized on mica substrates via a simple solution process with inorganic precursor and cetyltrimethyl ammonium bromide (CTAB). SEM images showed a combination of homogenously distributed pores and VO{sub 2} nanoparticles. Metal to insulator transition (MIT) characteristics measurements revealed that, the porous nano-structure VO{sub 2} films had low transition temperature, wide hysteresis width and gentle slopes of hysteresis loop. Morphologies and MIT characteristics of the films could be controlled by simply varying CTAB concentration, which is of great importance in achieving practical applications.

  12. Variable-range hopping conduction and metal-insulator transition in amorphous RexSi1-x thin films

    Science.gov (United States)

    Lisunov, K. G.; Vinzelberg, H.; Arushanov, E.; Schumann, J.

    2011-09-01

    Resistivity, ρ(T), of the amorphous RexSi1-x thin films with x = 0.285-0.351 is investigated in the interval of T ~ 300-0.03 K. At x = 0.285-0.324 the activated behavior of ρ(T) is governed by the Mott and the Shklovskii-Efros variable-range hopping (VRH) conduction mechanisms in different temperature intervals and the three-dimensional regime of the hopping. Between x = 0.328 and 0.351 the activationless dependence of ρ(T) takes place. The critical behavior of the characteristic VRH temperatures and of the Coulomb gap, Δ, pertinent to proximity to the metal-insulator transition at the critical value of xc ≈ 0.327, is observed. The analysis of the critical behavior of Δ yields directly the critical exponent of the dielectric permittivity, η = 2.1 ± 0.2, in agreement with the theoretical prediction, η = 2. On the other hand, the values of the critical exponent of the correlation length ν ~ 0.8-1.1 close to the expected value of unity can be obtained from the analysis of the critical behavior of the VRH characteristic temperatures under an additional assumption of a strong underbarrier scattering of hopping charge carriers in conditions, when the concentration of scattering centers considerably exceeds the concentration of sites involved in the hopping.

  13. Realization of metal-insulator transition and oxidation in silver nanowire percolating networks by terahertz reflection spectroscopy.

    Science.gov (United States)

    Tsai, Yao-Jiun; Chang, Chi-Ying; Lai, Yi-Chun; Yu, Pei-Chen; Ahn, Hyeyoung

    2014-01-08

    Metal nanowires (NWs) enable versatile applications in printed electronics and optoelectronics by serving as thin and flexible transparent electrodes. The performance of metal NWs as thin electrodes is highly correlated to the connectivity of NW meshes. The percolation threshold of metal NW films corresponds to the minimum density of NWs to form the transparent, yet conductive metal NW networks. Here, we determine the percolation threshold of silver NW (AgNW) networks by using morphological analysis and terahertz (THz) reflection spectroscopy. From the divergent behavior of carrier scattering time and the increase of carrier backscattering factor, the critical NW density at which crossover from Drude to non-Drude behavior of THz conductivity occurs can be unambiguously determined for AgNW thin films. Furthermore, the natural oxidation of AgNWs which causes the gradual reduction of the connectivity of the AgNW network is also realized by the THz spectroscopy. The selective oxidation of NW-to-NW junctions weakens the ohmic contact, and for AgNWs near a critical density, it can even lead to metal-insulator transition. The presented results offer invaluable information to accelerate the deployment of metal nanowires for next-generation electronics and optoelectronics on flexible substrates.

  14. Size induced metal-insulator transition in nanostructured niobium thin films: intra-granular and inter-granular contributions

    Energy Technology Data Exchange (ETDEWEB)

    Bose, Sangita [Department of Condensed Matter Physics and Material Science, Tata Institute of Fundamental Research, Mumbai 400005 (India); Banerjee, Rajarshi [Department of Materials Science and Engineering, University of North Texas, Denton, TX 76203 (United States); Genc, Arda [Department of Materials Science and Engineering, Ohio State University, Columbus, OH 43210 (United States); Raychaudhuri, Pratap [Department of Condensed Matter Physics and Material Science, Tata Institute of Fundamental Research, Mumbai 400005 (India); Fraser, Hamish L [Department of Materials Science and Engineering, Ohio State University, Columbus, OH 43210 (United States); Ayyub, Pushan [Department of Condensed Matter Physics and Material Science, Tata Institute of Fundamental Research, Mumbai 400005 (India)

    2006-05-17

    With a reduction in the average grain size in nanostructured films of elemental Nb, we observe a systematic crossover from metallic to weakly insulating behaviour. An analysis of the temperature dependence of the resistivity in the insulating phase clearly indicates the existence of two distinct activation energies corresponding to inter-granular and intra-granular mechanisms of transport. While the high temperature behaviour is dominated by grain boundary scattering of the conduction electrons, the effect of discretization of energy levels due to quantum confinement shows up at low temperatures. We show that the energy barrier at the grain boundary is proportional to the width of the largely disordered inter-granular region, which increases with a decrease in the grain size. For a metal-insulator transition to occur in nano-Nb due to the opening up of an energy gap at the grain boundary, the critical grain size is {approx}8 nm and the corresponding grain boundary width is {approx}1.1 nm.

  15. Metal-insulator transition of valence-controlled VO2 thin film prepared by RF magnetron sputtering using oxygen radical

    Science.gov (United States)

    Suetsugu, Takaaki; Shimazu, Yuichi; Tsuchiya, Takashi; Kobayashi, Masaki; Minohara, Makoto; Sakai, Enju; Horiba, Koji; Kumigashira, Hiroshi; Higuchi, Tohru

    2016-06-01

    We have prepared b-axis-oriented VO2 thin films by RF magnetron sputtering using oxygen radicals as the reactive gas. The VO2 thin films consist of a mixed-valence V3+/V4+ state formed by oxygen vacancies. The V3+ ratio strongly depends on the film thickness and the oxygen partial pressure of the radical gun during deposition. The lattice constant of the b-axis increases and the metal-insulator transition (MIT) temperature decreases with decreasing V3+ ratio, although the VO2 thin films with a high V3+ ratio of 42% do not exhibit MIT. The bandwidths and spectral weights of V 3d a1g and \\text{e}\\text{g}σ bands at around the Fermi level, which correspond to the insulating phase at 300 K, are smaller in the VO2 thin films with a low V3+ ratio. These results indicate that the control of the mixed-valence V3+/V4+ state is important for the MIT of b-axis-oriented VO2 thin films.

  16. Metal-insulator transition in tin doped indium oxide (ITO) thin films: Quantum correction to the electrical conductivity

    Science.gov (United States)

    Kaushik, Deepak Kumar; Kumar, K. Uday; Subrahmanyam, A.

    2017-01-01

    Tin doped indium oxide (ITO) thin films are being used extensively as transparent conductors in several applications. In the present communication, we report the electrical transport in DC magnetron sputtered ITO thin films (prepared at 300 K and subsequently annealed at 673 K in vacuum for 60 minutes) in low temperatures (25-300 K). The low temperature Hall effect and resistivity measurements reveal that the ITO thin films are moderately dis-ordered (kFl˜1; kF is the Fermi wave vector and l is the electron mean free path) and degenerate semiconductors. The transport of charge carriers (electrons) in these disordered ITO thin films takes place via the de-localized states. The disorder effects lead to the well-known `metal-insulator transition' (MIT) which is observed at 110 K in these ITO thin films. The MIT in ITO thin films is explained by the quantum correction to the conductivity (QCC); this approach is based on the inclusion of quantum-mechanical interference effects in Boltzmann's expression of the conductivity of the disordered systems. The insulating behaviour observed in ITO thin films below the MIT temperature is attributed to the combined effect of the weak localization and the electron-electron interactions.

  17. Materials Characterization and Microelectronic Implementation of Metal-insulator Transition Materials and Phase Change Materials

    Science.gov (United States)

    2015-03-26

    Transition MM Metamaterial MO Molecular Orbital MRAM Magnetic Random Access Memory MTFET Mott Transition Field-effect Transistor NA Numerical...including ultra-fast electronic memory, optical switches and filters, and active layers in terahertz metamaterials , among others. The physical mechanisms...modulators, radio frequency (RF) electrical switches, tunable layers on terahertz 3 metamaterials , and high performance bimorph layers for

  18. Disappearance of metal-insulator transition in NdNiO3/LaAlO3 films by ion irradiation controlled stress

    Science.gov (United States)

    Kumar, Yogesh; Choudhary, R. J.; Kumar, Ravi

    2016-09-01

    The effect of strain on the metal-insulator transition (MIT) of the epitaxial NdNiO3 film on the c-axis oriented LaAlO3 single crystal, grown by pulsed laser deposition, has been investigated. Swift heavy ion irradiation was used to vary the strain state of the deposited film. X-ray diffraction confirmed a systematic fluence dependent rise in the in-plane compressive strain, while maintaining the epitaxy of the film. This in-plane compressive strain has been found to reduce the MIT temperature, which finally disappeared for the highest fluence of the irradiation. This is also corroborated with the Raman spectroscopy measurements which suggest that the ion irradiation induced stress is responsible for the suppression of the metal-insulator transition.

  19. Electronic properties and the nature of metal-insulator transition in NdNiO3 prepared at ambient oxygen pressure

    Science.gov (United States)

    Hooda, M. K.; Yadav, C. S.

    2016-06-01

    We report the electronic properties of the NdNiO3, prepared at the ambient oxygen pressure condition. The metal-insulator transition temperature is observed at 192 K, but the low temperature state is found to be less insulating compared to the NdNiO3 prepared at high oxygen pressure. The electric resistivity, Seebeck coefficient and thermal conductivity of the compound show large hysteresis below the metal-insulator transition. The large value of the effective mass (m*~8me) in the metallic state indicates the narrow character of the 3d band. The electric conduction at low temperatures (T=2-20 K) is governed by the variable range hopping of the charge carriers.

  20. The Mott metal-insulator transition in half-filled two-dimensional Hubbard models

    Directory of Open Access Journals (Sweden)

    Peyman Sahebsara

    2008-06-01

    Full Text Available We study the Mott transition in the two dimensional Hubbard model by using the variational cluster approximation. The transition potential obtained is roughly Uc ≈ 2 and 6 for square and triangular lattices, respectively. A comparison between results of this approximation and other quantum cluster methods is presented. Our zero-temperature calculation at strong coupling show that the transition on the triangular and square lattices occur at lower values of compared with other numerical techniques such as DMFT, CDMFT, and DCA. We also study the thermodynamic limit by an extrapolation to infinite size.

  1. Doping driven metal-insulator transitions and charge orderings in the extended Hubbard model

    CERN Document Server

    Kapcia, K J; Capone, M; Amaricci, A

    2016-01-01

    We perform a thorough study of an extended Hubbard model featuring local and nearest-neighbor Coulomb repulsion. Using dynamical mean-field theory we investigated the zero temperature phase-diagram of this model as a function of the chemical doping. The interplay between local and non-local interaction drives a variety of phase-transitions connecting two distinct charge-ordered insulators, i.e., half-filled and quarter-filled, a charge-ordered metal and a Mott insulating phase. We characterize these transitions and the relative stability of the solutions and we show that the two interactions conspire to stabilize the quarter-filled charge ordered phase.

  2. Metal-insulator transition in 3d transition-metal oxides with ABO 3 and A 2BO 4 type structures

    Science.gov (United States)

    Eisaki, H.; Ido, T.; Magoshi, K.; Mochizuki, M.; Yamatsu, H.; Ito, T.; Uchida, S.

    1991-12-01

    3d transition-metal oxides with perovskite and K 2NiF 4 crystal structures, (La,Sr)VO 3, (La,Sr)FeO 3, (La,Sr)CoO 3, LaNiO 3 and (La,Sr) 2NiO 4 systems are investigated focusing on the effect of carrier doping performed by the A-site ion substitution. Both (La,Sr)VO 3 and (La,Sr)CoO 3 systems show an insulator to metal transition by Sr substitution, however, the magnetic behavior differs drastically. The mid-infrared structure induced by Sr substitution is observed in the optical spectra of (La,Sr) 2NiO 4 system. Relation between the behavior of metal-insulator transition and the variation of the electronic and/or spin structure in these systems is discussed in comparison with the high-T c copper oxides.

  3. Metal-insulator phase transition in a VO2 thin film observed with terahertz spectroscopy

    DEFF Research Database (Denmark)

    Jepsen, Peter Uhd; Fischer, Bernd M.; Thoman, Andreas

    2006-01-01

    We investigate the dielectric properties of a thin VO2 film in the terahertz frequency range in the vicinity of the semiconductor-metal phase transition. Phase-sensitive broadband spectroscopy in the frequency region below the phonon bands of VO2 gives insight into the conductive properties...

  4. Mechanisms of spin-flipping and metal-insulator transition in nano-Fe3O4

    Science.gov (United States)

    Dito Fauzi, Angga; Aziz Majidi, Muhammad; Rusydi, Andrivo

    2017-04-01

    Fe3O4 is a half-metallic ferrimagnet with {{T}\\text{C}}∼ 860 K exhibiting metal-insulator transition (MIT) at  ∼120 K. In bulk form, the saturation magnetization is 0.6 Tesla (∼471 emu cm‑3). A recent experimental study has shown that the saturation magnetization of nano-Fe3O4 thin films can achieve up to  ∼760 emu cm‑3, attributed to spin-flipping of Fe ions at tetrahedral sites assisted by oxygen vacancies (V O). Such a system has shown to have higher MIT temperature (∼150 K). The spin-flipping is a new phenomenon in Fe3O4, while the MIT is a long-standing one. Here, we propose a model and calculations to investigate the mechanisms of both phenomena. Our results show that, for the system without V O, the ferrimagnetic configuration is energetically favorable. Remakably, upon inclusion of V O, the ground-state configuration switches into ferromagnetic. As for the MIT, by proposing temperature dependences of some hopping integrals in the model, we demonstrate that the system without and with V O undergo the MIT in slightly different ways, leading to higher MIT temperature for the system with V O, in agreement with the experimental data. Our results also show that the MIT in both systems occur concomitantly with the redistribution of electrons among the three Fe ions in each Fe3O4 formula unit. As such temperature dependences of hopping integrals may arise due to dynamic Jahn–Teller effects, our phenomenological theory may provide a way to reconcile existing theories relating the MIT to the structural transition and the charge ordering.

  5. Quantum transport in 3D Weyl semimetals: Is there a metal-insulator transition?

    Science.gov (United States)

    Ziegler, Klaus

    2016-12-01

    We calculate the transport properties of three-dimensional Weyl fermions in a disordered environment. The resulting conductivity depends only on the Fermi energy and the scattering rate. First we study the conductivity at the spectral node for a fixed scattering rate and obtain a continuous transition from an insulator at weak disorder to a metal at stronger disorder. Within the self-consistent Born approximation the scattering rate depends on the Fermi energy. Then it is crucial that the limits of the conductivity for a vanishing Fermi energy and a vanishing scattering rate do not commute. As a result, there is also metallic behavior in the phase with vanishing scattering rate and only a quantum critical point remains as an insulating phase. The latter turns out to be a critical fixed point in terms of a renormalization-group flow.

  6. Three-dimensional electronic structures and the metal-insulator transition in Ruddlesden-Popper iridates

    Science.gov (United States)

    Yamasaki, A.; Fujiwara, H.; Tachibana, S.; Iwasaki, D.; Higashino, Y.; Yoshimi, C.; Nakagawa, K.; Nakatani, Y.; Yamagami, K.; Aratani, H.; Kirilmaz, O.; Sing, M.; Claessen, R.; Watanabe, H.; Shirakawa, T.; Yunoki, S.; Naitoh, A.; Takase, K.; Matsuno, J.; Takagi, H.; Sekiyama, A.; Saitoh, Y.

    2016-09-01

    In this study, we systematically investigate three-dimensional (3D) momentum (ℏ k )-resolved electronic structures of Ruddlesden-Popper-type iridium oxides Srn +1IrnO3 n +1 using soft-x-ray (SX) angle-resolved photoemission spectroscopy (ARPES). Our results provide direct evidence of an insulator-to-metal transition that occurs upon increasing the dimensionality of the IrO2-plane structure. This transition occurs when the spin-orbit-coupled jeff=1 /2 band changes its behavior in the dispersion relation and moves across the Fermi energy. In addition, an emerging band along the Γ (0,0,0)-R (π ,π ,π ) direction is found to play a crucial role in the metallic characteristics of SrIrO3. By scanning the photon energy over 350 eV, we reveal the 3D Fermi surface in SrIrO3 and kz-dependent oscillations of photoelectron intensity in Sr3Ir2O7 . In contrast to previously reported results obtained using low-energy photons, folded bands derived from lattice distortions and/or magnetic ordering make significantly weak (but finite) contributions to the k -resolved photoemission spectrum. At the first glance, this leads to the ambiguous result that the observed k -space topology is consistent with the unfolded Brillouin zone (BZ) picture derived from a nonrealistic simple square or cubic Ir lattice. Through careful analysis, we determine that a superposition of the folded and unfolded band structures has been observed in the ARPES spectra obtained using photons in both ultraviolet and SX regions. To corroborate the physics deduced using low-energy ARPES studies, we propose to utilize SX-ARPES as a powerful complementary technique, as this method surveys more than one whole BZ and provides a panoramic view of electronic structures.

  7. Tuning the metal-insulator transition in NdNiO3 thin films

    Science.gov (United States)

    Shiyani, T.; Shekhada, K. G.; Savaliya, C. R.; Markna, J. H.

    2017-05-01

    The RNiO3 (R is rare earth) perovskites are famous for their metal to insulator transition (MIT). The temperature can be transformed and depends on the nature of the rare earth. The MIT in thin films and heterostructures of RNiO3 propose the chance to control the MIT as a function of thickness via strain using different substrates. We have reported the electrical transport properties of NdNiO3/NdGaO3, and NNO/NGO/STO structures. These structures were fabricated by pulsed laser deposition (PLD) method. The temperature of the MIT changes from 155K to 195 K. The electrical resistivity of the heterostructures undergoes MIT, depending on the thickness and deposition conditions. Thickness and deposition temperature were found to have a great impact on the electrical transport properties. The shift in TMI changes with thickness and it larger for thinner NdNiO3. The MIT of NNO thin films is responsive to strain and its partial relaxation creates an inhomogeneous strain field that broadens the MIT. This study may be potentially applicable to Mott transistor devices.

  8. The metal-insulator transition of the half integer quantum-Hall effect in epitaxial graphene

    Science.gov (United States)

    Neal, Adam; Shen, Tian; Gu, Jiangjiang; Xu, Min; Bolen, Michael; Capano, Michael; Engel, Lloyd; Ye, Peide

    2010-03-01

    The observation of the half integer quantum-Hall effect (QHE) in Hall resistance along with the pronounced Shubnikov-de Haas (SdH) oscillations confirms that the electrical properties of epitaxial graphene on SiC share the same relativistic physics as those in exfoliated graphene films. The temperature-dependent half-width δB(T) of the SdH peaks and the maximum of the slope of the Hall resistance ρxy/B of gated epitaxial graphene are investigated at temperatures between 0.4 K to 300K. The preliminary data shows δB(T) for the first Laudau level of electrons in epitaxial graphene on SiC (0001) display a power-law behavior with a scaling exponent κ 0.43, being consistent with the previously reported results from 2DES formed at AlGaAs/GaAs or InGaAs/InP heterojunctions [1,2] and the exfoliated graphene [3]. More detailed results on κ for high Laudau levels and the study of size-dependence of the quantum-Hall plateau-plateau transition in epitaxial graphene will also be presented. [1] H.P. Wei, D.C. Tsui, M.A. Paalanen, and A.M.M. Pruisken, Phys. Rev. Lett. 61, 1294 (1988). [2] S. Koch, R.J. Haug, K. von Klitzing, and K. Ploog, Phys. Rev. Lett. 67, 883 (1991). [3] A.J.M. Giesbers, U. Zeitler, L.A. Ponomarenko, R. Yang, K.S. Novoselov, A.K. Geim, and J.C. Maan, arXiv:0908.0461v1.

  9. Charge Mediated Reversible Metal-Insulator Transition in Monolayer MoTe2 and WxMo1-xTe2 Alloy.

    Science.gov (United States)

    Zhang, Chenxi; Kc, Santosh; Nie, Yifan; Liang, Chaoping; Vandenberghe, William G; Longo, Roberto C; Zheng, Yongping; Kong, Fantai; Hong, Suklyun; Wallace, Robert M; Cho, Kyeongjae

    2016-08-23

    Metal-insulator transitions in low-dimensional materials under ambient conditions are rare and worth pursuing due to their intriguing physics and rich device applications. Monolayer MoTe2 and WTe2 are distinguished from other TMDs by the existence of an exceptional semimetallic distorted octahedral structure (T') with a quite small energy difference from the semiconducting H phase. In the process of transition metal alloying, an equal stability point of the H and the T' phase is observed in the formation energy diagram of monolayer WxMo1-xTe2. This thermodynamically driven phase transition enables a controlled synthesis of the desired phase (H or T') of monolayer WxMo1-xTe2 using a growth method such as chemical vapor deposition (CVD) and molecular beam epitaxy (MBE). Furthermore, charge mediation, as a more feasible method, is found to make the T' phase more stable than the H phase and induce a phase transition from the H phase (semiconducting) to the T' phase (semimetallic) in monolayer WxMo1-xTe2 alloy. This suggests that a dynamic metal-insulator phase transition can be induced, which can be exploited for rich phase transition applications in two-dimensional nanoelectronics.

  10. Orbital magnetic field driven metal-insulator transition in spinless extended Falicov-Kimball model on a triangular lattice

    Science.gov (United States)

    Yadav, Umesh K.

    2017-01-01

    Ground state properties of spinless, extended Falicov-Kimball model (FKM) on a finite size triangular lattice with orbital magnetic field normal to the lattice are studied using numerical diagonalization and Monte-Carlo simulation methods. We show that the ground state configurations of localized electrons strongly depend on the magnetic field. Magnetic field induces a metal to insulator transition accompanied by segregated phase to an ordered regular phase except at density nf = 1 / 2 of localized electrons. It is proposed that magnetic field can be used as a new tool to produce segregated phase which was otherwise accessible only either with correlated hopping or with large on-site interactions.

  11. First-principles study of Sr2Ir1-xRhxO4: charge transfer, spin-orbit coupling change, and the metal-insulator transition

    Science.gov (United States)

    Sim, Jae-Hoon; Kim, Heung-Sik; Han, Myung Joon

    2015-03-01

    Using first-principles density functional theory (DFT) calculations, we investigated the electronic structure of Rh-doped iridate, Sr2Ir1-xRhxO4 for which the doping (x) dependent metal-insulator transition (MIT) has been reported experimentally and the controversial discussion developed regarding the origin of this transition. Our DFT+U calculation shows that the value of remains largely intact over the entire doping range considered here (x = 0 . 0 , 0 . 125 , 0 . 25 , 0 . 50 , 0 . 75 , and 1 . 0) in good agreement with the branching ratio measured by x-ray absorption spectroscopy. Also contrary to a previous picture to explain MIT based on the charge transfer between the transition-metal sites, our calculation clearly shows that those sites remain basically isoelectronic while the impurity bands of predominantly rhodium character are introduced near the Fermi level. As the doping increases, this impurity band overlaps with lower Hubbard band of iridium, leading to metal-insulator transition. The results will be discussed with comparison to the case of Ru doping. Computational resources were suported by The National Institute of Supercomputing and Networking/Korea Institute of Science and Technology Information with supercomputing resources including technical spport (Grant No. KSC-2013-C2-23).

  12. Dynamically Babinet-invertible metasurface: a capacitive-inductive reconfigurable filter for terahertz waves using vanadium-dioxide metal-insulator transition

    CERN Document Server

    Urade, Yoshiro; Okimura, Kunio; Nakanishi, Toshihiro; Miyamaru, Fumiaki; Takeda, Mitsuo W; Kitano, Masao

    2016-01-01

    This paper proposes a reconfigurable planar metamaterial that can be switched between capacitive and inductive responses using local changes in the electrical conductivity of its constituent material. The proposed device is based on Babinet's principle and exploits the singular electromagnetic responses of metallic checkerboard structures, which are dependent on the local electrical conductivity. Utilizing the heating-induced metal-insulator transition of vanadium dioxide ($\\mathrm{VO}_2$), the proposed metamaterial is designed to compensate for the effect of the substrate and is experimentally characterized in the terahertz regime. This reconfigurable metamaterial can be utilized as a switchable filter and as a switchable phase shifter for terahertz waves.

  13. Field-induced stacking transition of biofunctionalized trilayer graphene

    Energy Technology Data Exchange (ETDEWEB)

    Masato Nakano, C. [Flintridge Preparatory School, La Canada, California 91011 (United States); Sajib, Md Symon Jahan; Samieegohar, Mohammadreza; Wei, Tao [Dan F. Smith Department of Chemical Engineering, Lamar University, Beaumont, Texas 77710 (United States)

    2016-02-01

    Trilayer graphene (TLG) is attracting a lot of attention as their stacking structures (i.e., rhombohedral vs. Bernal) drastically affect electronic and optical properties. Based on full-atom molecular dynamics simulations, we here predict electric field-induced rhombohedral-to-Bernal transition of TLG tethered with proteins. Furthermore, our simulations show that protein's electrophoretic mobility and diffusivity are enhanced on TLG surface. This phenomenon of controllable TLG stacking transition will contribute to various applications including biosensing.

  14. Role of long range Coulomb interaction near the disorder driven metal-insulator transition in Ga1-xMnxAs

    Science.gov (United States)

    Mahmoudian, S.; Miranda, E.; Dobrosavljevic, V.

    2013-03-01

    Surprising signatures of interaction effects on disorder-driven localization have recently been observed by scanning tunneling microscopy of Ga1-xMnxAs, where visualizing the electronic wave function near the metal-insulator transition revealed[1] a pronounced suppression of the local tunneling density of states (LDOS) and enhanced localization only near the Fermi energy. These features highlight the limitation of the non-interacting picture, and point to the crucial importance of the long-range Coulomb interaction. Here, we implement a theoretical approach based on the recently developed Typical-Medium Theory,[2] the conceptually simplest approach to interaction-localization. We show that the presence of long-range Coulomb interaction leads to the simultaneous opening of a soft pseudogap in both the typical (geometrically averaged) and the average (algebraically averaged) LDOS, as the transition is approached. This result is consistent with the experimentally observed features of the STM spectra, suggesting new experiments that should be performed to fully characterize the quantum critical behavior at the metal-insulator transition

  15. Ground-state oxygen holes and the metal-insulator transition in the negative charge-transfer rare-earth nickelates

    Science.gov (United States)

    Bisogni, Valentina; Catalano, Sara; Green, Robert J.; Gibert, Marta; Scherwitzl, Raoul; Huang, Yaobo; Strocov, Vladimir N.; Zubko, Pavlo; Balandeh, Shadi; Triscone, Jean-Marc; Sawatzky, George; Schmitt, Thorsten

    2016-10-01

    The metal-insulator transition and the intriguing physical properties of rare-earth perovskite nickelates have attracted considerable attention in recent years. Nonetheless, a complete understanding of these materials remains elusive. Here we combine X-ray absorption and resonant inelastic X-ray scattering (RIXS) spectroscopies to resolve important aspects of the complex electronic structure of rare-earth nickelates, taking NdNiO3 thin film as representative example. The unusual coexistence of bound and continuum excitations observed in the RIXS spectra provides strong evidence for abundant oxygen holes in the ground state of these materials. Using cluster calculations and Anderson impurity model interpretation, we show that distinct spectral signatures arise from a Ni 3d8 configuration along with holes in the oxygen 2p valence band, confirming suggestions that these materials do not obey a conventional positive charge-transfer picture, but instead exhibit a negative charge-transfer energy in line with recent models interpreting the metal-insulator transition in terms of bond disproportionation.

  16. Voltage control of metal-insulator transition and non-volatile ferroelastic switching of resistance in VOx/PMN-PT heterostructures.

    Science.gov (United States)

    Nan, Tianxiang; Liu, Ming; Ren, Wei; Ye, Zuo-Guang; Sun, Nian X

    2014-08-04

    The central challenge in realizing electronics based on strongly correlated electronic states, or 'Mottronics', lies in finding an energy efficient way to switch between the distinct collective phases with a control voltage in a reversible and reproducible manner. In this work, we demonstrate that a voltage-impulse-induced ferroelastic domain switching in the (011)-oriented 0.71Pb(Mg1/3Nb2/3)O3-0.29PbTiO3 (PMN-PT) substrates allows a robust non-volatile tuning of the metal-insulator transition in the VOx films deposited onto them. In such a VOx/PMN-PT heterostructure, the unique two-step electric polarization switching covers up to 90% of the entire poled area and contributes to a homogeneous in-plane anisotropic biaxial strain, which, in turn, enables the lattice changes and results in the suppression of metal-insulator transition in the mechanically coupled VOx films by 6 K with a resistance change up to 40% over a broad range of temperature. These findings provide a framework for realizing in situ and non-volatile tuning of strain-sensitive order parameters in strongly correlated materials, and demonstrate great potentials in delivering reconfigurable, compactable, and energy-efficient electronic devices.

  17. Pressure effect on the superconductivity and the metal-insulator transition in Cu sub 1 sub sub - sub x Zn sub x Ir sub 2 S sub 4

    CERN Document Server

    Cao, G; Kitazawa, H; Isobe, M; Matsumoto, T

    2002-01-01

    The variations of the superconducting transition temperature T sub c and the metal-insulator (MI) transition temperature T sub M sub I were investigated as a function of pressure in the superconducting Cu sub 1 sub sub - sub x Zn sub x Ir sub 2 S sub 4 (0.3 <= x <= 0.5) system. The experiment was performed by measuring the temperature dependence of resistance under the pressures up to 1.5 GPa. It is shown that the external pressure destroys the superconductivity, and gives rise to the MI transitions. The result is discussed in terms of the stabilization of the insulating phase at high pressures and the phase separation associated with the charge segregation. It is proposed that the BCS Cooper pairs compete with the proposed bipolarons under certain pressures.

  18. Changes in the electronic structure and spin dynamics across the metal-insulator transition in La1 -xSrxCoO3

    Science.gov (United States)

    Smith, R. X.; Hoch, M. J. R.; Moulton, W. G.; Kuhns, P. L.; Reyes, A. P.; Boebinger, G. S.; Zheng, H.; Mitchell, J. F.

    2016-01-01

    The magnetoelectronic properties of La1 -xSrxCoO3 , which include giant magnetoresistance, are strongly dependent on the level of hole doping. The system evolves, with increasing x , from a spin glass insulator to a metallic ferromagnet with a metal-insulator (MI) transition at xC ˜0.18 . Nanoscale phase separation occurs in the insulating phase and persists, to some extent, into the just-metallic phase. The present experiments at 4.2 K have used 139139 La nuclear magnetic resonance to investigate the transition from hopping dynamics for x xC to Korringa-like ferromagnetic metal behavior for x > xC. A marked decrease in the spin-lattice relaxation rate is found in the vicinity of xC as the MI transition is crossed. This behavior is accounted for in terms of the evolution of the electronic structure and dynamics with cluster size.

  19. Substrate-induced microstructure effects on the dynamics of the photo-induced Metal-insulator transition in VO$_2$ thin films

    CERN Document Server

    Radue, E; Kittiwatanakul, S; Lu, J; Wolf, S A; Rossi, E; Lukaszew, R A; Novikova, I

    2014-01-01

    We investigate the differences in the dynamics of the ultrafast photo-induced metal-insulator transition (MIT) of two VO$_2$ thin films deposited on different substrates, TiO$_2$ and Al$_2$O$_3$, and in particular the temperature dependence of the threshold laser fluence values required to induce various MIT stages in a wide range of sample temperatures (150 K - 320 K). We identified that, although the general pattern of MIT evolution was similar for the two samples, there were several differences. Most notably, the threshold values of laser fluence required to reach the transition to a fully metallic phase in the VO$_2$ film on the TiO$_2$ substrate were nearly constant in the range of temperatures considered, whereas the VO$_2$/Al$_2$O$_3$ sample showed clear temperature dependence. Our analysis qualitatively connects such behavior to the structural differences in the two VO$_2$ films.

  20. Hopping energy and percolation-type transport in p-GaAs low densities near the 2D metal-insulator transition at zero magnetic field

    Science.gov (United States)

    Dlimi, S.; El kaaouachi, A.; Narjis, A.; Limouny, L.; Sybous, A.; Errai, M.

    2013-10-01

    We investigated the temperature dependence of resistivity of a high mobility two-dimensional holes system grown on the (311) GaAs surface in the absence of the magnetic field near the metal-insulator transition. The Coulomb hopping was found in a wide range of temperature and carrier density. Quantitative analysis of our results suggests that a crossover from Efros-Shklovskii to Mott variable range hopping due to screening phenomenon when the hopping distance increases. We found that using the 2D single particle hopping amplitude CES gives unreasonably high localization lengths. Therefore, we believe that electrical transport is dominated by correlated hopping and the hopping amplitude must be renormalized by a reduction factor A≈1.6. The localization length appears to diverge in a power-law fashion near the transition point. The analysis of the hopping gives results consistent with the prediction of the critical point from a recent study of percolation and other experiences.

  1. Effects of low-energy excitations on spectral properties at higher binding energy: the metal-insulator transition of VO(2).

    Science.gov (United States)

    Gatti, Matteo; Panaccione, Giancarlo; Reining, Lucia

    2015-03-20

    The effects of electron interaction on spectral properties can be understood in terms of coupling between excitations. In transition-metal oxides, the spectral function close to the Fermi level and low-energy excitations between d states have attracted particular attention. In this work we focus on photoemission spectra of vanadium dioxide over a wide (10 eV) range of binding energies. We show that there are clear signatures of the metal-insulator transition over the whole range due to a cross coupling of the delocalized s and p states with low-energy excitations between the localized d states. This coupling can be understood by advanced calculations based on many-body perturbation theory in the GW approximation. We also advocate the fact that tuning the photon energy up to the hard-x-ray range can help to distinguish fingerprints of correlation from pure band-structure effects.

  2. Thickness-Induced Metal-Insulator Transition in Sb-doped SnO2 Ultrathin Films: The Role of Quantum Confinement.

    Science.gov (United States)

    Ke, Chang; Zhu, Weiguang; Zhang, Zheng; Tok, Eng Soon; Ling, Bo; Pan, Jisheng

    2015-11-30

    A thickness induced metal-insulator transition (MIT) was firstly observed in Sb-doped SnO2 (SnO2:Sb) epitaxial ultrathin films deposited on sapphire substrates by pulsed laser deposition. Both electrical and spectroscopic studies provide clear evidence of a critical thickness for the metallic conductivity in SnO2:Sb thin films and the oxidation state transition of the impurity element Sb. With the shrinkage of film thickness, the broadening of the energy band gap as well as the enhancement of the impurity activation energy was studied and attributed to the quantum confinement effect. Based on the scenario of impurity level pinning and band gap broadening in quantum confined nanostructures, we proposed a generalized energy diagram to understand the thickness induced MIT in the SnO2:Sb system.

  3. Tuning the metal-insulator transition via epitaxial strain and Co doping in NdNiO3 thin films grown by polymer-assisted deposition

    Science.gov (United States)

    Yao, Dan; Shi, Lei; Zhou, Shiming; Liu, Haifeng; Zhao, Jiyin; Li, Yang; Wang, Yang

    2016-01-01

    The epitaxial NdNi1-xCoxO3 (0 ≤ x ≤ 0.10) thin films on (001) LaAlO3 and (001) SrTiO3 substrates were grown by a simple polymer-assisted deposition technique. The co-function of the epitaxial strain and Co doping on the metal-insulator transition in perovskite nickelate NdNiO3 thin films is investigated. X-ray diffraction and scanning electron microscopy reveal that the as-prepared thin films exhibit good crystallinity and heteroepitaxy. The temperature dependent resistivities of the thin films indicate that both the epitaxial strain and Co doping lower the metal-insulator (MI) transition temperature, which can be treated as a way to tune the MI transition. Furthermore, under the investigated Co-doping levels, the MI transition temperature (TMI) shifts to low temperatures with Co content increasing under both compressive and tensile strain, and the more distinction is in the former situation. When x is increased up to 0.10, the insulating phase is completely suppressed under the compressive strain. With the strain increases from compression to tension, the resistivities are enhanced both in the metal and insulating regions. However, the Co-doping effect on the resistivity shows a more complex situation. As Co content x increases from zero to 0.10, the resistivities are reduced both in the metal and insulating regions under the tensile strain, whereas they are enhanced in the high-temperature metal region under the compressive strain. Based on the temperature dependent resistivity in the metal regions, it is suggested that the electron-phonon coupling in the films becomes weaker with the increase of both the strain and Co-doping.

  4. Tuning the metal-insulator transition via epitaxial strain and Co doping in NdNiO{sub 3} thin films grown by polymer-assisted deposition

    Energy Technology Data Exchange (ETDEWEB)

    Yao, Dan; Shi, Lei, E-mail: shil@ustc.edu.cn; Zhou, Shiming; Liu, Haifeng; Zhao, Jiyin; Li, Yang [Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei, Anhui 230026 (China); Wang, Yang [Instrumental Analysis Center, Hefei University of Technology, Hefei, Anhui 230009 (China)

    2016-01-21

    The epitaxial NdNi{sub 1-x}Co{sub x}O{sub 3} (0 ≤ x ≤ 0.10) thin films on (001) LaAlO{sub 3} and (001) SrTiO{sub 3} substrates were grown by a simple polymer-assisted deposition technique. The co-function of the epitaxial strain and Co doping on the metal-insulator transition in perovskite nickelate NdNiO{sub 3} thin films is investigated. X-ray diffraction and scanning electron microscopy reveal that the as-prepared thin films exhibit good crystallinity and heteroepitaxy. The temperature dependent resistivities of the thin films indicate that both the epitaxial strain and Co doping lower the metal-insulator (MI) transition temperature, which can be treated as a way to tune the MI transition. Furthermore, under the investigated Co-doping levels, the MI transition temperature (T{sub MI}) shifts to low temperatures with Co content increasing under both compressive and tensile strain, and the more distinction is in the former situation. When x is increased up to 0.10, the insulating phase is completely suppressed under the compressive strain. With the strain increases from compression to tension, the resistivities are enhanced both in the metal and insulating regions. However, the Co-doping effect on the resistivity shows a more complex situation. As Co content x increases from zero to 0.10, the resistivities are reduced both in the metal and insulating regions under the tensile strain, whereas they are enhanced in the high-temperature metal region under the compressive strain. Based on the temperature dependent resistivity in the metal regions, it is suggested that the electron-phonon coupling in the films becomes weaker with the increase of both the strain and Co-doping.

  5. DC current induced metal-insulator transition in epitaxial Sm0.6Nd0.4NiO3/LaAlO3 thin film

    Directory of Open Access Journals (Sweden)

    Haoliang Huang

    2014-05-01

    Full Text Available The metal-insulator transition (MIT in strong correlated electron materials can be induced by external perturbation in forms of thermal, electrical, optical, or magnetic fields. We report on the DC current induced MIT in epitaxial Sm0.6Nd0.4NiO3 (SNNO thin film deposited by pulsed laser deposition on (001-LaAlO3 substrate. It was found that the MIT in SNNO film not only can be triggered by thermal, but also can be induced by DC current. The TMI of SNNO film decreases from 282 K to 200 K with the DC current density increasing from 0.003 × 109 A•m−2 to 4.9 × 109 A•m−2. Based on the resistivity curves measured at different temperatures, the MIT phase diagram has been successfully constructed.

  6. Pressure-induced metal-insulator transition and absence of magnetic order in FeGa3 from a first-principles study

    Science.gov (United States)

    Osorio-Guillén, J. M.; Larrauri-Pizarro, Y. D.; Dalpian, G. M.

    2012-12-01

    The intermetallic compound FeGa3 is a narrow-gap semiconductor with a measured gap between 0.2 and 0.6 eV. The presence of iron d states on the top of the valence band and on the bottom of the conduction band, together with its moderate electronic correlation (U/W˜0.6), have led to the question of whether there is magnetic order in this compound. We have examined the possible presence of magnetism in FeGa3 as well as its electronic structure at high pressures, using the density functional theory (DFT) + U method with the intermediated double-counting scheme. We have found that for an optimized value of the Yukawa screening length λ, there is no magnetic moment on the iron ions (μ=0), implying that FeGa3 is nonmagnetic. We have also found that around a pressure of 25 GPa a metal-insulator transition takes place.

  7. Isotope effect on metal-insulator transition of (EDO-TTF) 2XF 6 (X = P, As) with multi-instability of metallic state

    Science.gov (United States)

    Nakano, Yoshiaki; Balodis, Karlis; Yamochi, Hideki; Saito, Gunzi; Uruichi, Mikio; Yakushi, Kyuya

    2008-12-01

    The partially deuterated 4,5-ethylenedioxy-tetrathiafulvalene- d2 (EDO-TTF- d2) was synthesized from the undeuterated EDO-TTF- d0. The single crystals of (EDO-TTF- d2) 2XF 6 (X = P, As) were prepared by the conventional electrocrystallization technique. The deuterium contents of EDO-TTF- d2 itself and the radical cation salts were 99% D by mass spectral analysis. The magnetic susceptibility measurement revealed that (EDO-TTF- d2) 2XF 6 undergoes a metal-insulator transition at 2-3 K higher temperature than the undeuterated salts. In infrared and Raman spectra, significant isotope shifts were observed not only on C-H vibrational modes but also on TTF-skeletal modes. The assignment of experimental bands was performed on the basis of normal-mode analysis at B3LYP/6-31G(d,p) level of theory.

  8. X-ray absorption and photoemission study of spin state and metal-insulator transition in GdBaCo{sub 2}O{sub 5.47}

    Energy Technology Data Exchange (ETDEWEB)

    Hu, Z.; Wu Hua; Koethe, T.; Haverkort, M.W.; Burnus, T.; Gegner, J.; Zobel, C.; Lorenz, T.; Tjeng, L.H. [2. Physikalisches Inst., Univ. zu Koeln (Germany); Barilo, S.N. [Inst. of Solid State and Semiconductors Physics, National Academy of Sciences (Belarus); Lin, H.J.; Chen, C.T. [National Synchrotron Radiation Research Center, Tsinchu (China); Brookes, N.B. [European Synchrotron Radiation Facility (France)

    2007-07-01

    The fundamental physics of the magnetoresistance materials RBaCo{sub 2}O{sub 5.5} (R=Sm,Eu,Gd,Tb,Dy,Y), particularly the issue of spin-state and metal-insulator transition (MIT), is currently under intense debate. Using valence-baud photoemission spectra and X-ray absorption spectra at both the O-K and Co-L{sub 2,3} edges, we found that crossing the MIT, the band gap decreases but does not collapse across the MIT. More significantly, our spectroscopic evidence firmly rules out the widely accepted model for the low-temperate phase, namely that the Co{sup 3+} ions in the octahedral sites are mainly low spin and in the pyramidal sites intermediate spin. We rather found that the MIT in this system is very similar to the high temperature (600 K) MIT of LaCoO{sub 3}. (orig.)

  9. Interlayer coupling and the metal-insulator transition in Pr-substituted Bi2Sr2CaCu2O8+y

    Science.gov (United States)

    Quitmann, C.; Beschoten, B.; Kelley, R. J.; Güntherodt, G.; Onellion, M.

    1995-05-01

    Substitution of rare-earth ions for Ca in Bi2Sr2CaCu2O8+y is known to cause a metal-insulator transition. Using resonant photoemission we study how this chemical substitution affects the electronic structure of the material. For the partial Cu density of states at EF and in the region of the valence band we observe no significant difference between a pure superconducting and an insulating sample with 60% Pr for Ca substitution. This suggests that the states responsible for superconducting are predominantly O states. The Pr 4f partial density of states was extracted utilizing the super-Coster-Kronig Pr 4d-4f resonance. It consists of a single peak at 1.36 eV binding energy. The peak shows a strongly asymmetric Doniach-Šunjic line shape indicating the presence of a band of electronic states with a cutoff at EF even in this insulating sample. This finding excludes a band gap in the insulating sample and supports the existence of a mobility gap caused by spatial localization of the carriers. The presence of such carriers at the Pr site between the CuO2 planes shows that the electronic structure is not purely two dimensional but that there is finite interlayer coupling. The resonance enhancement of the photoemission cross section at the Pr 4d threshold was studied for the Pr 4f and for Cu states. Both the Pr 4f and the Cu states show a Fano-like resonance. This resonance of Cu states with Pr states is another indication of coupling between the Pr states and those in the CuO2 plane. Because of the statistical distribution of the Pr ions this coupling leads to a nonperiodic potential for the states in the CuO2 planes which can lead to localization and thus to the observed metal-insulator transition.

  10. In-Si(111)(4 x 1)/(8 x 2) nanowires: Electron transport, entropy, and metal-insulator transition

    Energy Technology Data Exchange (ETDEWEB)

    Schmidt, W.G.; Sanna, S.; Babilon, M.; Vollmers, N.J.; Gerstmann, U. [Lehrstuhl fuer Theoretische Physik, Universitaet Paderborn (Germany); Wippermann, S. [Department of Chemistry, University of California, Davis (United States)

    2012-02-15

    In this paper the recent experimental and theoretical progress in understanding the properties of the In-Si(111)(4 x 1)/(8 x 2) nanowire array - a prototypical model system for exploring electron transport at the atomic scale - is reviewed. Density functional theory (DFT) calculations illustrate how strongly structural, vibrational, and electronic properties of atomic-scale wires are intertwined. Numerical simulations of the nanowire optical response in comparison with recent measurements settle eventually the long-standing debate on the nanowire ground-state geometry in favor of hexagons. Soft phonon modes are found to transform the nanowire structurally between the insulating hexagon structure and metallic In zigzag chains. The subtle balance between the lower energy of the insulating phase and the larger vibrational entropy of the metallic wires is demonstrated to cause the temperature-dependent phase transition. The dynamic fluctuation model proposed earlier to explain the phase transition is shown to contradict the experimental information on the metal insulator transition of the nanowires. The influence of adatoms on the quantum transport and phase transition is discussed. Schematic drawing of the main structural motifs of the In-induced Si(111)(8 x 2) and (4 x 1) reconstructions, In hexagons and zigzag chains, respectively. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  11. Field induced phase transition in the few photon regime

    CERN Document Server

    Panferov, A D; Titov, A I; Kaempfer, B; Otto, A; Blaschke, D B; Juchnowski, L

    2016-01-01

    Some features of the field induced phase transition accompanied by the vacuum creation of an electron-positron plasma (EPP) in strong time-dependent electric fields have been discussed in the work [1] in the domain of the tunneling mechanism ($\\omega \\ll m$, where $\\omega$ is the characteristic frequency of the external field and $m$ is the electron mass). In the present contribution the features of the this process will be considered in the few photon domain where $\\omega \\sim m$. We observe a narrowing of the transient domain of the fast oscillations and, mainly, a considerable growth of the effectiveness of the EPP production. Under these circumstances, we see an increase of the effectiveness of the EPP creation in the particular case of a bifrequent excitation, where both mechanisms (tunneling and few photon) act simultaneously [2,3].

  12. Localization-driven metal-insulator transition in epitaxial hole-doped Nd1-x Sr x NiO3 ultrathin films

    Science.gov (United States)

    Wang, Le; Chang, Lei; Yin, Xinmao; Rusydi, Andrivo; You, Lu; Zhou, Yang; Fang, Liang; Wang, Junling

    2017-01-01

    Advances in thin film growth technologies make it possible to obtain ultra-thin perovskite oxide films and open the window for controlling novel electronic phases for use in functional nanoscale electronics, such as switches and sensors. Here, we study the thickness-dependent transport characteristics of high-quality ultrathin Nd0.9Sr0.1NiO3 (Sr-NNO) films, which were grown on LaAlO3 (0 0 1) single-crystal substrates by using pulsed laser deposition method. Thick Sr-NNO films (25 unit cells) exhibit metallic behavior with the electrical resistivity following the T  n (n  system, while a temperature driven metal-insulator transition (MIT) is observed with films of less than 15 unit cells. The transition temperature increases with reducing film thickness, until the insulating characteristic is observed even at room temperature. The emergence of the insulator ground state can be attributed to weak localization driven MIT expected by considering Mott-Ioffe-Regel limit. Furthermore, the magneto-transport study of Sr-NNO ultrathin films also confirms that the observed MIT is due to the disorder-induced localization rather than the electron-electron interactions.

  13. Pressure dependence of the metal-insulator transition in κ-(BEDT-TTF)2Hg(SCN)2Cl: optical and transport studies

    Science.gov (United States)

    Löhle, A.; Rose, E.; Singh, S.; Beyer, R.; Tafra, E.; Ivek, T.; Zhilyaeva, E. I.; Lyubovskaya, R. N.; Dressel, M.

    2017-02-01

    The two-dimensional organic conductor κ-(BEDT-TTF)2-Hg(SCN)2Cl exhibits a pronounced metal-insulator transition at {{T}\\text{CO}}=30 K. From the splitting of the molecular vibrations, the phase transition can be unambiguously assigned to charge-ordering with 2{δρ}=0.2e . We have investigated the pressure evolution of this behavior by temperature-dependent electrical transport measurements and optical investigations applying hydrostatic pressure up to 12 kbar. The data reveal a mean-field like down-shift of {{T}\\text{CO}}≤ft( p\\right) with a critical pressure of {{p}c}=0.7+/- 0.1 kbar and a metallic state above the suppression of the charge-ordered state; no traces of superconductivity could be identified down to T  =  1.5 K. As the charge order {δρ} sets in abruptly with decreasing temperature, its size remains unaffected by pressure. However, the fraction of charge imbalanced molecules decreases until it is completely absent above 1.6 kbar.

  14. Hopping conduction in p-type MoS{sub 2} near the critical regime of the metal-insulator transition

    Energy Technology Data Exchange (ETDEWEB)

    Park, Tae-Eon; Jang, Chaun, E-mail: cujang@kist.re.kr, E-mail: presto@kist.re.kr [Center for Spintronics, Korea Institute of Science and Technology, Seoul 136-791 (Korea, Republic of); Suh, Joonki; Wu, Junqiao [Department of Materials Science and Engineering, University of California, Berkeley, California 94720 (United States); Seo, Dongjea [Center for Spintronics, Korea Institute of Science and Technology, Seoul 136-791 (Korea, Republic of); Department of Materials Science and Engineering, Yonsei University, Seoul 120-749 (Korea, Republic of); Park, Joonsuk [Department of Materials Science and Engineering, Stanford University, Stanford, California 94305 (United States); Lin, Der-Yuh [Department of Electronics Engineering, National Changhua University of Education, Changhua 50007, Taiwan (China); Huang, Ying-Sheng [Department of Electronics Engineering, National Taiwan University of Science and Technology, Taipei 10607, Taiwan (China); Choi, Heon-Jin [Department of Materials Science and Engineering, Yonsei University, Seoul 120-749 (Korea, Republic of); Chang, Joonyeon, E-mail: cujang@kist.re.kr, E-mail: presto@kist.re.kr [Center for Spintronics, Korea Institute of Science and Technology, Seoul 136-791 (Korea, Republic of); Department of Nanomaterials Science and Engineering, Korea University of Science and Technology, Daejeon 305-350 (Korea, Republic of)

    2015-11-30

    We report on temperature-dependent charge and magneto transport of chemically doped MoS{sub 2}, p-type molybdenum disulfide degenerately doped with niobium (MoS{sub 2}:Nb). The temperature dependence of the electrical resistivity is characterized by a power law, ρ(T) ∼ T{sup −0.25}, which indicates that the system resides within the critical regime of the metal-insulator (M-I) transition. By applying high magnetic field (∼7 T), we observed a 20% increase in the resistivity at 2 K. The positive magnetoresistance shows that charge transport in this system is governed by the Mott-like three-dimensional variable range hopping (VRH) at low temperatures. According to relationship between magnetic-field and temperature dependencies of VRH resistivity, we extracted a characteristic localization length of 19.8 nm for MoS{sub 2}:Nb on the insulating side of the M-I transition.

  15. Controlling the sharpness of room-temperature metal-insulator transition in epitaxial Sm0.5Nd0.5NiO3 films

    Directory of Open Access Journals (Sweden)

    X. K. Lian

    2013-06-01

    Full Text Available Sm0.5Nd0.5NiO3 (SNNO films with metal-insulator transition (MIT at room-temperature (∼300 K have been grown on NdGaO3 (001 substrates by pulsed laser deposition. By modifying the parameters of oxygen pressure, substrate temperature, and film thickness, the role of oxygen vacancies and strain relaxation on the MIT of SNNO films was systematically analyzed. The strain status of the films was carefully characterized by means of high resolution x-ray diffraction. The results revealed that for the fully strained films (≤20 nm an increment of deposition oxygen pressure (and/or temperature would decrease the content of oxygen vacancies and Ni2+ in the films, leading to a sharp MIT. In contrast, the strain relaxation occurs in the thicker films (>20 nm despite an optimized oxygen pressure (temperature was adapted for the deposition, which results in an inferior transport property and surface morphology. Specifically, a broadening MIT and a doublet TMI was observed in the partially strained films, where one TMI kept a stable value around 300 K in analogues to that of fully strained film, and another one increased with the increment of the film thickness, reaching a highest value of 330 K. This might be induced by the coexistence of a fully strained part and a strain-relaxed portion in the thicker films that observed on high resolution X-ray reciprocal space mappings.

  16. Conductance Modulation across the Metal-Insulator Transition in Single Nanowire Devices of doped-VO2 Gated with Ionic Liquid

    Science.gov (United States)

    Stabile, Adam; Whittaker, Luisa; Banerjee, Sarbajit; Sambandamurthy, G.

    2013-03-01

    Studies of the effects of charge modulation in VO2 systems may provide useful insights into the microscopic mechanisms behind its metal-insulator transition (MIT). Recently, ionic liquid (IL) has become a popular material for gating nanodevices due to its superior charge accumulation capabilities. Thus, using IL to gate single nanowires of W-doped-VO2, we systematically study the modulation of electrical transport across the temperature-driven and voltage-driven MIT as a function of gate voltage. We report the manifestation of hysteresis loops, which show an unprecedented modulation of resistance and current by as large as 20%. Moreover, we show that the largest modulation loop coincides with the largest changes in resistance across the temperature-driven MIT suggesting that the memory behavior in VO2 and its MIT are closely linked. Similar behavior is also observed across the voltage-driven MIT. These studies lay the ground work for an alternative approach to understanding the mechanisms behind the MIT in VO2 systems when driven by different external parameters.

  17. Metal-insulator transition in Si{sub 0.7}Ge{sub 0.3} disordered by fast neutron radiation

    Energy Technology Data Exchange (ETDEWEB)

    Zhidkov, A.V. [AN Ukrainskoj SSR, Kiev (Ukraine). Inst. Yadernykh Issledovanij

    1996-10-01

    Both n- and p-type heavily doped and irradiated Si{sub 0.7}Ge{sub 0.3} (N{sub D}, N{sub A}{approx}2.10{sup 26} cm{sup -3}) alloys behaviour was experimentally studied. After irradiation in vertical channels of Kiev WWR-M research reactor with neutron fluence of 10{sup 25} neutron/m{sup 2} (E>1 MeV), the material was determined to be an insulator because of observed Anderson-type metal-insulator transition. There were temperature dependency of specific resistance and Hall effect measurements, which allowed distinct detection of both the {epsilon}{sub 1}-conductivity provided by the thermal activation of carriers from Fermi level to percolation threshold and {epsilon}{sub 3}, where the hopping mechanism dominates. The unusual parameters of hopping process were observed at T<200 K, where this process dominates. The Fermi level value was estimated to be 55 meV relative to the mobility edge; estimated electron state localization radius value is <10 A. (orig.).

  18. Nanoscale control of the LaAlO3/SrTiO3 metal-insulator transition using a self-assembled monolayer of APTES

    Science.gov (United States)

    Li, Jianan; Huang, Mengcheng; Irvin, Patrick; Levy, Jeremy; Ryu, Sangwoo; Eom, Chang-Beom; Eichelsdoerfer, Daniel; Brown, Keith; Mirkin, Chad

    2014-03-01

    Nanoscale control over the metal-insulator transition at oxide interfaces represents an exciting opportunity for science and technology. Nanostructures created from 3-unit-cell LaAlO3/SrTiO3 heterostructures via a conductive AFM technique typically decay within hours under ambient conditions, representing a challenge for some technologies. By chemically modifying the top LaAlO3 surface with a self-assembled monolayer of (3-Aminopropyl)triethoxysilane (APTES), normally conductive 4-unit-cell LaAlO3/SrTiO3 can be made highly insulating. The APTES layer can be locally patterned, revealing a highly stable conductive nanoregion. Four-terminal measurements show that nanowires created by selective desorption of APTES remain conductive indefinitely under ambient conditions. The results suggest a robust mechanism for creating long-lived nanostructures at oxide interfaces. We gratefully acknowledge support from NSF (DMR-1124131) and AFOSR (FA9550-12-1-0268, FA9550-10-1-0524, FA9550-12-1-0342).

  19. Synthetic beta-K(0.33)V2O5 nanorods: a metal-insulator transition in vanadium oxide bronze.

    Science.gov (United States)

    Zhang, Xiaodong; Yan, Wensheng; Xie, Yi

    2011-12-02

    We found a linear relationship between the metal-insulator transition (MIT) temperature and the A(+) ionic radius of the beta-A(0.33)V(2)O(5) bronze family, leading our attention to beta-K(0.33)V(2)O(5) which has been neglected for a long time. We have introduced a facile hydrothermal method to obtain the single-crystalline beta-K(0.33)V(2)O(5) nanorods. As expected, both the temperature-dependence of the resistivity and magnetization demonstrated MITs at about 72 K for beta-K(0.33)V(2)O(5), thus matching well with the linear relationship described above. The beta-K(0.33)V(2)O(5) was assigned as a new member of the beta-A(0.33)V(2)O(5) bronze family for their similar crystal and electronic structures and their MIT property; this addition enriches the beta-A(0.33)V(2)O(5) bronze family.

  20. Metal-insulator transition in Ba3Fe1 -xRu2 +xO9 : Interplay between site disorder, chemical percolation, and electronic structure

    Science.gov (United States)

    Middey, S.; Aich, Payel; Meneghini, C.; Mukherjee, K.; Sampathkumaran, E. V.; Siruguri, V.; Mahadevan, P.; Ray, Sugata

    2016-11-01

    Perovskites containing barium metal at the A site often take up unusual hexagonal structures having more than one type of possible sites for the B cation to occupy. This opens up various different B -B - or B -O-B -type connectivities and consequent physical properties which are naturally missing in cubic perovskites. BaRuO3 is one such system where doping of Ru (4 d4 ) by other transition metals (Mn +) creates similar conditions, giving rise to various M -Ru interactions. Interestingly, the 6 H hexagonal structure of doped barium ruthenate triple perovskite (Ba3M Ru2O9 ) seems to possess some internal checks because within the structure M ion always occupies the 2 a site and Ru goes to the 4 f site, allowing only M -O-Ru 180∘ and Ru-O-Ru 90∘ interactions to occur. The only exception is observed in the case of the Fe dopant, which allows us to study almost the full Ba3Fe1 -xRu2 +xO9 series of compounds with wide ranges of x because here Fe ions have the ability to freely go to the 4 f sites and Ru readily takes up the 2 a positions. Therefore, here one has the opportunity to probe the evolution of electronic and magnetic properties as a function of doping by going from BaRuO3 (paramagnetic metal) to BaFeO3 (ferromagnetic insulator). Our detailed experimental and theoretical results show that the series does exhibit a percolative metal-insulator transition with an accompanying but not coincidental magnetic transition as a function of x .

  1. Metal-insulator transition in AC{sub 60}:RbC{sub 60} and KC{sub 60}

    Energy Technology Data Exchange (ETDEWEB)

    Khazeni, K.; Crespi, V.H.; Hone, J.; Zettl, A.; Cohen, M.L. [Department of Physics, University of California at Berkeley, Berkeley, California 94720 (United States)]|[Materials Sciences Division, Lawrence Berkeley Laboratory, Berkeley, California 94720 (United States)

    1997-09-01

    At zero pressure polymerized RbC{sub 60} is an insulator, whereas polymerized KC{sub 60} is a metal with a slight low-temperature resistive upturn. We report measurements of the resistivity of RbC{sub 60} under pressure, finding a hysteretic resistive transition in RbC{sub 60} near 200 K at 5 kbar, at which point the material transforms from insulator to metal. Correcting the resistivity to constant volume, both materials are metallic below the transition with a common low-temperature resistive upturn which is suppressed under compression. {copyright} {ital 1997} {ital The American Physical Society}

  2. Ultrafast photo-induced metal insulator transition in 1/4 filled organic crystal (EDO-TTF)2PF6

    Science.gov (United States)

    Chollet, Matthieu; Guerin, Laurent; Uchida, Naoki; Fukaya, Souichi; Shimoda, Hiroaki; Ishikawa, Tadahiko; Matsuda, Kazunari; Hasegawa, Takumi; Ota, Akira; Yamochi, Hideki; Saito, Gunzi; Tazaki, Ryoko; Adachi, Shin-ichi; Koshihara, Shin-ya

    2005-01-01

    We report that the 1/4 filled A2B salt (EDO-TTF)2PF6 developed as a candidate for organic superconductor unexpectedly shows highly sensitive and ultra-fast photo-induced phase transition (PIPT) from insulator (I) to metal (M). We show the results of time resolved experiments performed on this crystal. A large reflectivity change in the near infrared region (1.2-2 eV), which occurs within 2 ps for weak excitation intensity, has been observed. We also observed coherent vibrations in the dynamical process of this transition.

  3. Metal-Insulator Transitions in Epitaxial LaVO(3) and LaTiO(3) Films

    Science.gov (United States)

    2012-08-01

    semiconductors C. He, T. Sanders, M. Gray, F. Wong, V. Mehta, Y. Suzuki University of Iowa @ Iowa City Office of Sponsored Programs The University of Iowa...are insulating in the bulk—has led to an explosion of research activity in perovskite transition-metal oxide heterostructures. The most well-known

  4. Transport properties and metal-insulator transition in oxygen deficient LaNiO3: a density functional theory study

    Science.gov (United States)

    Misra, D.; Kundu, T. K.

    2016-09-01

    Density functional theory with appropriate functional has been employed to investigate the metal to insulator transition in oxygen deficient LaNiO3-x (x = 0.0, 0.25, 0.5, 1.0) compounds. While the metallic nature of LaNiO3 is characterized by the low temperature Fermi liquid behavior of resistivity and a finite density of states at the Fermi level, the density of states and the transport properties clearly identify LaNiO2.75 as a semiconductor, and LaNiO2.5 as an insulator, which is followed by another insulator to semiconductor transition with further increase of x to ‘1’ in LaNiO2. This oxygen vacancy controlled metal to insulator transition is explained on the basis of non-adiabatic polaronic transport. From the covalency metric calculation of the chemical bonding and the Bader charge transfer analysis, this metal to insulator transition is attributed to the enhanced covalent part in the chemical bonding and reduced charge transfer from Ni to O atoms in LaNiO3-x compounds.

  5. Metal-Insulator-Semiconductor Photodetectors

    Directory of Open Access Journals (Sweden)

    Chu-Hsuan Lin

    2010-09-01

    Full Text Available The major radiation of the Sun can be roughly divided into three regions: ultraviolet, visible, and infrared light. Detection in these three regions is important to human beings. The metal-insulator-semiconductor photodetector, with a simpler process than the pn-junction photodetector and a lower dark current than the MSM photodetector, has been developed for light detection in these three regions. Ideal UV photodetectors with high UV-to-visible rejection ratio could be demonstrated with III-V metal-insulator-semiconductor UV photodetectors. The visible-light detection and near-infrared optical communications have been implemented with Si and Ge metal-insulator-semiconductor photodetectors. For mid- and long-wavelength infrared detection, metal-insulator-semiconductor SiGe/Si quantum dot infrared photodetectors have been developed, and the detection spectrum covers atmospheric transmission windows.

  6. Metal-insulator-semiconductor photodetectors.

    Science.gov (United States)

    Lin, Chu-Hsuan; Liu, Chee Wee

    2010-01-01

    The major radiation of the sun can be roughly divided into three regions: ultraviolet, visible, and infrared light. Detection in these three regions is important to human beings. The metal-insulator-semiconductor photodetector, with a simpler process than the pn-junction photodetector and a lower dark current than the MSM photodetector, has been developed for light detection in these three regions. Ideal UV photodetectors with high UV-to-visible rejection ratio could be demonstrated with III-V metal-insulator-semiconductor UV photodetectors. The visible-light detection and near-infrared optical communications have been implemented with Si and Ge metal-insulator-semiconductor photodetectors. For mid- and long-wavelength infrared detection, metal-insulator-semiconductor SiGe/Si quantum dot infrared photodetectors have been developed, and the detection spectrum covers atmospheric transmission windows.

  7. Size-dependent metal-insulator transition in platinum-dispersed silicon dioxide thin film: A candidate for future non-volatile memory

    Science.gov (United States)

    Chen, Albert B. K.

    Non-volatile random access memories (NVRAM) are promising data storage and processing devices. Various NVRAM, such as FeRAM and MRAM, have been studied in the past. But resistance switching random access memory (RRAM) has demonstrated the most potential for replacing flash memory in use today. In this dissertation, a novel RRAM material design that relies upon an electronic transition, rather than a phase change (as in chalcogenide Ovonic RRAM) or a structural change (such in oxide and halide filamentary RRAM), is investigated. Since the design is not limited to a single material but applicable to general combinations of metals and insulators, the goal of this study is to use a model material to delineate the intrinsic features of the electronic metal/insulator transition in random systems and to demonstrate their relevance to reliable memory storage and retrieval. We fabricated amorphous SiO2 thin films embedded with randomly dispersed Pt atoms. Macroscopically, this random material exhibits a percolation transition in electric conductivity similar to the one found in various insulator/metal granular materials. However, at Pt concentrations well below the bulk percolation limit, a distinct insulator to metal transition occurs in the thickness direction as the film thickness falls below electron's "diffusion" distance, which is the tunneling distance at 0K. The thickness-triggered metal- to-insulator transition (MIT) can be similarly triggered by other conditions: (a) a changing Pt concentration (a concentration-triggered MIT), (b) a changing voltage/polarity (voltage-triggered MIT), and (c) an UV irradiation (photon-triggered MIT). The resistance switching characteristics of this random material were further investigated in several device configurations under various test conditions. These include: materials for the top and bottom electrodes, fast pulsing, impedance spectroscopy, static stressing, retention, fatigue and temperature from 10K to 448K. The SiO2-Pt

  8. Metal-insulator transition in Nd{sub 1−x}Eu{sub x}NiO{sub 3}: Entropy change and electronic delocalization

    Energy Technology Data Exchange (ETDEWEB)

    Jardim, R. F., E-mail: rjardim@if.usp.br; Andrade, S. [Instituto de Física, Universidade de São Paulo, CP 66318, São Paulo 05315-970 (Brazil); Barbeta, V. B. [Departamento de Física, Centro Universitário da FEI, São Bernardo do Campo 09850-901 (Brazil); Escote, M. T. [Centro de Engenharia, Modelagem e Ciências Sociais Aplicadas, Universidade Federal do ABC, Santo André 09210-170 (Brazil); Cordero, F. [CNR-ISC, Istituto dei Sistemi Complessi, Area della Ricerca di Roma - Tor Vergata, Via del Fosso del Cavaliere 100, I-00133 Rome (Italy); Torikachvili, M. S. [Department of Physics, San Diego State University, San Diego, California 92182-1233 (United States)

    2015-05-07

    The metal-insulator (MI) phase transition in Nd{sub 1–x}Eu{sub x}NiO{sub 3}, 0 ≤ x ≤ 0.35, has been investigated through the pressure dependence of the electrical resistivity ρ(P, T) and measurements of specific heat C{sub P}(T). The MI transition temperature (T{sub MI}) increases with increasing Eu substitution and decreases with increasing pressure. Two distinct regions for the Eu dependence of dT{sub MI}/dP were found: (i) for x ≤ 0.15, dT{sub MI}/dP is nearly constant and ∼−4.3 K/kbar; (ii) for x ≥ 0.15, dT{sub MI}/dP increases with x and it seems to reach a saturation value ∼−6.2 K/kbar for the x = 0.35 sample. This change is accompanied with a strong decrease in the thermal hysteresis in ρ(P, T) between the cooling and warming cycles, observed in the vicinity of T{sub MI}. The entropy change (ΔS) at T{sub MI} for the sample x = 0, estimated by using the dT{sub MI}/dP data and the Clausius-Clapeyron equation, resulted in ΔS ∼ 1.2 J/mol K, a value in line with specific heat measurements. When the Eu concentration is increased, the antiferromagnetic (AF) and the MI transitions are separated in temperature, permitting that an estimate of the entropy change due to the AF/Paramagnetic transition be carried out, yielding ΔS{sub M} ∼ 200 mJ/mol K. This value is much smaller than that expected for a s = 1/2 spin system. The analysis of ρ(P, T) and C{sub P}(T) data indicates that the entropy change at T{sub MI} is mainly due to the electronic delocalization and not related to the AF transition.

  9. Superconductivity and crystal structural origins of the metal-insulator transition in Ba6 -xSrxNb10O30 tetragonal tungsten bronzes

    Science.gov (United States)

    Kolodiaznyi, Taras; Sakurai, Hiroya; Isobe, Masaaki; Matsushita, Yoshitaka; Forbes, Scott; Mozharivskyj, Yurij; Munsie, Timothy J. S.; Luke, Graeme M.; Gurak, Mary; Clarke, David R.

    2015-12-01

    Ba6 -xSrxNb10O30 solid solution with 0 ≤ x ≤6 forms the filled tetragonal tungsten bronze (TTB) structure. The Ba-end member crystallizes in the highest symmetry P 4 /m b m space group (a =b =12.5842 (18 )Å and c =3.9995 (8 )Å ) and so do all the compositions with 0 ≤ x ≤5 . The Sr-end member of the solid solution crystallizes in the tentatively assigned A m a m space group (a *=17.506 (4 )Å , b *=34.932 (7 )Å , and c *=7.7777 (2 )Å ). The latter space group is related to the parent P 4 /m b m TTB structure as a * ≈ √{2 }a ,b * ≈2 √{2 }a ,c *=2 c . Low-temperature specific heat measurements indicate that the Ba-rich compositions with x ≤2 are conventional BCS superconductors with TC ≤1.6 K and superconducting energy gaps of ≤0.38 meV. The values of the TC in the cation-filled Nb-based TTBs reported here are comparable with those of the unfilled KxWO3 and NaxWO3 TTBs having large alkali ion deficiency. As the unit cell volume decreases with increasing x , an unexpected metal-insulator transition (MIT) in Ba6 -xSrxNb10O30 occurs at x ≥3 . We discuss the possible origins of the MIT in terms of the carrier concentration, symmetry break, and Anderson localization.

  10. Correlation-induced metal-insulator transitions in d{sup 0} magnetic superlattices based on alkaline-earth monoxides: Insights from ab initio calculations

    Energy Technology Data Exchange (ETDEWEB)

    Lu, Yi-Lin [Department of Applied Physics, Institute of Advanced Materials Physics, Tianjin Key Laboratory of Low Dimensional Materials Physics and Preparing Technology, Faculty of Science, Tianjin University, Tianjin 300072 (China); Dong, Shengjie [Department of Physics, Tianjin Normal University, Tianjin 300387 (China); Zhou, Baozeng [Department of Applied Physics, Institute of Advanced Materials Physics, Tianjin Key Laboratory of Low Dimensional Materials Physics and Preparing Technology, Faculty of Science, Tianjin University, Tianjin 300072 (China); Zhao, Hui [Department of Physics, Tianjin Normal University, Tianjin 300387 (China); Wu, Ping, E-mail: pingwu@tju.edu.cn [Department of Applied Physics, Institute of Advanced Materials Physics, Tianjin Key Laboratory of Low Dimensional Materials Physics and Preparing Technology, Faculty of Science, Tianjin University, Tianjin 300072 (China)

    2015-06-15

    Using first-principles density functional theory calculations, we have investigated the electronic structure and magnetic properties of four superlattices (MO){sub 1}/(MX){sub 1} (001) (M=Ca and Sr; X=N and C). Our results show that compared with standard GGA approach, the GGA plus effective U{sub eff} scheme can correct electronic structure and magnetic properties in some extent. With enhancing electronic correlation, for (CaO){sub 1}/(CaN){sub 1}, (SrO){sub 1}/(SrN){sub 1}, and (SrO){sub 1}/(SrC){sub 1}, the bands across Fermi level are divided into two parts and the shape of isotropic spherical spin atmosphere becomes anisotropic dumbbell-like with specific orientation, accompanying metal-insulator transitions. For (CaO){sub 1}/(CaC){sub 1}, the states just smearing with the Fermi level shift to lower energy region below Fermi level, indicating the transformation from a nearly half metal to an actual half metal occurs. The different behavior of (CaO){sub 1}/(CaC){sub 1} compared with three other compounds may be caused by the larger ionization energy of calcium than that of strontium and the smaller electronegativity of carbon than that of nitrogen. - Highlights: • The magnetic behaviors of four d{sup 0} superlattices are investigated. • The enhanced electronic correlation influences the magnetic properties. • (CaO){sub 1}/(CaC){sub 1} transforms from a nearly half metal to an actual half metal. • The other three compounds transform from half metals to magnetic insulators.

  11. Theory of the magnetic and metal-insulator transitions in RNiO3 bulk and layered structures.

    Science.gov (United States)

    Lau, Bayo; Millis, Andrew J

    2013-03-22

    A slave rotor--Hartree-Fock formalism is presented for studying the properties of the p-d model describing perovskite transition metal oxides, and a flexible and efficient numerical formalism is developed for its solution. The methodology is shown to yield, within a unified formulation, the significant aspects of the rare-earth nickelate phase diagram, including the paramagnetic metal state observed for the LaNiO3 and the correct ground-state magnetic order of insulating compounds. It is then used to elucidate ground state changes occurring as morphology is varied from bulk to strained and unstrained thin-film form. For ultrathin films, epitaxial strain and charge transfer to the apical out-of-plane oxygen sites are shown to have significant impact on the phase diagram.

  12. Theory of the magnetic and metal-insulator transitions in RNiO3 bulk and layered

    Science.gov (United States)

    Lau, Bayo; Millis, Andrew J.

    2013-03-01

    A slave rotor-Hartree Fock formalism is presented for studying the properties of the p-d model describing perovskite transition metal oxides, and a flexible and efficient numerical formalism is developed for its solution. The methodology is shown to yield, within an unified formulation, the significant aspects of the rare earth nickelate phase diagram, including the paramagnetic metal state observed for the LaNiO3 and the correct ground-state magnetic order of insulating compounds. It is then used to elucidate ground state changes occurring as morphology is varied from bulk to strained and un-strained thin-film form. For ultrathin films, epitaxial strain and charge-transfer to the apical out-of-plane oxygen sites are shown to have significant impact on the phase diagram. This effort is supported by US National Science Foundation under grant NSF-DMR-1006282

  13. Theory of the Magnetic and Metal-Insulator Transitions in RNiO3 Bulk and Layered Structures

    Science.gov (United States)

    Lau, Bayo; Millis, Andrew J.

    2013-03-01

    A slave rotor—Hartree-Fock formalism is presented for studying the properties of the p-d model describing perovskite transition metal oxides, and a flexible and efficient numerical formalism is developed for its solution. The methodology is shown to yield, within a unified formulation, the significant aspects of the rare-earth nickelate phase diagram, including the paramagnetic metal state observed for the LaNiO3 and the correct ground-state magnetic order of insulating compounds. It is then used to elucidate ground state changes occurring as morphology is varied from bulk to strained and unstrained thin-film form. For ultrathin films, epitaxial strain and charge transfer to the apical out-of-plane oxygen sites are shown to have significant impact on the phase diagram.

  14. The metal-insulator transition in vanadium dioxide: A view at bulk and surface contributions for thin films and the effect of annealing

    Science.gov (United States)

    Yin, W.; West, K. G.; Lu, J. W.; Pei, Y.; Wolf, S. A.; Reinke, P.; Sun, Y.

    2009-06-01

    Vanadium dioxide is investigated as potential oxide barrier in spin switches, and in order to incorporate VO2 layers in complex multilayer devices, it is necessary to understand the relation between bulk and surface/interface properties. Highly oriented VO2 thin films were grown on (0001) sapphire single crystal substrates with reactive bias target ion beam deposition. In the analysis of the VO2 films, bulk-sensitive methods [x-ray diffraction (XRD) and transport measurements] and surface sensitive techniques [photoelectron spectroscopy (PES) and scanning tunneling microscopy and spectroscopy] were employed. The samples were subjected to heating cycles with annealing temperatures of up to 425 and 525K. Prior to annealing the VO2 films exhibit the transition from the monoclinic to the tetragonal phase with the concurrent change in conductivity by more than a factor of 103 and their phase purity is confirmed by XRD. Annealing to 425K and thus cycling across the metal-insulator transition (MIT) temperature has no impact on the bulk properties of the VO2 film but the surface undergoes irreversible electronic changes. The observation of the valence band with PES during the annealing illustrates that the surface adopts a partially metallic character, which is retained after cooling. Annealing to a higher temperature (525K ) triggers a modification of the bulk, which is evidenced by a considerable reduction in the MIT characteristics, and a degradation in crystallite morphology. The local measurement of the conductivity with scanning tunneling spectroscopy shows the transition of the surface from predominantly semiconducting surface prior to annealing to a surface with an overwhelming contribution from metallic sections afterward. The spatial distribution of metallic regions cannot be linked in a unique manner to the crystallite size or location within the crystallites. The onset of oxygen depletion at the surface is held responsible for this behavior. The onset of bulk

  15. Studies on magnetic-field-induced first-order transitions

    Indian Academy of Sciences (India)

    P Chaddah

    2006-07-01

    We shall discuss magnetization and transport measurements in materials exhibiting a broad first-order transition. The phase transitions would be caused by varying magnetic field as well as temperature, and we concentrate on ferro- to antiferromagnetic transitions in magnetic materials. We distinguish between metastable supercooled phases and metastable glassy phase.

  16. MAGNETIC FIELD INDUCED FIRST-ORDER TRANSITIONS IN DYSPROSIUM ORTHOFERRITE

    OpenAIRE

    Eremenko, V.; Gnatchenko, S.; Kharchenko, N.; Lebedev, P.; Piotrowski, K; Szymczak, H.; Szymczak, R.

    1988-01-01

    New type of magnetic first-order phase transition induced by external magnetic field applied in the ab-plane in DyFeO3 is investigated using different magnetooptic techniques. The phenomenological model of this transition is proposed. The phase diagram in H-T plane has been obtained for various H orientation in the ab-plane.

  17. Metal-insulator transition and tunable Dirac-cone surface state in the topological insulator TlBi1 -xSbxTe2 studied by angle-resolved photoemission

    Science.gov (United States)

    Trang, Chi Xuan; Wang, Zhiwei; Yamada, Keiko; Souma, Seigo; Sato, Takafumi; Takahashi, Takashi; Segawa, Kouji; Ando, Yoichi

    2016-04-01

    We report a systematic angle-resolved photoemission spectroscopy on topological insulator (TI) TlBi1 -xSbxTe2 which is bulk insulating at 0.5 ≲x ≲0.9 and undergoes a metal-insulator-metal transition with the Sb content x . We found that this transition is characterized by a systematic hole doping with increasing x , which results in the Fermi-level crossings of the bulk conduction and valence bands at x ˜0 and x ˜1 , respectively. The Dirac point of the topological surface state is gradually isolated from the valence-band edge, accompanied by a sign reversal of Dirac carriers. We also found that the Dirac velocity is the largest among known solid-solution TI systems. The TlBi1 -xSbxTe2 system thus provides an excellent platform for Dirac-cone engineering and device applications of TIs.

  18. Near-Field Nanoscopy of Metal-Insulator Phase Transitions Towards Synthesis of Novel Correlated Transition Metal Oxides and Their Interaction with Plasmon Resonances

    Science.gov (United States)

    2016-01-05

    Nanolayer and two-dimensional (2D) materials 9 such as grapheme 10, 11, boron nitride 9, 12, transition metal dichalcogenides 9, 13-16 (TMDCs), and... plasma frequency ≈ 0.4pω eV, carrier density . 11 11 1 10 cm−≈ ×n and the thickness of the surface metallic layer of ~ 1 nm . We have also...observed similar behavior in other nanolayer semiconductors such as TMDC MoS2 and topological insulator Bi2Te3 but not in insulators such as boron nitride

  19. Nature of unusual spontaneous and field-induced phase transitions in multiferroics RMn 2O 5

    Science.gov (United States)

    Pyatakov, A. P.; Kadomtseva, A. M.; Vorob'ev, G. P.; Popov, Yu. F.; Krotov, S. S.; Zvezdin, A. K.; Lukina, M. M.

    2009-04-01

    Complex magnetic, magnetoelectric and magnetoelastic studies of spontaneous and field-induced phase transitions in TmMn 2O 5 were carried out. In the vicinity of spontaneous phase transition temperatures (35 and 25 K) the magnetoelectric and magnetoelastic dependences demonstrated the jumps of polarization and magnetostriction induced by the field ˜150 kOe. These anomalies can be attributed to the influence of magnetic field on the conditions of incommensurate-commensurate phase transition at 35 K and the reverse one at 25 K. In b-axis dependences the magnetic field-induced spin-reorientation phase transition was also observed below 20 K. Finally the magnetoelectric anomaly associated with metamagnetic transition is observed below the temperature of rare-earth subsystem ordering at relatively small critical fields of 5 kOe. This variety of spontaneous and induced phase transitions in RMn 2O 5 stems from the interplay of three magnetic subsystems: Mn 3+, Mn 4+, R 3+. The comparison with YMn 2O 5 highlights the role of rare earth in low-temperature region (metamagnetic and spin-reorientation phase transitions), while the phase transition at higher temperatures between incommensurate and commensurate phases should be ascribed to the different temperature dependences of Mn 3+ and Mn 4+ ions. The strong correlation of magnetoelastic and magnetoelectric properties observed in the whole class of RMn 2O 5 highlights their multiferroic nature.

  20. Temperature and magnetic field induced multiple magnetic transitions in DyAg(2).

    Science.gov (United States)

    Arora, Parul; Chattopadhyay, M K; Sharath Chandra, L S; Sharma, V K; Roy, S B

    2011-02-09

    The magnetic properties of the rare-earth intermetallic compound DyAg(2) are studied in detail with the help of magnetization and heat capacity measurements. It is shown that the multiple magnetic phase transitions can be induced in DyAg(2) both by temperature and magnetic field. The detailed magnetic phase diagram of DyAg(2) is determined experimentally. It was already known that DyAg(2) undergoes an incommensurate to commensurate antiferromagnetic phase transition close to 10 K. The present experimental results highlight the first order nature of this phase transition, and show that this transition can be induced by magnetic field as well. It is further shown that another isothermal magnetic field induced transition or metamagnetic transition exhibited by DyAg(2) at still lower temperatures is also of first order nature. The multiple magnetic phase transitions in DyAg(2) give rise to large peaks in the temperature dependence of the heat capacity below 17 K, which indicates its potential as a magnetic regenerator material for cryocooler related applications. In addition it is found that because of the presence of the temperature and field induced magnetic phase transitions, and because of short range magnetic correlations deep inside the paramagnetic regime, DyAg(2) exhibits a fairly large magnetocaloric effect over a wide temperature window, e.g., between 10 and 60 K.

  1. Control of magnetic relaxation by electric-field-induced ferroelectric phase transition and inhomogeneous domain switching

    Energy Technology Data Exchange (ETDEWEB)

    Nan, Tianxiang; Emori, Satoru; Wang, Xinjun; Hu, Zhongqiang; Xie, Li; Gao, Yuan; Lin, Hwaider; Sun, Nian, E-mail: n.sun@neu.edu [Department of Electrical and Computer Engineering, Northeastern University, Boston, Massachusetts 02115 (United States); Peng, Bin; Liu, Ming, E-mail: mingliu@mail.xjtu.edu.cn [Electronic Materials Research Laboratory, Xi' an Jiaotong University, Xi' an 710049 (China); Jiao, Jie; Luo, Haosu [Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 201800 (China); Budil, David [Department of Chemistry, Northeastern University, Boston, Massachusetts 02115 (United States); Jones, John G.; Howe, Brandon M.; Brown, Gail J. [Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright-Patterson AFB, Ohio 45433 (United States)

    2016-01-04

    Electric-field modulation of magnetism in strain-mediated multiferroic heterostructures is considered a promising scheme for enabling memory and magnetic microwave devices with ultralow power consumption. However, it is not well understood how electric-field-induced strain influences magnetic relaxation, an important physical process for device applications. Here, we investigate resonant magnetization dynamics in ferromagnet/ferroelectric multiferroic heterostructures, FeGaB/PMN-PT and NiFe/PMN-PT, in two distinct strain states provided by electric-field-induced ferroelectric phase transition. The strain not only modifies magnetic anisotropy but also magnetic relaxation. In FeGaB/PMN-PT, we observe a nearly two-fold change in intrinsic Gilbert damping by electric field, which is attributed to strain-induced tuning of spin-orbit coupling. By contrast, a small but measurable change in extrinsic linewidth broadening is attributed to inhomogeneous ferroelastic domain switching during the phase transition of the PMN-PT substrate.

  2. Control of magnetic relaxation by electric-field-induced ferroelectric phase transition and inhomogeneous domain switching

    Science.gov (United States)

    Nan, Tianxiang; Emori, Satoru; Peng, Bin; Wang, Xinjun; Hu, Zhongqiang; Xie, Li; Gao, Yuan; Lin, Hwaider; Jiao, Jie; Luo, Haosu; Budil, David; Jones, John G.; Howe, Brandon M.; Brown, Gail J.; Liu, Ming; Sun, Nian

    2016-01-01

    Electric-field modulation of magnetism in strain-mediated multiferroic heterostructures is considered a promising scheme for enabling memory and magnetic microwave devices with ultralow power consumption. However, it is not well understood how electric-field-induced strain influences magnetic relaxation, an important physical process for device applications. Here, we investigate resonant magnetization dynamics in ferromagnet/ferroelectric multiferroic heterostructures, FeGaB/PMN-PT and NiFe/PMN-PT, in two distinct strain states provided by electric-field-induced ferroelectric phase transition. The strain not only modifies magnetic anisotropy but also magnetic relaxation. In FeGaB/PMN-PT, we observe a nearly two-fold change in intrinsic Gilbert damping by electric field, which is attributed to strain-induced tuning of spin-orbit coupling. By contrast, a small but measurable change in extrinsic linewidth broadening is attributed to inhomogeneous ferroelastic domain switching during the phase transition of the PMN-PT substrate.

  3. Magnetostrictive hypersound generation by spiral magnets in the vicinity of magnetic field induced phase transition

    Science.gov (United States)

    Bychkov, Igor V.; Kuzmin, Dmitry A.; Kamantsev, Alexander P.; Koledov, Victor V.; Shavrov, Vladimir G.

    2016-11-01

    In present work we have investigated magnetostrictive ultrasound generation by spiral magnets in the vicinity of magnetic field induced phase transition from spiral to collinear state. We found that such magnets may generate transverse sound waves with the wavelength equal to the spiral period. We have examined two types of spiral magnetic structures: with inhomogeneous exchange and Dzyaloshinskii-Moriya interactions. Frequency of the waves from exchange-caused spiral magnetic structure may reach some THz, while in case of Dzyaloshinskii-Moriya interaction-caused spiral it may reach some GHz. These waves will be emitted like a sound pulses. Amplitude of the waves is strictly depends on the phase transition speed. Some aspects of microwaves to hypersound transformation by spiral magnets in the vicinity of phase transition have been investigated as well. Results of the work may be interesting for investigation of phase transition kinetics as well, as for various hypersound applications.

  4. Study of high temperature metal-insulator phase transition in La{sub 1−x}Ca{sub x}MnO{sub 3} employing in-situ ultrasonic studies

    Energy Technology Data Exchange (ETDEWEB)

    Arunachalam, M.; Thamilmaran, P. [Department of Physics, Sri SRNM College, Sattur 626 203, Tamil Nadu (India); Manonmanium Sundaranar University, Tirunelveli 627 012, Tamil Nadu (India); Sankarrajan, S. [Department of Physics, Unnamalai Institute of Technology, Kovilpatti 628 503, Tamil Nadu (India); Sakthipandi, K., E-mail: sakthipandi@gmail.com [Department of Physics, Sethu Institute of Technology, Kariapatti 626 115, Tamil Nadu (India)

    2015-01-01

    Bulk La{sub 1−x}Ca{sub x}MnO{sub 3} (x=0.70, 0.75 and 0.90) perovskite samples were synthesized using solid state reaction technique. X-ray diffraction study on the sample indicates that the sample has single phase orthorhombic structure with a space group of pnma and has no secondary phase. By employing through transmission technique operated at a fundamental frequency of 5 MHz, ultrasonic velocities and attenuation were measured for both longitudinal and shear waves over a wide range of temperature from 300 to 700 K. The ultrasonic parameters showed an anomalous behavior at the transition temperature 640, 560 and 370 K for x=0.70, 0.75 and 0.90, respectively. These anomalies in the ultrasonic parameters were used to explain the second order metal-insulator phase transition. The existence of the single-ion magnetostriction in LCMO perovskite manganites is also revealed from the ultrasonic measurements.

  5. Magnetization Studies of Field-Induced Transitions by Using a Single-Turn Coil Technique

    Science.gov (United States)

    Abe, N.; Matsuda, Y. H.; Takeyama, S.; Sato, K.; Kageyama, H.; Nishiwaki, Y.

    2013-03-01

    Some technical improvements for magnetization measurements using a vertical-type single-turn coil (V-STC) method have been attempted. We have chosen LaCoO3, RbCoBr3 and SrCu2(BO3)2 that show interesting field induced magnetic transitions, as test materials. Intriguing features were clearly observed in magnetic fields of up to 100 T. The quality of the data is of comparable to those obtained by a conventional non-destructive pulse magnet.

  6. Manganese-induced magnetic symmetry breaking and its correlation with the metal-insulator transition in bilayered S r3(Ru1-xM nx) 2O7

    Science.gov (United States)

    Zhang, Qiang; Ye, Feng; Tian, Wei; Cao, Huibo; Chi, Songxue; Hu, Biao; Diao, Zhenyu; Tennant, David A.; Jin, Rongying; Zhang, Jiandi; Plummer, Ward

    2017-06-01

    Bilayered S r3R u2O7 is an unusual metamagnetic metal with inherently antiferromagnetic (AFM) and ferromagnetic (FM) fluctuations. Partial substitution of Ru by Mn results in the establishment of a metal-insulator transition (MIT) at TMIT and AFM ordering at TM in S r3(Ru1-xM nx) 2O7 . Using elastic neutron scattering, we investigated the effect of Mn doping on the magnetic structure, in-plane magnetic correlation lengths and their correlation to the MIT in S r3(Ru1-xM nx) 2O7 (x =0.06 and 0.12). With the increase of Mn doping (x ) from 0.06 to 0.12 or the decrease of temperatures for x =0.12 , an evolution from an in-plane short-range to long-range antiferromagnetic (AFM) ground state occurs. For both compounds, the magnetic ordering has a double-stripe configuration, and the onset of magnetic correlation with an anisotropic behavior coincides with the sharp rise in electrical resistivity and specific heat. Since it does not induce a measurable lattice distortion, the double-stripe antiferromagnetic order with anisotropic spin texture breaks symmetry from a C4 v crystal lattice to a C2 v magnetic sublattice. These observations shed light on an age-old question regarding the Slater versus Mott-type MIT.

  7. Magnetostrictive hypersound generation by spiral magnets in the vicinity of magnetic field induced phase transition

    Energy Technology Data Exchange (ETDEWEB)

    Bychkov, Igor V. [Chelyabinsk State University, 129 Br. Kashirinykh Str., Chelyabinsk 454001 (Russian Federation); South Ural State University (National Research University), 76 Lenin Prospekt, Chelyabinsk 454080 (Russian Federation); Kuzmin, Dmitry A., E-mail: kuzminda@csu.ru [Chelyabinsk State University, 129 Br. Kashirinykh Str., Chelyabinsk 454001 (Russian Federation); South Ural State University (National Research University), 76 Lenin Prospekt, Chelyabinsk 454080 (Russian Federation); Kamantsev, Alexander P.; Koledov, Victor V.; Shavrov, Vladimir G. [Kotelnikov Institute of Radio-engineering and Electronics of RAS, Mokhovaya Street 11-7, Moscow 125009 (Russian Federation)

    2016-11-01

    In present work we have investigated magnetostrictive ultrasound generation by spiral magnets in the vicinity of magnetic field induced phase transition from spiral to collinear state. We found that such magnets may generate transverse sound waves with the wavelength equal to the spiral period. We have examined two types of spiral magnetic structures: with inhomogeneous exchange and Dzyaloshinskii–Moriya interactions. Frequency of the waves from exchange-caused spiral magnetic structure may reach some THz, while in case of Dzyaloshinskii–Moriya interaction-caused spiral it may reach some GHz. These waves will be emitted like a sound pulses. Amplitude of the waves is strictly depends on the phase transition speed. Some aspects of microwaves to hypersound transformation by spiral magnets in the vicinity of phase transition have been investigated as well. Results of the work may be interesting for investigation of phase transition kinetics as well, as for various hypersound applications. - Highlights: • Magnetostrictive ultrasound generation by spiral magnets at phase transition (PT) is studied. • Spiral magnets during PT may generate transverse sound with wavelength equal to spiral period. • Amplitude of the sound is strictly depends on the phase transition speed. • Microwave-to-sound transformation in the vicinity of PT is investigated as well.

  8. Magnetic field induced 1st order transitions: Recent studies, and some new concepts

    Science.gov (United States)

    Chaddah, P.

    2015-05-01

    Phase transitions are caused by varying temperature, or pressure, or magnetic field. The observation of 1st order magneto-structural transitions has created application possibilities based on magnetoresistance, magnetocaloric effect, magnetic shape memory effect, and magneto-dielectric effect. Magnetic field induced transitions, and phase coexistence of competing magnetic phases down to the lowest temperature, gained prominence over a decade ago with theoretical models suggesting that the ground state is not homogeneous. Researchers at Indore pushed an alternative view that this phase coexistence could be due to glasslike "kinetic arrest" of a disorder-broadened first-order magnetic transition between two states with long-range magnetic order, resulting in phase coexistence down to the lowest temperatures. The CHUF (cooling and heating in unequal field) protocol created at Indore allows the observation of `devitrification', followed by `melting'. I show examples of measurements establishing kinetic arrest in various materials, emphasizing that glasslike arrest of 1st order magnetic transitions may be as ubiquitous as glass formation following the arrest of 1st order structural transitions.

  9. Field induced magnetic phase transition as a magnon Bose Einstein condensation

    Directory of Open Access Journals (Sweden)

    Teodora Radu et al

    2007-01-01

    Full Text Available We report specific heat, magnetocaloric effect and magnetization measurements on single crystals of the frustrated quasi-2D spin -½ antiferromagnet Cs2CuCl4 in the external magnetic field 0≤B≤12 T along a-axis and in the temperature range 0.03 K≤T≤6 K. Decreasing the applied magnetic field B from high fields leads to the closure of the field induced gap in the magnon spectrum at a critical field Bcsimeq8.44 T and a long-range incommensurate state below Bc. In the vicinity of Bc, the phase transition boundary is well described by the power law TN~(Bc-B1/phi with the measured critical exponent phisimeq1.5. These findings provide experimental evidence that the scaling law of the transition temperature TN can be described by the universality class of 3D Bose–Einstein condensation (BEC of magnons.

  10. Vacuum Particle-Antiparticle Creation in Strong Fields as a Field-Induced Phase Transition

    Science.gov (United States)

    Smolyansky, S. A.; Panferov, A. D.; Blaschke, D. B.; Juchnowski, L.; Kämpfer, B.; Otto, A.

    2017-03-01

    We study the special features of vacuum particle creation in an external classical field for two simple external field models in standard QED. Our investigation is based on a kinetic equation that is a nonperturbative consequence of the fundamental QED equations of motion. We identify the special features of system evolution that apply qualitatively also for other systems and are therefore rather general. The common basis for a description of these systems is formed by kinetic equations for vacuum particle creation belonging to the class of integro-differential equations of non-Markovian type with fastly oscillating kernel. This allows us to characterize the processes of this type as belonging to the class of field-induced phase transitions. Examples range from condensed matter physics to cosmology.

  11. Vacuum particle-antiparticle creation in strong fields as a field induced phase transition

    CERN Document Server

    Smolyansky, S A; Blaschke, D B; Juchnowski, L; Kaempfer, B; Otto, A

    2016-01-01

    The features of vacuum particle creation in an external classical field are studied for simplest external field models in $3 + 1$ dimensional QED. The investigation is based on a kinetic equation that is a nonperturbative consequence of the fundamental equations of motion of QED. The observed features of the evolution of the system apply on the qualitative level also for systems of other nature and therefore are rather general. Examples from cosmology and condensed matter physics illustrate this statement. The common basis for the description of these systems are kinetic equations for vacuum particle creation belonging to the class of integro-differential equations of non-Markovian type with fastly oscillating kernel. This allows to characterize processes of this type as belonging to the class of field induced phase transitions.

  12. Addendum to "Switching effect and the metal-insulator transition in electric field" by A.L. Pergament et al. [J. Phys. Chem. Solids 71 (2010) 874

    Science.gov (United States)

    Pergament, A. L.; Velichko, A. A.; Stefanovich, G. B.

    2015-02-01

    In the paper mentioned above we reported on the switching mechanism in vanadium dioxide which was shown to be based on the electronically-induced Mott insulator-to-metal transition occurring in conditions of the non-equilibrium carrier density excess in the applied electric field, and the proposed model involved the dependence of the carrier density n on electric field (the Poole-Frenkel effect), as well as the dependence of the critical electric field on n. The data on the n(T) dependence were obtained on the assumption of a temperature-independent carrier mobility μ, and the problem of n reduction at lower temperatures was not fully understood. In this Letter we revisit this problem in the light of some recent data on the μ(T) dependence for VO2. It is shown that the adjusted values of n, taking into account this μ(T), correspond to the Mott critical density within an order of magnitude.

  13. Field-induced crossover from phonon to field assisted hopping conductivity in organic materials

    Science.gov (United States)

    Bourbie, D.

    2011-01-01

    Recently the change in temperature dependence of conductivity observed in polythiophene field-effect transistors has been attributed to field-induced metal-insulator transition. Under a high source-drain voltage, the conductivity becomes independent from temperature and depends exponentially on the inverse of the square root of electric field. In this paper we present a theoretical interpretation of this behavior in the framework of hopping mechanism. The ingredient of this model, is the energy gained from the electrical field is always larger than the energy difference between the localized states involved into the charge transitions, which induces a crossover from phonon-assisted hopping to field-assisted hopping.

  14. Electrical and magnetic properties of n-Cd sub 1 sub - sub x Mn sub x Te close to the metal-insulator transition

    CERN Document Server

    Read, D E

    2001-01-01

    temperatures and in zero field an activated form of the conductivity is observed. In applied magnetic fields (B > 50 mT) Efros-ShkIovskii variable range hopping is observed in the insulating phase. These results are attributed to the formation of a hard gap in the density of states, having a magnetic origin. At higher fields an insulator-metal phase transition occurs. In the metallic phase the conductivity can be described by a quantum correction to the zero temperature conductivity due to the effect of electron-electron interactions. Results obtained before and after illumination are consistent with scaling theory of electron localisation, having a critical exponent close to unity, indicative of the importance of electron-electron interactions. A reduction in the value of the critical field is seen after increasing the carrier density (B sub c = 2.0 and 1.3 T for n = 3.3 and 3.8 x 10 sup 1 sup 7 cm sup - sup 3 respectively). At low temperatures an anisotropy in the resistivity has been measured for samples i...

  15. Electric field-induced superconducting transition of insulating FeSe thin film at 35 K.

    Science.gov (United States)

    Hanzawa, Kota; Sato, Hikaru; Hiramatsu, Hidenori; Kamiya, Toshio; Hosono, Hideo

    2016-04-12

    It is thought that strong electron correlation in an insulating parent phase would enhance a critical temperature (Tc) of superconductivity in a doped phase via enhancement of the binding energy of a Cooper pair as known in high-Tc cuprates. To induce a superconductor transition in an insulating phase, injection of a high density of carriers is needed (e.g., by impurity doping). An electric double-layer transistor (EDLT) with an ionic liquid gate insulator enables such a field-induced transition to be investigated and is expected to result in a high Tc because it is free from deterioration in structure and carrier transport that are in general caused by conventional carrier doping (e.g., chemical substitution). Here, for insulating epitaxial thin films (∼10 nm thick) of FeSe, we report a high Tc of 35 K, which is 4× higher than that of bulk FeSe, using an EDLT under application of a gate bias of +5.5 V. Hall effect measurements under the gate bias suggest that highly accumulated electron carrier in the channel, whose area density is estimated to be 1.4 × 10(15) cm(-2) (the average volume density of 1.7 × 10(21) cm(-3)), is the origin of the high-Tc superconductivity. This result demonstrates that EDLTs are useful tools to explore the ultimate Tc for insulating parent materials.

  16. Giant low field magnetocaloric effect and field-induced metamagnetic transition in TmZn

    Science.gov (United States)

    Li, Lingwei; Yuan, Ye; Zhang, Yikun; Namiki, Takahiro; Nishimura, Katsuhiko; Pöttgen, Rainer; Zhou, Shengqiang

    2015-09-01

    The magnetic properties and the magnetocaloric effect (MCE) in TmZn have been studied by magnetization and heat capacity measurements. The TmZn compound exhibits a ferromagnetic state below a Curie temperature of TC = 8.4 K and processes a field-induced metamagnetic phase transition around and above TC. A giant reversible MCE was observed in TmZn. For a field change of 0-5 T, the maximum values of magnetic entropy change (-ΔSMmax) and adiabatic temperature change (ΔTadmax) are 26.9 J/kg K and 8.6 K, the corresponding values of relative cooling power and refrigerant capacity are 269 and 214 J/kg, respectively. Particularly, the values of -ΔSMmax reach 11.8 and 19.6 J/kg K for a low field change of 0-1 and 0-2 T, respectively. The present results indicate that TmZn could be a promising candidate for low temperature and low field magnetic refrigeration.

  17. Electric field-induced transport modulation in VO2 FETs with high-k oxide/organic parylene-C hybrid gate dielectric

    Science.gov (United States)

    Wei, Tingting; Kanki, Teruo; Fujiwara, Kohei; Chikanari, Masashi; Tanaka, Hidekazu

    2016-02-01

    We report on the observation of reversible and immediate resistance switching by high-k oxide Ta2O5/organic parylene-C hybrid dielectric-gated VO2 thin films. Resistance change ratios at various temperatures in the insulating regime were demonstrated to occur in the vicinity of phase transition temperature. We also found an asymmetric hole-electron carrier modulation related to the suppression of phase transition temperature. The results in this research provide a possibility for clarifying the origin of metal-insulator transition in VO2 through the electrostatic field-induced transport modulation.

  18. Electric field-induced transport modulation in VO{sub 2} FETs with high-k oxide/organic parylene-C hybrid gate dielectric

    Energy Technology Data Exchange (ETDEWEB)

    Wei, Tingting [Institute of Scientific and Industrial Research, Osaka University, 8-1 Mihogaoka, Ibaraki, Osaka 567-0047 (Japan); Faculty of Science, Kunming University of Science and Technology, Kunming 650093 (China); Kanki, Teruo, E-mail: kanki@sanken.osaka-u.ac.jp, E-mail: h-tanaka@sanken.osaka-u.ac.jp; Chikanari, Masashi; Tanaka, Hidekazu, E-mail: kanki@sanken.osaka-u.ac.jp, E-mail: h-tanaka@sanken.osaka-u.ac.jp [Institute of Scientific and Industrial Research, Osaka University, 8-1 Mihogaoka, Ibaraki, Osaka 567-0047 (Japan); Fujiwara, Kohei [Institute for Materials Research, Tohoku University, Sendai 980-8577 (Japan)

    2016-02-01

    We report on the observation of reversible and immediate resistance switching by high-k oxide Ta{sub 2}O{sub 5}/organic parylene-C hybrid dielectric-gated VO{sub 2} thin films. Resistance change ratios at various temperatures in the insulating regime were demonstrated to occur in the vicinity of phase transition temperature. We also found an asymmetric hole-electron carrier modulation related to the suppression of phase transition temperature. The results in this research provide a possibility for clarifying the origin of metal-insulator transition in VO{sub 2} through the electrostatic field-induced transport modulation.

  19. Electrical properties and electric field-induced antiferroelectric-ferroelectric phase transition in Nd3+-doped lead strontium zirconate titanate ceramics

    Science.gov (United States)

    Yu, Yongjian; Singh, Raj N.

    2003-12-01

    Undoped and 1-3 at. % Nd3+-doped lead strontium zirconate titanate ceramics, which were located near the tetragonal antiferroelectric (AFE) and rhombohedral ferroelectric (FE) phase boundary, were prepared by tape casting and sintering. The influence of the electric field-induced AFE to FE phase transition on the piezoelectric and strain behavior was studied. Attempts were made to increase the field-induced strain by Nd3+ doping and its effect on the dielectric properties. Room temperature resistivity was also measured and explained by the defects produced. An in situ x-ray diffraction technique was developed for direct observation of the unit cell dimensions associated with the field-induced AFE to FE phase transition. The results indicated that a change in unit cell volume was responsible for the large field-induced strain associated with the AFE-FE phase transition.

  20. Temperature- and electric-field-induced inverse Freedericksz transition in a nematogen with weak surface anchoring

    Science.gov (United States)

    Kumar, T. Arun; Sathyanarayana, P.; Sastry, V. S. S.; Takezoe, Hideo; Madhusudana, N. V.; Dhara, Surajit

    2010-07-01

    We report electric field dependence of the anchoring transition in a mesogen on cooling in a cell with perfluoropolymer treated surfaces. Below a crossover voltage Vco the transition is discontinuous between planar and homeotropic alignments, and as the temperature is lowered, the transition temperature decreases quadratically with the field. Above Vco the transition is continuous between planar and tilted alignments, the transition temperature decreasing essentially linearly with the rms field. We develop a simple model to account for these results and argue that the higher field regime corresponds to a temperature driven inverse Freedericksz transition in which the director orientation starts tilting at the weakly anchored surfaces while the tilt angle remains zero at the midplane of the cell.

  1. Millimeter Wave Metal-Insulator-Metal Detector/Mixer Diode.

    Science.gov (United States)

    1983-12-01

    AO-A138 391 MILLIMETER WAVE METAL-INSULATOR- METAL DETECTOR /MIXER 1/1 DIODE(VI NORTH CAROLIN A AGRICULTURAL A NO TECHNI CA L STATE UNIV GREENSRO. C TV...163-A I V AFWAL-TR-83-1179 MILLIMETER WAVE METAL-INSULATOR- METAL DETECTOR /MIXER DIODE CHUNG YU NORTH CAROLINA A&T STATE UNIVERSITY GREENSBORO, NORTH...TITLE (ad subsorle.I S. TYPE CrjflT&PEO OER MILLIMETER WAVE May, 1981--July, 1983 METAL-INSULATOR- METAL DETECTOR /MIXER G. PERFORMING ORG. REPORT

  2. Boundary field induced first-order transition in the 2D Ising model: exact study

    Energy Technology Data Exchange (ETDEWEB)

    Clusel, Maxime [Institut Laue-Langevin, 6 rue Horowitz BP156 X, 38042 Grenoble Cedex (France); Fortin, Jean-Yves [Laboratoire Poncelet, 119002, Bolshoy Vlasyevskiy Pereulok 11, Moscow (Russian Federation)

    2006-02-03

    We present in this paper an exact study of a first-order transition induced by an inhomogeneous boundary magnetic field in the 2D Ising model. From a previous analysis of the interfacial free energy in the discrete case (Clusel and Fortin 2005 J. Phys. A: Math. Gen. 38 2849) we identify, using an asymptotic expansion in the thermodynamic limit, the line of transition that separates the regime where the interface is localized near the boundary from the one where it is propagating inside the bulk. In particular, the transition line has a strong dependence on the aspect ratio of the lattice.

  3. Electric Field-induced Conformational Transition of Bovine Serum Albumin from α -helix to β -sheet

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    The irreversible conformational transition of bovine serum albumin (BSA) from α -helix to β -sheet, induced by electric field near the electrode surface, was monitored by circular dichroism (CD) with a long optical path thin layer cell (LOPTLC).

  4. A boundary field induced first-order transition in the 2D Ising model: numerical study

    Energy Technology Data Exchange (ETDEWEB)

    Bittner, Elmar; Janke, Wolfhard [Institut fuer Theoretische Physik and Centre for Theoretical Sciences (NTZ), Universitaet Leipzig, Postfach 100 920, D-04009 Leipzig (Germany)], E-mail: elmar.bittner@itp.uni-leipzig.de, E-mail: Wolfhard.janke@itp.uni-leipzig.de

    2008-10-03

    In a recent paper, Clusel and Fortin (2006 J. Phys. A: Math. Gen. 39 995) presented an analytical study of a first-order transition induced by an inhomogeneous boundary magnetic field in the two-dimensional Ising model. They identified the transition that separates the regime where the interface is localized near the boundary from that where it propagates inside the bulk. Inspired by these results, we measured the interface tension by using multimagnetic simulations combined with parallel tempering to determine the phase transition and the location of the interface. Our results are in very good agreement with the theoretical predictions. Furthermore, we studied the spin-spin correlation function for which no analytical results are available.

  5. Cascade of magnetic field induced spin transitions in LaCoO3.

    Science.gov (United States)

    Altarawneh, M M; Chern, G-W; Harrison, N; Batista, C D; Uchida, A; Jaime, M; Rickel, D G; Crooker, S A; Mielke, C H; Betts, J B; Mitchell, J F; Hoch, M J R

    2012-07-20

    We present magnetization and magnetostriction studies of LaCoO3 in magnetic fields approaching 100 T. In contrast with expectations from single-ion models, the data reveal two distinct first-order transitions and well-defined magnetization plateaus. The magnetization at the higher plateau is only about half the saturation value expected for spin-1 Co3+ ions. These findings strongly suggest collective behavior induced by interactions between different electronic configurations of Co3+ ions. We propose a model that predicts crystalline spin textures and a cascade of four magnetic phase transitions at high fields, of which the first two account for the experimental data.

  6. Quantum-classical correspondence of a field induced KAM-type transition: A QTM approach

    Indian Academy of Sciences (India)

    P K Chattaraj; S Sengupta; S Giri

    2008-01-01

    A transition from regular to chaotic behaviour in the dynamics of a classical Henon-Heiles oscillator in the presence of an external field is shown to have a similar quantum signature when studied using the pertaining phase portraits and the associated Kolmogorov-Sinai-Lyapunov entropies obtained through the corresponding Bohmian trajectories.

  7. Magnetic field-induced charge-density-wave transitions: The role of the orbital and Pauli effects

    Science.gov (United States)

    Kartsovnik, M. V.; Andres, D.; Biberacher, W.; Müller, H.

    2009-03-01

    Due to a low transition temperature and, correspondingly, a small energy gap, the charge-density-wave (CDW) state of the layered organic metal α-(BEDT-TTF)2KHg(SCN)4 is very sensitive to pressure and magnetic field. The latter couples to the CDW via two competing mechanisms: Pauli paramagnetism and orbital motion of charge carriers in a magnetic field. We study the interplay between the Pauli and orbital effects under a pressure of 2.8 kbar, in the region of the field-induced CDW (FICDW) instability. We find that, in agreement with theoretical predictions, the FICDW state is enhanced when the Zeeman splitting becomes commensurate with the orbital quantization.

  8. Magnetic field-induced charge-density-wave transitions: The role of the orbital and Pauli effects

    Energy Technology Data Exchange (ETDEWEB)

    Kartsovnik, M.V. [Walther-Meissner-Institut, Bayerische Akademie der Wissenschaften, 85748 Garching (Germany)], E-mail: mark.kartsovnik@wmi.badw.de; Andres, D.; Biberacher, W. [Walther-Meissner-Institut, Bayerische Akademie der Wissenschaften, 85748 Garching (Germany); Mueller, H. [European Synchrotron Radiation Facility, F-38043 Grenoble (France)

    2009-03-01

    Due to a low transition temperature and, correspondingly, a small energy gap, the charge-density-wave (CDW) state of the layered organic metal {alpha}-(BEDT-TTF){sub 2}KHg(SCN){sub 4} is very sensitive to pressure and magnetic field. The latter couples to the CDW via two competing mechanisms: Pauli paramagnetism and orbital motion of charge carriers in a magnetic field. We study the interplay between the Pauli and orbital effects under a pressure of 2.8 kbar, in the region of the field-induced CDW (FICDW) instability. We find that, in agreement with theoretical predictions, the FICDW state is enhanced when the Zeeman splitting becomes commensurate with the orbital quantization.

  9. Electric field induced phase transitions in polymers: a novel mechanism for high speed energy storage.

    Science.gov (United States)

    Ranjan, V; Nardelli, Marco Buongiorno; Bernholc, J

    2012-02-24

    Using first-principles simulations, we identify the microscopic origin of the nonlinear dielectric response and high energy density of polyvinylidene-fluoride-based polymers as a cooperative transition path that connects nonpolar and polar phases of the system. This path explores a complex torsional and rotational manifold and is thermodynamically and kinetically accessible at relatively low temperatures. Furthermore, the introduction of suitable copolymers significantly alters the energy barriers between phases providing tunability of both the energy density and the critical fields.

  10. Exciton states in a circular graphene quantum dot: Magnetic field induced intravalley to intervalley transition

    Science.gov (United States)

    Li, L. L.; Zarenia, M.; Xu, W.; Dong, H. M.; Peeters, F. M.

    2017-01-01

    The magnetic-field dependence of the energy spectrum, wave function, binding energy, and oscillator strength of exciton states confined in a circular graphene quantum dot (CGQD) is obtained within the configuration interaction method. We predict that (i) excitonic effects are very significant in the CGQD as a consequence of a combination of geometric confinement, magnetic confinement, and reduced screening; (ii) two types of excitons (intravalley and intervalley) are present in the CGQD because of the valley degree of freedom in graphene; (iii) the intravalley and intervalley exciton states display different magnetic-field dependencies due to the different electron-hole symmetries of the single-particle energy spectra; (iv) with increasing magnetic field, the exciton ground state in the CGQD undergoes an intravalley to intervalley transition accompanied by a change of angular momentum; (v) the exciton binding energy does not increase monotonically with the magnetic field due to the competition between geometric and magnetic confinements; and (vi) the optical transitions of the intervalley and intravalley excitons can be tuned by the magnetic field, and valley-dependent excitonic transitions can be realized in a CGQD.

  11. Multipartite non-locality and entanglement signatures of a field-induced quantum phase transition

    Science.gov (United States)

    Batle, Josep; Alkhambashi, Majid; Farouk, Ahmed; Naseri, Mosayeb; Ghoranneviss, Mahmood

    2017-02-01

    Quantum correlation measures are limited in practice to a few number of parties, since no general theory is still capable of reaching the thermodynamic limit. In the present work we study entanglement and non-locality for a cluster of spins belonging to a compound that displays a magnetocaloric effect. A quantum phase transition (QPT) is induced by an external magnetic field B, in such a way that the corresponding quantum fluctuations are reproduced at a much smaller scale than the experimental outcomes, and then described by means of the aforementioned quantum measures.

  12. Internal field induced exciton binding energy and the optical transition in a strained Mg based II–VI quantum well

    Energy Technology Data Exchange (ETDEWEB)

    Elangovan, P. [Department of Physics, Maamallan Institute of Technology, Chennai 602105 (India); John Peter, A., E-mail: a.john.peter@gmail.com [Department of Physics, Government Arts College, Melur 625 106. Madurai (India); Kyoo Yoo, Chang [Center for Environmental Studies/Green Energy Center, Deptartment of Environmental Science and Engineering, College of Engineering, Kyung Hee University, Seocheon-dong 1, Giheung-gu, Yongin-Si, Gyeonggi-Do, 446-701 (Korea, Republic of)

    2013-11-15

    Binding energy of an exciton in a wurtzite ZnO/Zn{sub 1−x}Mg{sub x}O strained quantum well is investigated theoretically in which the strong built-in electric field due to the spontaneous and piezoelectric polarizations is included. Numerical calculations are performed using variational procedure within the single band effective mass approximation by varying the Mg composition in the barrier. The exciton oscillator strength and the exciton lifetime for radiative recombination as functions of well width and Mg content have been computed. The internal field induced interband emission energy of strained ZnO/Zn{sub 1−x}Mg{sub x}O well is investigated with the various structural parameters. The total optical absorption coefficients and the changes of refractive index as a function of normalized photon energy in the presence of built-in internal field are analyzed. The result shows that the strong built-in electric field has influence on the oscillator strength and the recombination life time of the exciton. The optical absorption coefficients and the refractive index changes strongly depend on Mg composition. The occurred blue shift of the resonant peak due to the incorporation of Mg ions will give the information about the variation of two energy levels in the quantum well. -- Highlights: • Binding energy of an exciton in a wurtzite ZnO/Zn{sub 1−x}Mg{sub x}O strained quantum well is investigated. • The built-in internal fields due to the spontaneous and piezoelectric polarizations are included. • The oscillator strength and the exciton lifetime for radiative recombination are computed. • The internal field induced transition energy of strained ZnO/Zn{sub 1−x}Mg{sub x}O well is investigated. • The results show that the nonlinear optical properties strongly depend on Mg composition.

  13. AC-field-induced quantum phase transitions in density of states

    Science.gov (United States)

    Yang, Kai-Hua; Liu, Kai-Di; Wang, Huai-Yu; Qin, Chang-Dong

    2016-02-01

    We investigate the joint effects of the intralead electron interaction and an external alternating gate voltage on the time-averaged local density of states (DOSs) of a quantum dot coupled to two Luttinger-liquid leads in the Kondo regime. A rich dependence of the DOSs on the driving amplitude and intralead interaction is demonstrated. We show that the feature is quite different for different interaction strengths in the presence of the ac field. It is shown that the photon-assisted transport processes cause an additional splitting of the Kondo peak or dip, which exhibits photon-assisted single-channel (1CK) or two-channel Kondo (2CK) physics behavior. The phase transition between photon-assisted 1CK and 2CK physics occurs when the interaction strength is moderately strong. The inelastic channels associated with photon-assisted electron tunneling can dominate electron transport for weak interaction when the ac amplitude is greater than the frequency by one order of magnitude. In the limit of strong interaction the DOSs scale as a power-law behavior which is strongly affected by the ac field.

  14. Quantum Magnetic Oscillations of the Surface Tension at a Metal-Insulator Interface

    Science.gov (United States)

    Dubovskii, L. B.

    2016-03-01

    Any metal-insulator transition (MI transition) in a crystalline material must be a transition from a situation in which electronic bands overlap to a situation when they do not (Mott, Metal-insulator, 2nd edn. Taylor@Francis, London, 1990). For this case the self-consistent equations for the two-band conductor are formulated (cf. Dubovskii, JETP Lett. 99(1):22-26, 2014). The description of the MI phase transition is based on two order parameters. The first one is the material density distribution at the MI boundary ρ ({vec {r}}). The second one is a four-component complex vector in spin space Upsilon ({vec {r}}). The value Upsilon ({vec {r}}) determines the electron density in the metallic or semimetallic phase in the presence of an external magnetic field. Two different components of the vector describe possible spin states of electrons and holes inserted in the external magnetic field. The solution gives a singular behavior of the surface tension at the MI interface in the vicinity of the MI phase transition. At low temperature quantum oscillations of the surface tension in the magnetic field take place.

  15. Field-Induced Multiple Reentrant Quantum Phase Transitions in Randomly Dimerized Antiferromagnetic S=1/2 Heisenberg Chains

    Science.gov (United States)

    Hida, Kazuo

    2006-07-01

    The multiple reentrant quantum phase transitions in the S=1/2 antiferromagnetic Heisenberg chains with random bond alternation in the magnetic field are investigated by the density matrix renormalization group method combined with interchain mean field approximation. It is assumed that odd numbered bonds are antiferromagnetic with strength J and even numbered bonds can take the values JS and JW (JS > J > JW > 0) randomly with the probabilities p and 1- p, respectively. The pure version ( p=0 and 1) of this model has a spin gap but exhibits a field-induced antiferromagnetism in the presence of interchain coupling if Zeeman energy due to the magnetic field exceeds the spin gap. For 0 < p < 1, antiferromagnetism is induced by randomness at the small field region where the ground state is disordered due to the spin gap in the pure version. At the same time, this model exhibits randomness-induced plateaus at several values of magnetization. The antiferromagnetism is destroyed on the plateaus. As a consequence, we find a series of reentrant quantum phase transitions between transverse antiferromagnetic phases and disordered plateau phases with the increase of magnetic field for a moderate strength of interchain coupling. Above the main plateaus, the magnetization curve consists of a series of small plateaus and jumps between them. It is also found that antiferromagnetism is induced by infinitesimal interchain coupling at the jumps between the small plateaus. We conclude that this antiferromagnetism is supported by the mixing of low-lying excited states by the staggered interchain mean field even though the spin correlation function is short ranged in the ground state of each chain.

  16. Charging damage in floating metal-insulator-metal capacitors

    NARCIS (Netherlands)

    Ackaert, Jan; Wang, Zhichun; De Backer, E.; Coppens, P.

    2002-01-01

    In this paper, charging induced damage (CID) to metal-insulator-metal capacitors (MIMC) is reported. The damage is caused by the build up of a voltage potential difference between the two plates of the capacitor. A simple logarithmic relation is discovered between the damage by this voltage potentia

  17. LDA+DMFT study of metal-insulator transition in the bulk and at the surface of Ca{sub x}Sr{sub 2-x}RuO{sub 4}

    Energy Technology Data Exchange (ETDEWEB)

    Karolak, Michael; Wehling, Tim; Lechermann, Frank; Lichtenstein, Alexander [I. Institut fuer Theoretische Physik, Universitaet Hamburg, Jungiusstrasse 9, 20355 Hamburg (Germany)

    2009-07-01

    Ca{sub x}Sr{sub 2-x}RuO{sub 4} is an interesting model system to study the interplay of structural distortions and the electronic metal to insulator transition. We present an ab-initio study within the LDA+DMFT framework of this system. In this way we account for changes in the one particle Hamiltonian due to the structural distortions in a first principles manner. We obtain the electronic density of states and the self energy. The mechanism of the metal to insulator transition in the bulk and at the surface of this system is discussed. A strong enhancement of electron correlation effects is found for the low temperature structures.

  18. Field-induced charge-density-wave transitions in the organic metal α-(BEDT-TTF)2KHg(SCN)4 under pressure

    Science.gov (United States)

    Andres, D.; Kartsovnik, M. V.; Biberacher, W.; Neumaier, K.; Sheikin, I.; Müller, H.; Kushch, N. D.

    2011-10-01

    Successive magnetic-field-induced charge-density-wave transitions in the layered molecular conductor α-(BEDT-TTF)2KHg(SCN)4 are studied in a hydrostatic pressure regime in which the zero field charge-density- wave (CDW) state is completely suppressed. It is shown that the orbital effect of the magnetic field restores the density wave, while orbital quantization induces transitions between different CDW states as the field strength is varied. The latter show up as distinct anomalies in the magnetoresistance as a function of field. The interplay between the orbital and Pauli paramagnetic effects, which act, respectively, to enhance and to suppress the CDW instability, is particularly manifest in the angular dependence of the field-induced anomalies.

  19. Carrier tuning the metal-insulator transition of epitaxial La0.67Sr0.33MnO3 thin film on Nb doped SrTiO3 substrate

    Directory of Open Access Journals (Sweden)

    J. M. Zhan

    2016-04-01

    Full Text Available La0.67Sr0.33MnO3 (LSMO thin films were deposited on (001SrTiO3(STO and n-type doped Nb:SrTiO3(NSTO single crystal substrates respectively. The metal to insulator transition temperature(TMI of LSMO film on NSTO is lower than that on STO, and the TMI of LSMO can be tuned by changing the applied current in the LSMO/NSTO p-n junction. Such behaviors were considered to be related to the carrier concentration redistribution in LSMO film caused by the change of depletion layer thickness in p-n junction which depends greatly on the applied electric field. The phenomenon could be used to configure artificial devices and exploring the underlying physics.

  20. A first-order magnetic phase transition near 15 K with novel magnetic-field-induced effects in Er5Si3.

    Science.gov (United States)

    Mohapatra, Niharika; Mukherjee, K; Iyer, Kartik K; Sampathkumaran, E V

    2011-12-14

    We present magnetic characterization of a binary rare-earth intermetallic compound Er(5)Si(3), crystallizing in Mn(5)Si(3)-type hexagonal structure, through magnetization, heat capacity, electrical resistivity and magnetoresistance measurements. Our investigations confirm that the compound exhibits two magnetic transitions with decreasing temperature, the first one at 35 K and the second one at 15 K. The present results reveal that the second magnetic transition is a disorder-broadened first-order transition, as shown by thermal hysteresis in the measured data. Another important finding is that, below 15 K, there is a magnetic-field-induced transition with a hysteretic effect with the electrical resistance getting unusually enhanced at this transition and the magnetoresistance is found to exhibit intriguing magnetic-field dependence, indicating novel magnetic phase coexistence phenomenon. It thus appears that this compound is characterized by interesting magnetic anomalies in the temperature-magnetic-field phase diagram.

  1. A Difference in Using Atomic Layer Deposition or Physical Vapour Deposition TiN as Electrode Material in Metal-Insulator-Metal and Metal-Insulator-Silicon Capacitors

    NARCIS (Netherlands)

    Groenland, A.W.; Wolters, R.A.M.; Kovalgin, A.Y.; Schmitz, J.

    2011-01-01

    In this work, metal-insulator-metal (MIM) and metal-insulator-silicon (MIS) capacitors are studied using titanium nitride (TiN) as the electrode material. The effect of structural defects on the electrical properties on MIS and MIM capacitors is studied for various electrode configurations. In the M

  2. Isotropic-Cholesteric Co-Existence and Magnetic Field-Induced Isotropic-Nematic Transition of Filamentous Bacteriophage FD in Aqueous Suspension.

    Science.gov (United States)

    Tang, Jianxin

    1995-01-01

    Isotropic to liquid crystalline phase transition for a lyotropic suspension of geometrically asymmetric macromolecules occurs to a wild class of synthetic polymers and biopolymers. Although in decades statistical mechanical theories have been developed to predict the thermodynamic conditions and the properties of such transition, quantitative comparison with theory has been compounded with complications such as charge, shape, polydispersity in size, and additional interactions with the solvent and among the macromolecules themselves. We chose the aqueous suspension of the filamentous bacteriophage fd as a model system to study the isotropic to liquid crystalline transition. The co-existence concentrations, as a function of ionic strength, were measured directly by spectrophotometry. Our data confirm quantitatively the predictions of a statistical mechanic treatment first described by Onsager, modified to include the effects of charge and flexibility of rodlike particles. We have also extended a previous study of the pretransitional angular correlations in the isotropic solutions of fd through the measurement of the magnetic-field-induced birefringence, i.e. the measurement of the Cotton-Mouton constant. At several ionic strengths the magnetic-field-induced birefringence, which is proportional to the number of particles in a correlation volume N_{rm corr}, was measured for fd concentrations spanning the entire isotropic region. From this data the limiting concentration of stability (spinodal) of the isotropic phase is obtained. A theoretical expression for the magnetic birefringence of persistent polymers was derived and agreed well with the data with the exception that N_{rm corr} at the isotropic to liquid crystal transition was smaller than predicted. In the proximity of the highest possible isotropic concentration, that is the isotropic in co-existence with anisotropic, we studied the effect of a high magnetic field. A first order field-induced isotropic

  3. METAL-INSULATOR TRANSITIONS AND STRONG ELECTRON CORRELATIONS

    NARCIS (Netherlands)

    MICHIELSEN, K

    1993-01-01

    An overview of lattice models for strongly correlated electrons is given. A detailed study is presented of a model recently introduced by Montorsi and Rasetti. Analytical, exact diagonalization and Quantum Monte Carlo techniques are employed to investigate the static and dynamic properties of this m

  4. Magnetic-field-induced first-order phase transitions in Ca3(Ru1-xFex)2 O7 with unusual irreversible behaviors

    Science.gov (United States)

    Zhu, Mengze; Peng, Jin; Zou, Tao; Hong, Tao; Prokes, Karel; Mahanti, S. D.; Mao, Zhiqiang; Ke, Xianglin

    Neutron diffraction measurements reveal a magnetic-field-induced incommensurate-commensurate magnetic structure transition in a bilayer ruthenate Ca3(Ru1-xFex)2 O7 (x = 0.05). The transition is of first-order in nature, and exhibits intriguing irreversible behaviors at low temperature, i.e. the zero-field incommensurate state before and after field sweeping showing very distinct magnetic ordering wave vectors. The difference in the wavelength of magnetic ordering is strongly temperature-dependent, and disappears gradually as temperature raises. This unusual irreversibility in magnetic ordering vector is rarely observed, and in disagreement with phase coexistence phenomena that is commonly seen in other irreversible first-order phase transitions. Nevertheless, our results demonstrate that thermal fluctuations also play an essential role in this unusual behavior.

  5. Enhanced rectifying response from metal-insulator-insulator-metal junctions

    Science.gov (United States)

    Maraghechi, P.; Foroughi-Abari, A.; Cadien, K.; Elezzabi, A. Y.

    2011-12-01

    We present on a metal-insulator-insulator-metal quantum electronic tunneling devices suitable for high speed rectifiers. Through the introduction of double oxide layer between similar metallic electrodes, a cascaded potential barrier is formed which alters the electron tunneling mechanism at forward versus the reverse bias. The cascaded potential barrier engineering manifests itself in both a highly nonlinear and asymmetric I-V junction characteristic. It is envisioned that high speed rectifiers and mixers having extraordinary nonlinearity can be realized through the incorporation of the cascaded potential barrier architecture and dissimilar metallic electrodes.

  6. Ultracompact plasmonic racetrack resonators in metal-insulator-metal waveguides

    CERN Document Server

    Han, Zhanghua

    2010-01-01

    Among various plasmonic waveguides, the metal-insulator-metal (MIM) type is the most promising for true subwavelength photonic integration. To date, many photonic devices based on MIM waveguides have been investigated, including resonators. However, most of the reported MIM ring resonators suffer from low extinction ratios. In this paper, we present a comprehensive analysis of the intrinsic reasons for the low performance of MIM ring resonators, and give the analytical transmission relation for a universal all-pass ring resonator which has coupling loss. Based on the analysis we propose the plasmonic racetrack resonators in MIM waveguides and show that the performance can be greatly improved.

  7. Tunneling Conductance in Normal Metal/Insulator/Triplet Superconductor Junction

    Institute of Scientific and Technical Information of China (English)

    LI Xiao-Wei

    2005-01-01

    Tunneling conductance in normal metal/insulator/triplet superconductor junctions is studied theoretically as a function of the bias voltage at zero temperature and finite temperature. The results show there are zero-bias conductance peak, zero-bias conductance dip and double-minimum structures in the spectra for p-wave superconductor junctions. The existence of such structures in the conductance spectrum can be taken as evidence that the pairing symmetry of Sr2RuO4 is p-wave symmetry.

  8. Magnetic field-induced quantum superconductor-insulator transition in $Nb_{0.15}Si_{0.85}$

    OpenAIRE

    Aubin, H.; Marrache-Kikuchi, C. A.; Pourret, A.; Behnia, K.; Berge, L.; Dumoulin, L.; Lesueur, J.

    2006-01-01

    A study of magnetic-field tuned superconductor-insulator transitions in amorphous $Nb_{0.15}Si_{0.85}$ thin films shows that quantum superconductor-insulator transitions are characterized by an unambiguous signature -- a kink in the temperature profile of the critical magnetic field. Using this criterion, we show that the nature of the magnetic-field tuned superconductor-insulator transition depends on the orientation of the field with respect to the film. For perpendicular magnetic field, th...

  9. Electric field-induced phase transitions in Li-modified Na{sub 0.5}K{sub 0.5}NbO{sub 3} at the polymorphic phase boundary

    Energy Technology Data Exchange (ETDEWEB)

    Iamsasri, Thanakorn; Jones, Jacob L., E-mail: jacobjones@ncsu.edu [Department of Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina 27695 (United States); Department of Materials Science and Engineering, University of Florida, Gainesville, Florida 32611 (United States); Tutuncu, Goknur [Department of Materials Science and Engineering, University of Florida, Gainesville, Florida 32611 (United States); Uthaisar, Chunmanus; Pojprapai, Soodkhet [School of Ceramic Engineering, Institute of Engineering, Suranaree University of Technology, Nakorn Ratchasima 30000 (Thailand); Wongsaenmai, Supattra [Program in Materials Science, Faculty of Science, Maejo University, Chiang Mai 50290 (Thailand)

    2015-01-14

    The electric field-induced phase transitions in Li-modified Na{sub 0.5}K{sub 0.5}NbO{sub 3} at the polymorphic phase boundary (PPB) were observed using in situ X-ray diffraction. The ratio of monoclinic to tetragonal phase fraction was used as an indicator of the extent and reversibility of the phase transitions. The reversibility of the phase transition was greater in compositions further from the PPB. These results demonstrate that the field-induced phase transition is one of the origins of high piezoelectric properties in lead-free ferroelectric materials.

  10. Metal-insulator-metal waveguides for particle trapping and separation.

    Science.gov (United States)

    Khan, Saara A; Chang, Chia-Ming; Zaidi, Zain; Shin, Wonseok; Shi, Yu; Ellerbee Bowden, Audrey K; Solgaard, Olav

    2016-06-21

    Optical particle trapping and separation are essential techniques in the fields of biology and chemistry. In many applications, it is important to identify passive separation techniques that only rely on intrinsic forces in a system with a fixed device geometry. We present a dual-waveguide sorter that utilizes the loss of metal-insulator-metal (MIM) waveguides for completely passive particle trapping and separation and is created using a unique angle sidewall deposition process. Our experiments show that an inner Au-Si3N4-Au waveguide is able to trap particles within the propagation distance of its dominant modes and release the particles into an outer Au-H2O-Au waveguide. The outer waveguide then propels the particles and separates them by size. The separation results are accurately modeled by a first-principles, analytical model.

  11. Metal-Insulator-Semiconductor Nanowire Network Solar Cells.

    Science.gov (United States)

    Oener, Sebastian Z; van de Groep, Jorik; Macco, Bart; Bronsveld, Paula C P; Kessels, W M M; Polman, Albert; Garnett, Erik C

    2016-06-08

    Metal-insulator-semiconductor (MIS) junctions provide the charge separating properties of Schottky junctions while circumventing the direct and detrimental contact of the metal with the semiconductor. A passivating and tunnel dielectric is used as a separation layer to reduce carrier recombination and remove Fermi level pinning. When applied to solar cells, these junctions result in two main advantages over traditional p-n-junction solar cells: a highly simplified fabrication process and excellent passivation properties and hence high open-circuit voltages. However, one major drawback of metal-insulator-semiconductor solar cells is that a continuous metal layer is needed to form a junction at the surface of the silicon, which decreases the optical transmittance and hence short-circuit current density. The decrease of transmittance with increasing metal coverage, however, can be overcome by nanoscale structures. Nanowire networks exhibit precisely the properties that are required for MIS solar cells: closely spaced and conductive metal wires to induce an inversion layer for homogeneous charge carrier extraction and simultaneously a high optical transparency. We experimentally demonstrate the nanowire MIS concept by using it to make silicon solar cells with a measured energy conversion efficiency of 7% (∼11% after correction), an effective open-circuit voltage (Voc) of 560 mV and estimated short-circuit current density (Jsc) of 33 mA/cm(2). Furthermore, we show that the metal nanowire network can serve additionally as an etch mask to pattern inverted nanopyramids, decreasing the reflectivity substantially from 36% to ∼4%. Our extensive analysis points out a path toward nanowire based MIS solar cells that exhibit both high Voc and Jsc values.

  12. Magnetic field induced phase branches of the superconducting transition in two-dimensional square Π-loop arrays

    Institute of Scientific and Technical Information of China (English)

    Liu Dang-Ting; Tian Ye; Chen Geng-Hua; Yang Qian-Sheng

    2008-01-01

    Based on the results of explicit forms of free energy density for each possible arrangement of magnetization fluxes in large-scale two-dimensional (2D) square Π-loop arrays given by Li et al [2007 Chin.Phys.16 1450],the field-cooled superconducting phase transition is further investigated by analysing the free energy of the arrays with a simplified symmetrical model.Our analytical result is exactly the same as that obtained in Li's paper by means of numerical calculations.It is shown that the phase transition splits into two branches with either ferromagnetic or anti-ferromagnetic flux ordering,which depends periodically on the strength of external magnetic flux φe through each loop and monotonically on the screen parameter β of the loops in the arrays.In principle,the diagram of the phase branches is similar to that of its one-dimensional counterpart.The influence of thermal fluctuation on the flux ordering during the transition from normal to superconducting states of the Π-loop arrays is also discussed.

  13. Electric field induced transition between spin to valley polarized ν = 0 quantum Hall state in dual-gated graphene bilayers

    Science.gov (United States)

    Lee, Kayoung; Kim, Seyoung; Fallahazad, Babak; Tutuc, Emanuel

    2011-03-01

    Graphene bilayers in Bernal stacking exhibit a transverse electric field dependent energy gap, thanks to the on-site electron energy asymmetry between the two layers. In a perpendicular magnetic field, the applied transverse electric field (E) will induce a quantum Hall state (QHS) at the charge neutrality point (filling factor ν = 0) marked by a insulating behavior of the longitudinal resistance (ρxx) , and a plateau in the Hall conductivity. Using dual-gated graphene bilayers, we investigate here the E -field dependence of the ν = 0 QHS in high perpendicular magnetic fields (B) , up to 30T. The temperature dependence of ρxx measured at ν = 0 shows an insulating behavior, which is strongest in the vicinity of E = 0 as well as at large E -fields. At a fixed B -field, as a function of the applied E -field the ν = 0 QHS undergoes a transition, marked by a ρxx minimum, as well as a temperature independent ρxx at a finite E -field value. This observation can be explained by a transition from a spin polarized ν = 0 QHS at small E -fields, to a valley (layer) polarized ν = 0 QHS at large E -fields. The E -field value at which the transition occurs follows a linear dependence on the applied perpendicular magnetic field, with a slope of ~ 18 mV/ nm . T. We thank NRI and NSF for support.

  14. Field-Induced Spin-State Transition in LaCo1-xMxO3 (M = Al, Ga, Rh, and Ir)

    Science.gov (United States)

    Sato, Keisuke; Matsuo, Akira; Kindo, Koichi; Hara, Yoshiaki; Nakaoka, Kanichiro; Kobayashi, Yoshihiko; Asai, Kichizo

    2014-11-01

    We have investigated the high-field magnetization of lightly doped LaCo1-xMxO3 with M = Al, Ga, Rh, and Ir up to 67 T. The transition field for the field-induced spin-state transition at 4.2 K, which is μ0Hc = 60 T in LaCoO3, increases slightly for M = Al but does not change for M = Ga. On the other hand, the transition field decreases remarkably for M = Rh and Ir. The substitution effect on μ0Hc has been interpreted as arising from the lattice-volume dependence of the excitation energy ΔI of CoI from the low-spin (LS) to high-spin (HS) state. The fraction of CoI is 15% of the total number of Co ions. The remaining Co ions, CoII, are excited from the LS to intermediate-spin (IS) state and contribute to the magnetization at high temperatures above 100 K. We propose the coexistence of the HS and IS states in LaCo1-xMxO3. For M = Rh and Ir, Co species with the magnetic ground state, CoIII, are populated by their substitution. The formation mechanism and spin states of CoIII are discussed in comparison with those of the magnetic Co species in La1-xSrxCoO3.

  15. Electronic structure of UN based on specific heat and field-induced transitions up to 65 T

    Science.gov (United States)

    Troć, R.; Samsel-Czekała, M.; Pikul, A.; Andreev, A. V.; Gorbunov, D. I.; Skourski, Y.; Sznajd, J.

    2016-12-01

    The 5 f electrons of uranium in the uranium mononitride (UN) compound are described in the literature as either localized or fully itinerant. Motivated by these contradictory statements, we studied low-temperature specific heat and high-field magnetization of single-crystalline UN in magnetic fields up to 9 and 65 T, respectively. Our detailed analysis of the magnetic contribution to the specific heat of UN revealed that its real ground state is complex and the 5 f electrons seem to have a dual nature; i.e., they possess simultaneously local and itinerant characters in two substates. High-field experiments allowed us to construct a tentative magnetic phase diagram of UN with a metamagnetic transition from antiferromagnetism to ferrimagnetism at a magnetic field as high as 58 T at 2 K. Such a field only enables a reversal of 1 of the 12 antiferromagnetically coupled ferromagnetic layers in the direction of the magnetic field. Any further steplike transitions require application of ever higher magnetic fields, which is beyond the experimental possibilities. We show that the magnetic phase diagram can be successfully reproduced considering a layer model of the Ising spins. That model allows rough estimation of a phase transition into fully induced ferromagnetism at a field as high as about 258 T. It gives rise to a giant coupling between ferromagnetically ordered layers in UN. The obtained characteristics are presented, together with the results of recent x-ray photoemission spectroscopy and transport property measurements. They are analyzed and compared with a number of earlier experiments and band structure calculations that were performed for this compound and are widely described in the literature. We show that different experiments probe different substates of the uranium 5 f electrons in UN (itinerant or localized), which supports our hypothesis on their dual nature.

  16. Magnetic-field-induced vortex-lattice transition in HgBa2CuO4 +δ

    Science.gov (United States)

    Lee, Jeongseop A.; Xin, Yizhou; Stolt, I.; Halperin, W. P.; Reyes, A. P.; Kuhns, P. L.; Chan, M. K.

    2017-01-01

    Measurements of the 17O nuclear magnetic resonance (NMR) quadrupolar spectrum of apical oxygen in HgBa2CuO4 +δ were performed over a range of magnetic fields from 6.4-30 T in the superconducting state. Oxygen-isotope-exchanged single crystals were investigated with doping corresponding to superconducting transition temperatures from 74 K underdoped, to 78 K overdoped. The apical oxygen site was chosen since its NMR spectrum has narrow quadrupolar satellites that are well separated from any other resonance. Nonvortex contributions to the spectra can be deconvolved in the time domain to determine the local magnetic field distribution from the vortices. Numerical analysis using Brandt's Ginzburg-Landau theory was used to find structural parameters of the vortex lattice, penetration depth, and coherence length as a function of magnetic field in the vortex solid phase. From this analysis we report a vortex structural transition near 15 T from an oblique lattice with an opening angle of 73∘ at low magnetic fields to a triangular lattice with 60∘ stabilized at high field. The temperature for onset of vortex dynamics has been identified from spin-spin relaxation. This is independent of the magnetic field at sufficiently high magnetic field similar to that reported for YBa2Cu3O7 and Bi2Sr2CaCu2O8 +δ and is correlated with mass anisotropy of the material. This behavior is accounted for theoretically only in the limit of very high anisotropy.

  17. Field-Induced Quantum Phase Transitions in S = 1/2 J1-J2 Heisenberg Model on Square Lattice

    Science.gov (United States)

    Morita, Katsuhiro; Shibata, Naokazu

    2016-09-01

    We study the magnetic field dependence of the ground state of the S = 1/2 J1-J2 Heisenberg model on the square lattice by the density matrix renormalization group (DMRG) method. With the use of the sine-square deformation, we obtain eight different ground states including plaquette valence-bond crystal with a finite spin gap, transverse Néel, transverse stripe, 1/2 magnetization plateau with up-up-up-down (uuud), and three new states we named the Y-like, V-like, and Ψ states around J2/J1 = 0.55-0.6. The phase transitions from the transverse Néel (at J2/J1 = 0.55) and stripe (at J2/J1 = 0.6) states to the uuud and Y-like states, respectively, are discontinuous, as in the case of a spin flop.

  18. Magnetic field-induced spectroscopy of forbidden optical transitions with application to lattice-based optical atomic clocks.

    Science.gov (United States)

    Taichenachev, A V; Yudin, V I; Oates, C W; Hoyt, C W; Barber, Z W; Hollberg, L

    2006-03-01

    We develop a method of spectroscopy that uses a weak static magnetic field to enable direct optical excitation of forbidden electric-dipole transitions that are otherwise prohibitively weak. The power of this scheme is demonstrated using the important application of optical atomic clocks based on neutral atoms confined to an optical lattice. The simple experimental implementation of this method--a single clock laser combined with a dc magnetic field--relaxes stringent requirements in current lattice-based clocks (e.g., magnetic field shielding and light polarization), and could therefore expedite the realization of the extraordinary performance level predicted for these clocks. We estimate that a clock using alkaline-earth-like atoms such as Yb could achieve a fractional frequency uncertainty of well below 10(-17) for the metrologically preferred even isotopes.

  19. Electric field-induced suppression of PTEN drives epithelial-to-mesenchymal transition via mTORC1 activation.

    Science.gov (United States)

    Yan, Tiantian; Jiang, Xupin; Guo, Xiaowei; Chen, Wen; Tang, Di; Zhang, Junhui; Zhang, Xingyue; Zhang, Dongxia; Zhang, Qiong; Jia, Jiezhi; Huang, Yuesheng

    2017-02-01

    Naturally occurring electric fields (EFs) are an intrinsic property of wounds. Endogenous EFs in skin wounds play critical roles in the dynamic and well-ordered biological process of wound healing. The epithelial-to-mesenchymal transition (EMT) allows keratinocytes to transition from sedentary cells to motile cells, facilitating wound healing. However, EMT-related studies have been performed without considering endogenous EFs. Thus, the relationship between electrical signals and the EMT remain elusive. Phosphatase and tension homolog (PTEN) and mammalian target of rapamycin complex 1 (mTORC1) are key molecules in sensing electrical cues, and they play significant roles in cellular responses to EFs. In addition, these molecules are closely related to the occurrence of the EMT in other cells. We used primary human keratinocytes to investigate the influence of EFs on the EMT as well as the roles of PTEN and mTORC1 in this process. The effects of EFs on the EMT were investigated by analyzing the levels of specific proteins and transcription factors. The roles of mTORC1 and PTEN and their relationship with each other were studied via pharmacological inhibition or genetic knockdown. A Zeiss imaging system and scratch assays were used to study single-cell motility and monolayer cell migration. EFs induced a range of both biochemical changes (e.g., increased Snail, Slug, vimentin, and N-cadherin expression, decreased E-cadherin expression) and functional changes (e.g., enhanced migratory capacity) that are characteristic of the EMT. EF-stimulated cells exhibited suppressed PTEN expression, and further PTEN downregulation led to the acquisition of more mesenchymal features and the loss of epithelial characteristics, which was accompanied by increased migratory capacity. PTEN overexpression reversed the EF-induced EMT and inhibited the migratory capacity of keratinocytes. EF-induced mTORC1 activation was a required component of the causal relationship between PTEN

  20. Field-induced transition from chiral spin-triplet to mixed-parity Fulde-Ferrell-Larkin-Ovchinnikov superconductivity

    Science.gov (United States)

    Romano, Alfonso; Cuoco, Mario; Noce, Canio; Gentile, Paola; Annunziata, Gaetano

    2010-02-01

    We analyze the response to a magnetic field of a two-dimensional spin-triplet superconductor with chiral order parameter when triplet pairing is closely competing with the singlet one. The study is performed via numerical solution of the Bogoliubov-de Gennes equations, assuming that the translational symmetry is broken in one direction by the presence of an interface beyond which superconducting pairing is not effective. We show that as the intensity of the magnetic field is increased above a threshold value, the system undergoes a transition to a spatially inhomogeneous state of the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) type where chirality disappears and a singlet-triplet mixing takes place along the direction perpendicular to the interface. Subdominant singlet components are found to accompany the triplet dominant ones in both phases. They develop close to the interface at low fields, then turning continuously into oscillating long-range ones as the field is increased. A similar behavior is found for the magnetization. It nucleates at the interface in the chiral phase, then acquiring in the FFLO phase an oscillatory behavior reaching its maximum amplitude at the sites where the dominant triplet component has a node. At these sites, the local spin-resolved density of states exhibits strong resonances, associated with the formation of Andreev bound states, which tend to broaden and decay in intensity as increasingly high magnetic fields are considered.

  1. Quantum critical scaling for field-induced quantum phase transition in a periodic Anderson-like model polymer chain

    Science.gov (United States)

    Ding, L. J.; Zhong, Y.

    2017-07-01

    The quantum phase transition and thermodynamics of a periodic Anderson-like polymer chain in a magnetic field are investigated by Green's function theory. The T-h phase diagram is explored, wherein a crossover temperature T∗ denoting the gapless phase crossover into quantum critical regimes, smoothly connects near the critical fields to the universal linear line T∗ ∼ (h - hc,s), and ends at hc,s, providing a new route to capture quantum critical point (QCP). The quantum critical scaling around QCPs is demonstrated by analyzing magnetization, specific heat and Grüneisen parameter Γh, which provide direct access to distill the power-law critical exponents (β, δ and α) obeying the critical scaling relation α + β(1 + δ) = 2, analogous to the quantum spin system. Furthermore, scaling hypothesis equations are proposed to check the scaling analysis, for which all the data collapse onto a single curve or two independent branches for the plot against an appropriate scaling variable, indicating the self-consistency and reliability of the obtained critical exponents.

  2. Mechanism and electric field induced modification of magnetic exchange stiffness in transition metal thin films on MgO(001)

    Science.gov (United States)

    Pradipto, Abdul-Muizz; Akiyama, Toru; Ito, Tomonori; Nakamura, Kohji

    2017-07-01

    Magnetic exchange stiffness in TM/MgO(001) [transition metal (TM) = Fe, Co, and Ni] is investigated by means of the first-principles full-potential linearized augmented plane wave method. We find that while the exchange stiffness constants are positive (ferromagnetic) in all considered systems, there are negative energy orbital contributions to the exchange stiffness preferring antiferromagnetic alignment. The different contributions can be explained simply in terms of bandwidth narrowing of the dx z band arising from an introduction of spin canting on neighboring TM atoms along the x direction. This scenario reflects well the stability of the d bands, especially in the cases of Fe/MgO and Co/MgO, on going from the ferromagnetic state towards the spin spiral states, and the exchange stiffness constant may be determined by the position of the Fermi level. As for the Ni/MgO system, we find that the exchange stiffness constant is much smaller than in the other two cases due to the almost full occupation of the relevant d orbitals. When this mechanism which is associated with the bandwidth narrowing is applied to investigate the effect of external field on the exchange stiffness, we find that in both Fe/MgO and Co/MgO, the application of positive field increases the exchange stiffness due to the modification of the TM-O atomic distance.

  3. Three order increase in scanning speed of space charge-controlled KTN deflector by eliminating electric field induced phase transition in nanodisordered KTN

    Science.gov (United States)

    Zhu, Wenbin; Chao, Ju-Hung; Chen, Chang-Jiang; Yin, Shizhuo; Hoffman, Robert C.

    2016-01-01

    In this paper, we report a three orders-of-magnitude increase in the speed of a space-charge-controlled KTN beam deflector achieved by eliminating the electric field-induced phase transition (EFIPT) in a nanodisordered KTN crystal. Previously, to maximize the electro-optic effect, a KTN beam deflector was operated at a temperature slightly above the Curie temperature. The electric field could cause the KTN to undergo a phase transition from the paraelectric phase to the ferroelectric phase at this temperature, which causes the deflector to operate in the linear electro-optic regime. Since the deflection angle of the deflector is proportional to the space charge distribution but not the magnitude of the applied electric field, the scanning speed of the beam deflector is limited by the electron mobility within the KTN crystal. To overcome this speed limitation caused by the EFIPT, we propose to operate the deflector at a temperature above the critical end point. This results in a significant increase in the scanning speed from the microsecond to nanosecond regime, which represents a major technological advance in the field of fast speed beam scanners. This can be highly beneficial for many applications including high-speed imaging, broadband optical communications, and ultrafast laser display and printing. PMID:27610923

  4. Three order increase in scanning speed of space charge-controlled KTN deflector by eliminating electric field induced phase transition in nanodisordered KTN

    Science.gov (United States)

    Zhu, Wenbin; Chao, Ju-Hung; Chen, Chang-Jiang; Yin, Shizhuo; Hoffman, Robert C.

    2016-09-01

    In this paper, we report a three orders-of-magnitude increase in the speed of a space-charge-controlled KTN beam deflector achieved by eliminating the electric field-induced phase transition (EFIPT) in a nanodisordered KTN crystal. Previously, to maximize the electro-optic effect, a KTN beam deflector was operated at a temperature slightly above the Curie temperature. The electric field could cause the KTN to undergo a phase transition from the paraelectric phase to the ferroelectric phase at this temperature, which causes the deflector to operate in the linear electro-optic regime. Since the deflection angle of the deflector is proportional to the space charge distribution but not the magnitude of the applied electric field, the scanning speed of the beam deflector is limited by the electron mobility within the KTN crystal. To overcome this speed limitation caused by the EFIPT, we propose to operate the deflector at a temperature above the critical end point. This results in a significant increase in the scanning speed from the microsecond to nanosecond regime, which represents a major technological advance in the field of fast speed beam scanners. This can be highly beneficial for many applications including high-speed imaging, broadband optical communications, and ultrafast laser display and printing.

  5. Optical transmission theory for metal-insulator-metal periodic nanostructures

    Science.gov (United States)

    Blanchard-Dionne, Andre-Pierre; Meunier, Michel

    2017-01-01

    A semi-analytical formalism for the optical properties of a metal-insulator-metal periodic nanostructure using coupled-mode theory is presented. This structure consists in a dielectric layer in between two metallic layers with periodic one-dimensional nanoslit corrugation. The model is developed using multiple-scattering formalism, which defines transmission and reflection coefficients for each of the interface as a semi-infinite medium. Total transmission is then calculated using a summation of the multiple paths of light inside the structure. This method allows finding an exact solution for the transmission problem in every dimension regime, as long as a sufficient number of diffraction orders and guided modes are considered for the structure. The resonant modes of the structure are found to be related to the metallic slab only and to a combination of both the metallic slab and dielectric layer. This model also allows describing the resonant behavior of the system in the limit of a small dielectric layer, for which discontinuities in the dispersion curves are found. These discontinuities result from the out-of-phase interference of the different diffraction orders of the system, which account for field interaction for both inner interfaces of the structure.

  6. Gate-tunable Phase Transitions in 1T-TaS$_2$

    OpenAIRE

    Yu, Yijun; Yang, Fangyuan; Lu, Xiu Fang; Yan, Ya Jun; Cho, Y.H.; Ma, Liguo; Niu, Xiaohai; Kim, Sejoong; Son, Young-Woo; Feng, Donglai; Li, Shiyan; Cheong, Sang-Wook; Chen, Xian Hui; Zhang, Yuanbo

    2014-01-01

    The ability to tune material properties using gate electric field is at the heart of modern electronic technology. It is also a driving force behind recent advances in two-dimensional systems, such as gate-electric-field induced superconductivity and metal-insulator transition. Here we describe an ionic field-effect transistor (termed "iFET"), which uses gate-controlled lithium ion intercalation to modulate the material property of layered atomic crystal 1T-TaS$_2$. The extreme charge doping ...

  7. Direct observation of nanoscale Peltier and Joule effects at metal-insulator domain walls in vanadium dioxide nanobeams.

    Science.gov (United States)

    Favaloro, Tela; Suh, Joonki; Vermeersch, Bjorn; Liu, Kai; Gu, Yijia; Chen, Long-Qing; Wang, Kevin X; Wu, Junqiao; Shakouri, Ali

    2014-05-14

    The metal to insulator transition (MIT) of strongly correlated materials is subject to strong lattice coupling, which brings about the unique one-dimensional alignment of metal-insulator (M-I) domains along nanowires or nanobeams. Many studies have investigated the effects of stress on the MIT and hence the phase boundary, but few have directly examined the temperature profile across the metal-insulating interface. Here, we use thermoreflectance microscopy to create two-dimensional temperature maps of single-crystalline VO2 nanobeams under external bias in the phase coexisting regime. We directly observe highly localized alternating Peltier heating and cooling as well as Joule heating concentrated at the M-I domain boundaries, indicating the significance of the domain walls and band offsets. Utilizing the thermoreflectance technique, we are able to elucidate strain accumulation along the nanobeam and distinguish between two insulating phases of VO2 through detection of the opposite polarity of their respective thermoreflectance coefficients. Microelasticity theory was employed to predict favorable domain wall configurations, confirming the monoclinic phase identification.

  8. Electric field-induced phase transitions and composition-driven nanodomains in rhombohedral-tetragonal potassium-sodium niobate-based ceramics

    KAUST Repository

    Lv, Xiang

    2017-08-07

    The mechanisms behind the high piezoelectricity of (K,Na)NbO3-based lead-free ceramics were investigated, including electric field-induced phase transitions and composition-driven nanodomains. The construction of a rhombohedral-tetragonal (R-T) phase boundary, confirmed using several advanced techniques, allowed a large piezoelectric constant (d33) of 450 ± 5 pC/N to be obtained in (1-x)K0.4Na0.6Nb0.945Sb0.055O3-xBi0.5Na0.5(Hf1-ySny)O3 (0 ≤ x ≤ 0.06 and 0 ≤ y ≤ 0.5) ceramics possessing an ultralow ΔUT-R of 7.4 meV. More importantly, the existence of an intermediate phase, i.e., the electric-induced phase (EIP), bridging the rhombohedral R [Ps//(111)] and tetragonal T [Ps//(001)] phases during the polarization rotation was demonstrated. Striped nanodomains (∼40 nm) that easily responded to external stimulation were also observed in the ceramics with an R-T phase. Thus, the enhanced piezoelectric properties originated from EIP and the striped nanodomains.

  9. Deep-level spectroscopy in metal-insulator-semiconductor structures

    Science.gov (United States)

    Kurtz, A.; Muñoz, E.; Chauveau, J. M.; Hierro, A.

    2017-02-01

    In this study we present a method for measuring bulk traps using deep-level spectroscopy techniques in metal-insulator-semiconductor (MIS) structures. We will focus on deep-level transient spectroscopy (DLTS), although this can be extended to deep-level optical spectroscopy (DLOS) and similar techniques. These methods require the modulation of a depletion region either from a Schottky junction or from a highly asymmetric p-n junction, junctions that may not be realizable in many current material systems. This is the case of wide-bandgap semiconductor families that present a doping asymmetry or have a high residual carrier concentration or surface carrier accumulation, such as InGaN or ZnO. By adding a thin insulating layer and forming an MIS structure this problem can be circumvented and DLTS/DLOS can be performed under certain conditions. A model for the measurement of bulk traps in MIS structures is thus presented, focusing on the similarities with standard DLTS, maintaining when possible links to existing knowledge on DLTS and related techniques. The model will be presented from an equivalent circuit point of view. The effect of the insulating layer on DLTS is evaluated by a combination of simulations and experiments, developing methods for the measurement of these type of devices. As a validation, highly doped ZnO:Ga MIS devices have been successfully characterized and compared with a reference undoped sample using the methods described in this work, obtaining the same intrinsic levels previously reported in the literature but in material doped as high as 1× {{10}18} cm-3.

  10. Time and frequency-dependence of the electric field-induced phase transition in BaTiO3-BiZn1/2Ti1/2O3

    Science.gov (United States)

    Iamsasri, Thanakorn; Esteves, Giovanni; Choe, Hyeokmin; Vogt, Marco; Prasertpalichat, Sasiporn; Cann, David P.; Gorfman, Semën; Jones, Jacob L.

    2017-08-01

    The time and frequency dependence of the electric field-induced phase transition in BaTiO3-BiZn1/2Ti1/2O3 was studied using in situ X-ray diffraction. The kinetics of the field-induced phase transition between cubic and tetragonal phases was described using a modified Kolmogorov-Avrami-Ishibashi (KAI) equation. Unlike previous works, for which some assumptions (e.g., unimodal and Gaussian) on the distribution of transition rates are needed, the present work utilized Bayesian inference and a Markov chain Monte Carlo algorithm to obtain the distribution of transition rates empirically without a priori assumption on the distribution. The results show that the transition rate coefficient increases as the frequency of applied field increases. The mean value of exponent n in the modified-KAI equation was close to 1, implying that the field-induced phase transition is site saturated and the growth of the induced phase occurred primarily from the surface.

  11. Terahertz field induced electromigration

    DEFF Research Database (Denmark)

    Strikwerda, Andrew; Zalkovskij, Maksim; Iwaszczuk, Krzysztof;

    We report the first observation of THz-field-induced electromigration in sub-wavelength metallic gap structures after exposure to intense single-cycle, sub-picosecond electric field transients of amplitude up to 400 kV/cm.......We report the first observation of THz-field-induced electromigration in sub-wavelength metallic gap structures after exposure to intense single-cycle, sub-picosecond electric field transients of amplitude up to 400 kV/cm....

  12. Light Emission Characteristics of Metal/Insulator/Metal and Metal/Insulator/Si Tunnel Junctions Mediated by Surface Plasmon-polaritons

    Institute of Scientific and Technical Information of China (English)

    WANG Mao-xiang; YU Jian-hua; ZHANG You-wen; SUN Cheng-xiu; ZHANG Xu-ping

    2007-01-01

    The Au/Al2O3/Al metal/insulator/metal junction(MIMJ) and Au/SiO2/Si metal/insulator/Si junction(MISJ) have been constructed successfully. The light emission of these junctions was mediated by surface plasmon-polaritons(SPPs) under surface roughness. The light emission from MISJ was more uniform and stable than that from MIMJ. The light power of MISJ was about 2~3 orders higher than that of MIMJ. The light emission spectrum of MISJ was analyzed especially. In the spectrum, there was one main peak located at the wavelength of 610 nm~640 nm, which was mainly due to the couple of SPP with the surface roughness at the Au/air and Au/SiO2 interfaces. A weak peak located at the shorter wavelength region in the spectrum was also found, which was caused by the direct radiation of doped-Si plasma oscillation.

  13. Toward Super-Resolution Imaging at Green Wavelengths Employing Stratified Metal-Insulator Metamaterials

    Directory of Open Access Journals (Sweden)

    Masanobu Iwanaga

    2015-05-01

    Full Text Available Metamaterials (MMs are subwavelength-structured materials that have been rapidly developed in this century and have various potentials to realize novel phenomena, such as negative refraction, cloaking and super-resolution. Theoretical proposals for super-resolution image transfer using metallic thin films were experimentally demonstrated at ultraviolet and violet wavelengths from 365 to 405 nm. However, the most preferred wavelengths of optical imaging are green wavelengths around 500 nm, because optical microscopy is most extensively exploited in the area of biotechnology. In order to make the super-resolution techniques using MMs more practical, we propose the design of a stratified metal-insulator MM that has super-resolution image transfer modes at green wavelengths, which we here call hyper modes. The design assumed only Ag and SiO2 as constituent materials and was found employing Bloch-state analysis, which is based on a rigorous transfer-matrix method for the metal-insulator MMs. It is numerically substantiated that the designed stratified metal-insulator metamaterial (SMIM is capable of forming super-resolution images at the green wavelengths, and optical loss reduction is also studied. We discuss the results derived by the Bloch-state analysis and by effective medium models usually used for the metal-insulator MMs and show that the Bloch-state analysis is more suitable to reproduce the experimental data.

  14. Peltier effect in normal metal-insulator-heavy fermion metal junctions

    Science.gov (United States)

    Goltsev, A. V.; Rowe, D. M.; Kuznetsov, V. L.; Kuznetsova, L. A.; Min, Gao

    2003-04-01

    A theoretical study has been undertaken of the Peltier effect in normal metal-insulator-heavy fermion metal junctions. The results indicate that, at temperatures below the Kondo temperature, such junctions can be used as electronic microrefrigerators to cool the normal metal electrode and are several times more efficient in cooling than the normal metal-heavy fermion metal junctions.

  15. Model of coherent transport in metal-insulator-midband gap semiconductor-insulator-semiconductor structure

    Science.gov (United States)

    Abramov, I. I.; Danilyuk, A. L.

    1997-08-01

    A kinetic model of coherent transport with self-organized carrier transfer via midband gap semiconductor states in metal-insulator-midband gap semiconductor-insulator-semiconductor structure at room temperature is proposed. The coherent transport at room temperature can be a result of continuous oscillations of charge carriers at midband gap semiconductor states.

  16. High-channel-count plasmonic filter with the metal-insulator-metal Fibonacci-sequence gratings.

    Science.gov (United States)

    Gong, Yongkang; Liu, Xueming; Wang, Leiran

    2010-02-01

    Fibonacci-sequence gratings based on metal-insulator-metal waveguides are proposed. The spectrum properties of this structure are numerically investigated by using the transfer matrix method. Numerical results demonstrate that the proposed structure can generate high-channel-count plasmonic stop bands and can find significant applications in highly integrated dense wavelength division multiplexing networks.

  17. Field-induced phase transition in Bi{sub 1/2}Na{sub 1/2}TiO{sub 3}-based lead-free piezoelectric ceramics

    Energy Technology Data Exchange (ETDEWEB)

    Hinterstein, Manuel [TU Darmstadt (Germany). Inst. for Materials Science; TU Dresden (Germany). Inst. for Materials Science; Knapp, Michael [CELLS, Barcelona (Spain); Hoelzel, Markus; Jo, Wook; Fuess, Hartmut [TU Darmstadt (Germany). Inst. for Materials Science; Cervellino, Antonio [Paul Scherrer Institute, Villigen (Switzerland). Swiss Light Source; Ehrenberg, Helmut [TU Dresden (Germany). Inst. for Materials Science

    2010-12-15

    The origin of the electric field-induced strain in the polycrystalline ceramic 0.92Bi{sub 1/2}Na{sub 1/2}TiO{sub 3}-0.06BaTiO{sub 3}-0.02K{sub 1/2}Na{sub 1/2}NbO{sub 3} was investigated using in situ high-resolution X-ray and neutron diffraction techniques. The initially existing tetragonal phase with pseudocubic lattice undergoes a reversible phase transition to a significantly distorted rhombohedral phase under electric field, accompanied by a change in the oxygen octahedral tilting from a{sup 0}a{sup 0}c{sup +} to a{sup -}a{sup -}a{sup -} and in the tilting angle. The polarization values for the tetragonal and rhombohedral phases were calculated based on the structural information from Rietveld refinements. The large recoverable electric field-induced strain is a consequence of a reversible electric field-induced phase transition from an almost nonpolar tetragonal phase to a ferroelectrically active rhombohedral phase. (orig.)

  18. Nanosize effects on the magnetic field induced transitions in La{sub 0.67−x}Eu{sub x}Ca{sub 0.33}MnO{sub 3} perovskite manganite

    Energy Technology Data Exchange (ETDEWEB)

    Raju, N.; Roja Sree, D.; Reddy, S. Shravan Kumar; Reddy, Ch. Gopal [Department of Physics, Osmania University, Hyderabad 500007 (India); Reddy, P. Yadagiri, E-mail: yadagirireddy@yahoo.com [Department of Physics, Osmania University, Hyderabad 500007 (India); Reddy, K. Rama [Department of Physics, Osmania University, Hyderabad 500007 (India); Reddy, V. Raghavendra [UGC-DAE Consortium for Scientific Research, University Campus, Khandwa Road, Indore 452001 (India); Reddy Turpu, Goverdhan [Department of Pure and Applied Physics, Guru Ghasidas Vishwavidyalaya, Bilaspur 495009 C.G. (India)

    2014-11-15

    The nanosize effects on magnetic field induced transitions in La{sub 0.67−x}Eu{sub x}Ca{sub 0.33}MnO{sub 3} (x=0.25 and 0.27) system are presented in this paper. The reduction in the particle size of the system shows drastic effects on the electrical transport properties leading to robustness of the charge ordering phenomenon. The metal–insulator transition found in bulk materials at low magnetic fields disappeared in nanoparticles of the same material and a high field induced metal–insulator transition emerged at lower temperatures. These results manifest a strong correlation between the chemical pressures induced by doping of various ions at A-site and nanosize related phenomenon. - Highlights: • Chemical pressure and nanosize effects on electrical transport studies of Eu doped LCMO system are reported. • Decrease in particle size resulted in drastic changes on electrical transport studies. • Metal–insulator transition found in bulk at low magnetic fields disappeared in nanoparticles.

  19. The control of magnetism near metal-to-insulator transitions of VO2 nano-belts

    CSIR Research Space (South Africa)

    Nkosi, SS

    2016-12-01

    Full Text Available changes near the metal-insulator phase transition of VO(sub2) produces magnetoelastic anisotropy. We observe intrinsic paramagnetic centres (PM-C) both at the near film surface and bulk/deep PM-C that are affected by the metal-insulator phase transition...

  20. Theoretical Analysis of the Characteristic Impedance in Metal-Insulator-Metal Plasmonic Transmission Lines

    CERN Document Server

    Nejati, Hamid

    2013-01-01

    We propose a closed form formulation for the impedance of the Metal-Insulator-Metal (MIM) plasmonic transmission lines by solving the Maxwell's equations. We provide approximations for thin and thick insulator layers sandwiched between metallic layers. In the case of very thin dielectric layer, the surface waves on both interfaces are strongly coupled resulting in an almost linear dependence of the impedance of the plasmonic transmission line on the thickness of the insulator layer. On the other hand, for very thick insulator layer, the impedance does not vary with the insulator layer thickness due to the weak-coupling/decoupling of the surface waves on each metal-insulator interface. We demonstrate the effectiveness of our proposed formulation using two test scenarios, namely, almost zero reflection in Tee-junction and reflection from line discontinuity in the design of Bragg reflectors, where we compare our formulation against previously published results.

  1. Flexible perovskite solar cells based on the metal-insulator-semiconductor structure.

    Science.gov (United States)

    Wei, Jing; Li, Heng; Zhao, Yicheng; Zhou, Wenke; Fu, Rui; Pan, Huiyue; Zhao, Qing

    2016-09-14

    The metal-insulator-semiconductor (MIS) structure is applied to perovskite solar cells, in which the traditional compact layer TiO2 is replaced by Al2O3 as the hole blocking material to realize an all-low-temperature process. Flexible devices based on this structure are also realized with excellent flexibility, which hold 85% of their initial efficiency after bending 100 times.

  2. Influence of graphene oxide on metal-insulator-semiconductor tunneling diodes

    OpenAIRE

    Lin, Chu-Hsuan; Yeh, Wei-Ting; Chan, Chun-Hui; Lin, Chun-Chieh

    2012-01-01

    In recent years, graphene studies have increased rapidly. Graphene oxide, which is an intermediate product to form graphene, is insulating, and it should be thermally reduced to be electrically conductive. We herein describe an attempt to make use of the insulating properties of graphene oxide. The graphene oxide layers are deposited onto Si substrates, and a metal-insulator-semiconductor tunneling structure is formed and its optoelectronic properties are studied. The accumulation dark curren...

  3. Slow light in metal-insulator-metal waveguide by negative Goos-Hänchen shift

    Science.gov (United States)

    Oh, Geum-Yoon; Chheang, Vuthy; Kim, Doo-Gun; Kim, Tae-Ryong; Jun, Li; Kim, Hong-Seung; Choi, Young-Wan

    2014-12-01

    We demonstrated group velocity delay using a metal-insulator-metal structure for slow light that would be very simple to fabricate. A negative Goos-Hänchen shift of the surface plasmon resonance can be caused by incident radiation while reflecting, resulting in a general group delay. Using this phenomenon, we induced a group delay of 70 fs using a very simple 20-μm-long waveguide.

  4. Anisotropic cascade of field-induced phase transitions in the frustrated spin-ladder system BiCu2PO6.

    Science.gov (United States)

    Kohama, Yoshimitsu; Wang, Shuang; Uchida, Atsuko; Prsa, Krunoslav; Zvyagin, Sergei; Skourski, Yuri; McDonald, Ross D; Balicas, Luis; Ronnow, Henrik M; Rüegg, Christian; Jaime, Marcelo

    2012-10-19

    BiCu(2)PO(6) is a frustrated two-leg spin-ladder compound with a spin gap that can be closed with a magnetic field of approximately 20 T. This quantum phase transition and its related phase diagram as a function of magnetic field and temperature (H, T) are investigated up to 60 T by means of specific heat, magnetocaloric effect, magnetization, and magnetostriction measurements. In contrast to other gapped quantum magnets, BiCu(2)PO(6) undergoes a series of unexpected first- and second-order phase transitions when an external magnetic field is applied along the crystallographic c axis. The application of a magnetic field along the b axis induces two second-order phase transitions. We propose that the anisotropy and complex phase diagram result from the interplay between strong geometrical frustration and spin-orbit interaction necessary for the description of this fascinating magnetic system.

  5. Realization of Primary Thermometer from Electrical Shot Noise in a Metal-Insulator-Metal Tunnel Junction

    Energy Technology Data Exchange (ETDEWEB)

    Park, J. H.; Rehman, M.; Choi, J. S.; Song, W.; Chong, Y. [Korea Research Institute of Standards and Science, Daejeon (Korea, Republic of); Khim, Z. G. [Dept. of Physics and Astronomy, Seoul National University, Seoul (Korea, Republic of); Ryu, S. W. [Dept. of Physics, Chonnam National University, Gwangju (Korea, Republic of)

    2010-04-15

    We measured electrical shot noise in a metal-insulator-metal tunnel junction, which was made by using electron-beam lithography and double-angle evaporation technique. Since the dependence of the shot noise on bias voltage and temperature is theoretically well known, we can determine the temperature of the junction by measuring the noise as the voltage across the junction is changed. A cryogenic low noise amplifier was used to amplify the noise signal in the frequency range of 600-800 MHz, which enabled fast measurement of noise signal and thus temperature. With further study, this method could be useful for primary thermometry in cryogenic temperatures.

  6. On the surface recombination current of metal-insulator semiconductor inversion layer solar cells

    DEFF Research Database (Denmark)

    Nielsen, Otto M.

    1981-01-01

    Current voltage characteristics have been obtained under dark and illuminated conditions for Al-SiO2-pSi metal-insulator semiconductor inversion layer solar cells. The cells were fabricated on ~ and ~ oriented substrates with resistivities in the range of 8–15 Omega cm. For ~ cells the open circuit...... voltages Voc were found to be lower than for ~ cells. The measured differences in Voc were higher than expected from the dark characteristics which is explained as a difference in the surface recombination current due to a higher interface state density Nss of ~ cells. Journal of Applied Physics...

  7. Double metal-insulator transitions and MR in La{sub 0.67}Ca{sub 0.33}Mn{sub 1-x}Ru{sub x}O{sub 3} (x{<=}0.10): a qualitative understanding in light of possible magnetic phase separation

    Energy Technology Data Exchange (ETDEWEB)

    Lakshmi, L.S. E-mail: slaxmi73@hotmail.com; Sridharan, V. E-mail: sridh61@hotmail.com; Natarajan, D.V.; Rawat, Rajeev; Chandra, Sharat; Sastry, V.S.; Radhakrishnan, T.S. E-mail: tsr_res@vsnl.net

    2004-08-01

    We report results of the magnetotransport measurements on La{sub 0.67}Ca{sub 0.33}Mn{sub 1-x}Ru{sub x}O{sub 3} (0{<=}x{<=}0.1) compounds in the light of proposed magnetic phase separation in our previous work wherein two metal to insulator transitions (MITs) were reported (J. Magn. Magn. Mater. 257 (2003) 195). With the application of magnetic field, a significant reduction in resistance and a shift in MITs to higher temperatures but with different rates are observed. The temperature dependent magnetoresistance (MR) exhibits two maxima, a pronounced one at higher temperature and a shallow one at low temperature, corresponding to the two MITs. The peak value of MR at high temperature MITs (H=5 T) does not change systematically with Ru concentration. The low temperature MR peak becomes perceptible for x{>=}0.03 and shows a nominal enhancement with Ru concentration. The double maxima, both exhibiting MR phenomena in the magnetotransport properties of Ru-doped manganites are analysed within the context of magnetic phase separation.

  8. Magnetism and metal insulator transition in FeSi and FeGe. Ab Initio investigations of the electronic structure; Magnetismus und Metall-Isolator-Uebergang in FeSi und FeGe. Ab-initio-Untersuchungen der elektronischen Struktur

    Energy Technology Data Exchange (ETDEWEB)

    Neef, Matthias

    2007-03-19

    Aim of this thesis was to reach by a systematic study of different ab initio procedures an improved description of the electronic properties of FeSi and FeGe. Central result is the itinerant description of FeSi as a semiconductor in the neighbourhood of a ferromagnetic instability. The regardment of the nonlocal exchange in the effective one-particle approximation leads to a metastable magnetic state scarcely above the magnetic ground state. The application of the hybrid functional leads to a 1st order metal-isolator transition for large lattice parameters: FeSi transforms at increasement of the lattice parameter from an unmagnetic isolator to a magnetic metal. A similar behavior is found in the isostructural compound FeGe. The two systems FeSi and FeGe were systematically and detailedly analyzed by means of ab initio procedures. Thereby the structural, electronic, and magnetic properties were studied with DFT and HF calculations. Both calculations with spin polarization and without spin polarization were performed.

  9. Field-induced transition of the magnetic ground state from A-type antiferromagnetic to ferromagnetic order in CsCo2Se2

    Science.gov (United States)

    von Rohr, Fabian; Krzton-Maziopa, Anna; Pomjakushin, Vladimir; Grundmann, Henrik; Guguchia, Zurab; Schnick, Wolfgang; Schilling, Andreas

    2016-07-01

    We report on the magnetic properties of CsCo2Se2 with ThCr2Si2 structure, which we have characterized through a series of magnetization and neutron diffraction measurements. We find that CsCo2Se2 undergoes a phase transition to an antiferromagnetically ordered state with a Néel temperature of {{T}\\text{N}}≈ 66 K. The nearest neighbour interactions are ferromagnetic as observed by the positive Curie-Weiss temperature of \\Theta≈ 51.0 K. We find that the magnetic structure of CsCo2Se2 consists of ferromagnetic sheets, which are stacked antiferromagnetically along the tetragonal c-axis, generally referred to as A-type antiferromagnetic order. The observed magnitude of the ordered magnetic moment at T  =  1.5 K is found to be only 0.20(1){μ\\text{Bohr}}  / Co. Already in comparably small magnetic fields of {μ0}H{{}\\text{MM}}(5~K)≈ 0.3 T, we observe a metamagnetic transition that can be attributed to spin-rearrangements of CsCo2Se2, with the moments fully ferromagnetically saturated in a magnetic field of {μ0}{{H}\\text{FM}}(5~K)≈ 6.4 T. We discuss the entire experimentally deduced magnetic phase diagram for CsCo2Se2 with respect to its unconventionally weak magnetic coupling. Our study characterizes CsCo2Se2, which is chemically and electronically posed closely to the A x Fe2-y Se2 superconductors, as a host of versatile magnetic interactions.

  10. Domain configuration changes under electric field-induced antiferroelectric-ferroelectric phase transitions in NaNbO{sub 3}-based ceramics

    Energy Technology Data Exchange (ETDEWEB)

    Guo, Hanzheng, E-mail: hug17@psu.edu; Randall, Clive A. [Materials Research Institute, The Pennsylvania State University, University Park, Pennsylvania 16802 (United States); Shimizu, Hiroyuki; Mizuno, Youichi [Taiyo Yuden Co., Ltd., Takasaki, Gunma 370-3347 (Japan)

    2015-08-07

    We recently developed a feasible crystal chemistry strategy to stabilize the antiferroelectricity in NaNbO{sub 3} through a chemical substitution to decrease the tolerance factor and increase the average electronegativity of the system [Shimizu et al., Dalton Trans. 44, 10763 (2015) and Guo et al., J. Appl. Phys. 117, 214103 (2015)]. Two novel lead-free antiferroelectric (AFE) solid solutions, (1-x)NaNbO{sub 3}-xCaZrO{sub 3} and (1-x)NaNbO{sub 3}-xSrZrO{sub 3}, have been found to exhibit the double polarization hysteresis typical of a reversible AFE ↔ ferroelectric (FE) phase transition. In this study, as demonstrated by (1-x)NaNbO{sub 3}-xCaZrO{sub 3} system, the influence of chemical modification and electrical poling on the AFE/FE phase stability was investigated, primarily focusing on the microstructural and crystallographic evolutions. Together with the macroscopic polarization hysteresis measurements, a well-demonstrated structure-property relationship was presented. It was found that the CaZrO{sub 3} substitution into NaNbO{sub 3} can effectively destabilize the FE Q phase and correspondingly lead to a spontaneous reverting to AFE P phase. In contrast to the reversible AFE ↔ FE phase transition, the domain morphology evolution exhibits irreversible nature with a growing process of the orientational domains after applying electric field. Moreover, a multiple-zone axes electron diffraction map of P and Q phases has been summarized and is believed to be an efficient diagram to determine the AFE/FE nature of the NaNbO{sub 3}-based systems.

  11. Field-induced magnetic phase transitions and correlated electronic states in the hexagonal RAgGE and RPtIn series

    Energy Technology Data Exchange (ETDEWEB)

    Morosan, Emilia [Iowa State Univ., Ames, IA (United States)

    2005-01-01

    The present work was initially motivated by the desire to continue the study of complex metamagnetism in relation to the crystal structure of various compounds; this study already included tetragonal compounds like HoNi2B2C (Canfield 1997b; Kalatsky 1998) and DyAgSb2 (Myers 1999), in which the rare earths occupy unique tetragonal positions. We intended to find hexagonal systems suited for such a study, with complex metamagnetic properties, and the search for extremely anisotropic hexagonal compounds turned into a rewarding exploration. We identified and grew most of the heavy rare earth members of two isostructural series, RAgGe and RPtIn, both belonging to the hexagonal Fe2P family of materials. In each of these series we found one compound, TmAgGe, and TbPtIn respectively, that was suitable for a simple study of angular dependent metamagnetism: they had three rare earth ions in the unit cell, positioned at a unique crystallographic site with orthorhombic point symmetry. The magnetization of both TmAgGe and TbPtIn was extremely anisotropic, with larger values for the in-plane orientation of the applied field than in the axial direction. Complex metamagnetic transitions existed for field within the ab-plane, and, similar to the case of the tetragonal compounds RNi2B2C and DyAgSb2, they depended on the field orientation within the basal plane. We were thus able to develop a two-dimensional model, the three co-planar Ising-like systems model, which described well the angular dependence of the metamagnetic transitions in the TmAgGe and TbPtIn hexagonal compounds. Having three magnetic moments in the hexagonal unit cell, in orthorhombic point symmetry positions, added to the complexity of the analysis compared to the case of tetragonal compounds having one rare earth atom per unit cell, in tetragonal point symmetry. However, the three co-planar Ising-like systems model yielded complex, but

  12. Fingerprints of field-induced Berezinskii-Kosterlitz-Thouless transition in quasi-two-dimensional S=1/2 Heisenberg magnets Cu(en)(H2O)2SO4 and Cu(tn)Cl2

    Science.gov (United States)

    Baranová, Lucia; Orendáčová, Alžbeta; Čižmár, Erik; Tarasenko, Róbert; Tkáč, Vladimír; Orendáč, Martin; Feher, Alexander

    2016-04-01

    Organo-metallic compounds Cu(en)(H2O)2SO4 (en=C2H8N2) and Cu(tn)Cl2 (tn=C3H10N2) representing S=1/2 quasi-two-dimensional Heisenberg antiferromagnets with an effective intra-layer exchange coupling J/kB≈3 K, have been examined by specific heat measurements at temperatures down to nominally 50 mK and magnetic fields up to 14 T. A comparative analysis of magnetic specific heat in zero magnetic field revealed nearly identical contribution of short-range magnetic correlations and significant differences were observed at lowest temperatures. A phase transition to long-range order was observed in Cu(en)(H2O)2SO4 at TC=0.9 K while hidden in Cu(tn)Cl2. A response of both compounds to the application of magnetic field has rather universal features characteristic for a field-induced Berezinskii-Kosterlitz-Thouless transition theoretically predicted for ideal two-dimensional magnets.

  13. Temperature-induced and electric-field-induced phase transitions in rhombohedral Pb(In 1 /2Nb1 /2) O3-Pb(Mg 1 /3Nb2 /3)O3-PbTiO3 ternary single crystals

    Science.gov (United States)

    Wang, Yaojin; Wang, Zhiguang; Ge, Wenwei; Luo, Chengtao; Li, Jiefang; Viehland, D.; Chen, Jianwei; Luo, Haosu

    2014-10-01

    Temperature and electric field effects on rhombohedral (R ) ternary Pb(In 1 /2Nb1 /2) O3-Pb(Mg 1 /3Nb2 /3)O3-PbTiO3 (PIN-PMN-PT) ferroelectric single crystals were comprehensively studied by x-ray diffraction. We have focused on how the individual phase transitions as well as the phase transition sequences depend on thermal and electrical history. Electric field-temperature phase diagrams have been constructed under [001] field-cooling and field-heating conditions. As happens to the R phase of binary PMN-PT crystals [H. Cao, J. F. Li, D. Viehland, and G. Y. Xu, Phys. Rev. B 73, 184110 (2006), 10.1103/PhysRevB.73.184110], the R phase of the zero-field-cooled (ZFC) state is replaced by a monoclinic A (M A) phase in the field-cooled (FC) diagram. In particular, reciprocal-space mesh scans demonstrated that the M A phase was stable for crystals poled along the [001] crystallographic direction rather than the initial R phase of the ZFC state. Furthermore, an E -field-induced phase transformational sequence of R →M A→ tetragonal (T ) was observed at constant temperature, revealing a gradual increase in the c lattice parameter. These findings demonstrate that the ternary PIN-PMN-PT crystals exhibit common phase transition features with binary PMN-PT and Pb(Zn 1 /3Nb2 /3)O3-PbTiO3 (PZN-PT) ones for compositions in the low PT side of the morphotropic phase boundary.

  14. Influence of Doping on the Mott Metal-Insulator Transition in Infinite Dimensions

    Institute of Scientific and Technical Information of China (English)

    TONG Ning-Hua

    2002-01-01

    We have studied the effect of hole-doping on the established scenerio of the first-order Mott metal-insulatortransition (MIT) at half-filling using dynamical mean-Seld theory and exact diagonalization technique. The Mott insu-lator state is changed into metallic state immediately as holes are doped into the system. The latter is expected to beFermi liquid. The previously found unanalytical structure of MIT no longer exists for doping as small as 2 percent. Wecompare our results with that obtained from Gutzwiller approximation.

  15. Mott-Hubbard and Anderson metal-insulator transitions in correlated lattice fermions with binary disorder

    OpenAIRE

    Semmler, Denis; Byczuk, Krzysztof; Hofstetter, Walter

    2009-01-01

    Strongly correlated fermions in a crystal or in an optical lattice in the presence of binary alloy disorder are investigated. We employ the statistical dynamical mean-field theory, which incorporates both, local fluctuations due to disorder and local correlations due to interaction, to solve the Anderson-Hubbard model. Localization due to disorder is studied by means of the probability distribution function of the local density of states. We obtain a complete paramagnetic ground state phase d...

  16. Mesoscopic Effects and Metal-Insulator Transition in Vanadium Oxide Nanowires

    Science.gov (United States)

    2012-07-08

    clean, pattern and dope VO2 nanobeams, rods and plates, and epitaxial VO2 films on TiO2. We studied the competition between 1. REPORT DATE (DD-MM-YYYY...We found several improved ways to grow, manipulate, clean, pattern and dope VO2 nanobeams, rods and plates, and epitaxial VO2 films on TiO2. We...to 4.0 (4.0 max scale): Number of graduating undergraduates funded by a DoD funded Center of Excellence grant for Education, Research and Engineering

  17. Phenomenological Model for the metal-insulator transition in two dimensions

    OpenAIRE

    Weisz, J. F.

    2009-01-01

    The resistivity measured in two-dimensional MOSFET geometry is modeled by considering that the resistivity is a function of the temperature and the areal density of charges (electrons or holes). The logistics differential equation is proposed for the behaviour of the resistivity as a function of temperature, so that the two phases are obtained in a natural manner. At low temperatures, the Drude model behaviour is assumed for the resistivity as a function of density. Two characteristics then f...

  18. Metal-Insulator Transition Associated with [0110] Charge Ordering in (EDO-TTF)_2X

    Science.gov (United States)

    Drozdova, O.; Tanner, D. B.; Yakushi, K.; Ota, A.; Yamochi, H.; Saito, G.

    2002-03-01

    Optical (polarized infrared-visible reflectance and Raman) spectra of (EDO-TTF)_2X (X= PF_6, T_MI= 280 K; AsF_6, T_MI= 268 K) have been measured at temperatures above and below T_MI. From the frequencies of three charge-sensitive C=C stretching modes of EDO-TTF, the molecular charge was estimated as uniform +0.5 split below T_MI to (0, +1). In the electronic spectra along the stack, the main conductivity peak vanishes and instead, two charge transfer bands CT1 (4500 cm-1) and CT2 (11150 cm-1) appear corresponding to D^0D^+...D^+D^0 and D^+D^+...D^2+D^0 processes, respectively. For the first time, the electron-molecular vibration (EMV) coupling between two C=C modes of D^+ and CT2 was observed in the polarized Raman spectra. The optical data point out the importance of the EMV coupling in the formation of the [0110] charge-ordering pattern.

  19. Absence of disorder-driven metal-insulator transitions in simple holographic models

    CERN Document Server

    Grozdanov, Sašo; Sachdev, Subir; Schalm, Koenraad

    2015-01-01

    We study electrical transport in a strongly coupled strange metal in two spatial dimensions at finite temperature and charge density, holographically dual to Einstein-Maxwell theory in an asymptotically $\\mathrm{AdS}_4$ spacetime, with arbitrary spatial inhomogeneity, up to mild assumptions. In condensed matter, these are candidate models for exotic strange metals without long-lived quasiparticles. We prove that the electrical conductivity is bounded from below by a universal minimal conductance: the quantum critical conductivity of a clean, charge-neutral plasma. Beyond non-perturbatively justifying mean-field approximations to disorder, our work demonstrates the practicality of new hydrodynamic insight into holographic transport.

  20. Absence of Disorder-Driven Metal-Insulator Transitions in Simple Holographic Models

    Science.gov (United States)

    Grozdanov, Sašo; Lucas, Andrew; Sachdev, Subir; Schalm, Koenraad

    2015-11-01

    We study electrical transport in a strongly coupled strange metal in two spatial dimensions at finite temperature and charge density, holographically dual to the Einstein-Maxwell theory in an asymptotically four-dimensional anti-de Sitter space spacetime, with arbitrary spatial inhomogeneity, up to mild assumptions including emergent isotropy. In condensed matter, these are candidate models for exotic strange metals without long-lived quasiparticles. We prove that the electrical conductivity is bounded from below by a universal minimal conductance: the quantum critical conductivity of a clean, charge-neutral plasma. Beyond nonperturbatively justifying mean-field approximations to disorder, our work demonstrates the practicality of new hydrodynamic insight into holographic transport.

  1. Nanoscale temperature sensor based on Fano resonance in metal-insulator-metal waveguide

    Science.gov (United States)

    Kong, Yan; Wei, Qi; Liu, Cheng; Wang, Shouyu

    2017-02-01

    In order to realize temperature measurements with high sensitivity using compact structure, a nanoscale metal-insulator-metal waveguide based sensor combining with Fano resonance is proposed in this paper. Sealed ethanol in resonant cavity is adopted to further improve sensing performance. Additionally, dual resonant cavity based configuration is designed to generate a Fano-based sharp and asymmetric spectrum, providing high figure of merit in measurements. Moreover, structural parameters are optimized considering both transmission rate and spectral peak width. Certified by numerical calculation, sensitivity of 0.36 nm/°C is acquired with the optimized structure, indicating the designed sensor can play an important role in the nano-integrated plasmonic devices for high-accurate temperature detection.

  2. Optical magnetism and plasmonic Fano resonances in metal-insulator-metal oligomers.

    Science.gov (United States)

    Verre, R; Yang, Z J; Shegai, T; Käll, M

    2015-03-11

    The possibility of achieving optical magnetism at visible frequencies using plasmonic nanostructures has recently been a subject of great interest. The concept is based on designing structures that support plasmon modes with electron oscillation patterns that imitate current loops, that is, magnetic dipoles. However, the magnetic resonances are typically spectrally narrow, thereby limiting their applicability in, for example, metamaterial designs. We show that a significantly broader magnetic response can be realized in plasmonic pentamers constructed from metal-insulator-metal (MIM) sandwich particles. Each MIM unit acts as a magnetic meta-atom and the optical magnetism is rendered quasi-broadband through hybridization of the in-plane modes. We demonstrate that scattering spectra of individual MIM pentamers exhibit multiple Fano resonances and a broad subradiant spectral window that signals the magnetic interaction and a hierarchy of coupling effects in these intricate three-dimensional nanoparticle oligomers.

  3. Functional metal-insulator-metal top contacts for Si-based color photodetectors

    Science.gov (United States)

    Butun, Serkan; Aydin, Koray

    2016-12-01

    Here, we report on Si-based color photodetectors using monolithically integrated metal-insulator-metal Fabry-Perot cavity top contacts. Contacts were formed by depositing Ag/SiO2/Ag layers with different oxide thicknesses for each color. This allowed controlling the transmission band position and width while maintaining the high conductivity. We have obtained over 55% external quantum efficiency for different colors both numerically and experimentally. The FWHM was less than 50 nm and the rejection ratio was an order of magnitude for each color. The total transmission through these top contacts exceeded that of dye filters used in conventional color CCDs and CMOS imaging arrays. In addition, these contacts performed similarly to recently proposed plasmonic hole array filters without the necessity of complicated fabrication steps like FIB milling and e-beam lithography. This type of top contacts can serve as a cheap alternative to dye filters used in contemporary devices without making the fabrication complicated.

  4. Flexible high-κ/Metal gate metal/insulator/metal capacitors on silicon (100) fabric

    KAUST Repository

    Rojas, Jhonathan Prieto

    2013-10-01

    Implementation of memory on bendable substrates is an important step toward a complete and fully developed notion of mechanically flexible computational systems. In this paper, we have demonstrated a simple fabrication flow to build metal-insulator-metal capacitors, key components of dynamic random access memory, on a mechanically flexible silicon (100) fabric. We rely on standard microfabrication processes to release a thin sheet of bendable silicon (area: 18 {\\ m cm}2 and thickness: 25 \\\\mu{\\ m m}) in an inexpensive and reliable way. On such platform, we fabricated and characterized the devices showing mechanical robustness (minimum bending radius of 10 mm at an applied strain of 83.33% and nominal strain of 0.125%) and consistent electrical behavior regardless of the applied mechanical stress. Furthermore, and for the first time, we performed a reliability study suggesting no significant difference in performance and showing an improvement in lifetime projections. © 1963-2012 IEEE.

  5. Phonon-Plasmon Interaction in Metal-Insulator-Metal Localized Surface Plasmon Systems

    CERN Document Server

    Mrabti, Abdelali; Nicolas, Rana; Maurer, Thomas; Adam, Pierre-Michel; Akjouj, Abdellatif; Pennec, Yan; Djafari-Rouhani, Bahram

    2016-01-01

    We investigate theoretically and numerically the coupling between elastic and localized surface plasmon modes in a system of gold nanocylinders separated from a thin gold film by a dielectric spacer of few nanometers thickness. That system supports plasmon modes confined in between the bottom of the nanocylinder and the top of the gold film, which arise from the formation of interference patterns by short-wavelength metal-insulator-metal propagating plasmon. First we present the plasmonic properties of the system though computer-simulated extinction spectra and field maps associated to the different optical modes. Next a simple analytical model is introduced, which allows to correctly reproduce the shape and wavelengths of the plasmon modes. This model is used to investigate the efficiency of the coupling between an elastic deformation and the plasmonic modes. In the last part of the paper, we present the full numerical simulations of the phononic properties of the system, and then compute the acousto-plasmon...

  6. Investigation on Photoelectric Behavior of Metal-Insulator-Semiconductor Structure Based on Titania Nanotubes Arrays

    Science.gov (United States)

    Wang, Lili; Panaitescu, Eugen; Richter, Christiaan; Menon, Latika

    2014-03-01

    Titanium dioxide (TiO2) has attracted great interest as an inexpensive, earth-abundant and environment-friendly anode material for next generation photovoltaic devices and the metal-insulator-semiconductor (MIS) concept is one of the most promising approaches for improving solar cell cost effectiveness (in /W). We investigated hybrid MIS structures of semiconducting ordered titania nanotube arrays integrated with insulating iron oxide or copper oxide layers and metallic copper. The morphological and structural properties of the samples were analyzed by scanning and transmission electron microscopy, energy-dispersive X-ray spectroscopy with elemental mapping, and X-ray diffraction. The nanotubular morphology represents a step change from the current thin film approach, providing significantly larger surface area while facilitating the charge separation and electron transport. Photoelectric behavior of the new structures was estimated by transient response, quantum efficiency and spectral response, and a solar simulator was used for recording the photovoltaic response.

  7. Hydrogen interaction with GaN metal-insulator-semiconductor diodes

    Energy Technology Data Exchange (ETDEWEB)

    Irokawa, Y., E-mail: IROKAWA.Yoshihiro@nims.go.jp [National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044 (Japan)

    2012-08-01

    Interaction mechanism of hydrogen with GaN metal-insulator-semiconductor (MIS) diodes is investigated, focusing on the metal/semiconductor interfaces. For MIS Pt-GaN diodes with a SiO{sub 2} dielectric, the current-voltage (I-V) characteristics reveal that hydrogen changes the conduction mechanisms from Fowler-Nordheim tunneling to Poole-Frenkel emission. In sharp contrast, Pt-Si{sub x}N{sub y}-GaN diodes exhibit Poole-Frenkel emission in nitrogen and do not show any change in the conduction mechanism upon exposure to hydrogen. The capacitance-voltage (C-V) study suggests that the work function change of the Schottky metal is not responsible mechanism for the hydrogen sensitivity.

  8. High-Resolution Plasmonic Refractive-Index Sensor Based on a Metal-Insulator-Metal Structure

    Institute of Scientific and Technical Information of China (English)

    ZHU Jia-Hu; HUANG Xu-Guang; MEI Xian

    2011-01-01

    @@ A high-resolution plasmonic refractive-index sensor based on a metal-insulator-metal structure consisting of a straight bus waveguide and a resonator waveguide is proposed and numerically simulated by using the finite difference time domain method under a perfectly matched layer absorbing boundary condition.Both analytic and simulated results show that the resonant wavelengths of the sensor have a linear relationship with the refractive index of material under sensing.Based on the relationship,the refractive index of the material can be obtained from the detection of one of the resonant wavelengths.The resolution of refractive index of the nanometeric plasmonic sensor can reach as high as 10-6,giving the wavelength resolution of 0.01 nm.It could be applied to highly-resolution biological sensing.%A high-resolution plasmonic refractive-index sensor based on a metal-insulator-metal structure consisting of a straight bus waveguide and a resonator waveguide is proposed and numerically simulated by using the finite difference time domain method under a perfectly matcted layer absorbing boundary conditition. Both analytic and simulated results show that the resonant wavelengths of the sensor have a linear relationship with the refractive index of material under sensing. Based on the relationship, the refractive index of the material can be obtained from the detection of one of the resonant wavelengths. The resolutio of refractive index of the nanometeric plasmonic sensor can reach as high as 1O-6, giving the wavelength resolution of 0.01 nm. It could be applied to highly- resolution biological sensing.

  9. Electric-field Induced Microdynamics of Charged Rods

    Directory of Open Access Journals (Sweden)

    Kyongok eKang

    2014-12-01

    Full Text Available Electric-field induced phase/state transitions are observed in AC electric fields with small amplitudes and low frequencies in suspensions of charged fibrous viruses (fd, which are model systems for highly charged rod-like colloids. Texture- and particle-dynamics in these field-induced states, and on crossing transition lines, are explored by image time-correlation and dynamic light scattering, respectively. At relatively low frequencies, starting from a system within the isotropic-nematic coexistence region, a transition from a nematic to a chiral nematic is observed, as well as a dynamical state where nematic domains melt and reform. These transitions are preliminary due to field-induced dissociation/association of condensed ions. At higher frequencies a uniform state is formed that is stabilized by hydrodynamic interactions through field-induced electro-osmotic flow where the rods align along the field direction. There is a point in the field-amplitude versus frequency plane where various transition lines meet. This point can be identified as a non-equilibrium critical point, in the sense that a length scale and a time scale diverge on approach of that point. The microscopic dynamics exhibits discontinuities on crossing transition lines that were identified independently by means of image and signal correlation spectroscopy.

  10. A transparent electrochromic metal-insulator switching device with three-terminal transistor geometry

    Science.gov (United States)

    Katase, Takayoshi; Onozato, Takaki; Hirono, Misako; Mizuno, Taku; Ohta, Hiromichi

    2016-05-01

    Proton and hydroxyl ion play an essential role for tuning functionality of oxides because their electronic state can be controlled by modifying oxygen off-stoichiometry and/or protonation. Tungsten trioxide (WO3), a well-known electrochromic (EC) material for smart window, is a wide bandgap insulator, whereas it becomes a metallic conductor HxWO3 by protonation. Although one can utilize electrochromism together with metal-insulator (MI) switching for one device, such EC-MI switching cannot be utilized in current EC devices because of their two-terminal structure with parallel-plate configuration. Here we demonstrate a transparent EC-MI switchable device with three-terminal TFT-type structure using amorphous (a-) WO3 channel layer, which was fabricated on glass substrate at room temperature. We used water-infiltrated nano-porous glass, CAN (calcium aluminate with nano-pores), as a liquid-leakage-free solid gate insulator. At virgin state, the device was fully transparent in the visible-light region. For positive gate voltage, the active channel became dark blue, and electrical resistivity of the a-WO3 layer drastically decreased with protonation. For negative gate voltage, deprotonation occurred and the active channel returned to transparent insulator. Good cycleability of the present transparent EC-MI switching device would have potential for the development of advanced smart windows.

  11. High voltage trapping effects in GaN-based metal-insulator-semiconductor transistors

    Science.gov (United States)

    Meneghesso, Gaudenzio; Meneghini, Matteo; Silvestri, Riccardo; Vanmeerbeek, Piet; Moens, Peter; Zanoni, Enrico

    2016-01-01

    This paper presents an analysis of the high voltage trapping processes that take place in high-electron mobility transistors based on GaN, with a metal-insulator-semiconductor (MIS) structure. The study is based on combined pulsed and transient measurements, carried out with trapping voltages in the range from 50 to 500 V. The results indicate that: (i) dynamic Ron is maximum for trapping voltages between 200 and 300 V, and decreases for higher voltage levels; (ii) Ron-transient measurements reveal the presence of a dominant trap with activation energy Ea1 = 0.93 eV and of a second trap with activation energy equal to Ea2 = 0.61 eV; (iii) the deep level transient spectroscopy (DLTS) signal associated to trap Ea1 is completely suppressed for high trapping voltages (VDS = 500 V). The results are interpreted by considering that the trap Ea1 is located in the buffer, and originates from CN defects. The exposure to high drain voltages may favor the depletion of such traps, due to a field-assisted de-trapping process or to the presence of vertical leakage paths.

  12. Stress-induced self-rolled metal/insulator bifilm microtube with micromesh walls

    Science.gov (United States)

    Lee, Kook-Nyung; Seo, Yeong-Tai; Lee, Min-Ho; Jung, Suk-Won; Kim, Yong-Kweon; Kim, Jung-Mu; Kyeong Seong, Woo

    2013-01-01

    A metal/insulator microtube with micromesh walls was constructed using stress-assisted self-rolling technology. The mesh-sidewall Pt/Ti/SiO2 microtube was self-formed by a tensile-stressed metal Pt/Ti film deposited onto a pre-patterned SiO2 micromesh layer. The microtube measured about 25 µm in diameter and was longer than 7 mm. The sidewall of the microtube was a square mesh, 5-20 µm long, and was electrically connected to electrical pads for electrical conductance measurement. The electrical resistance of the rolled-up microtube was measured to be 250-350 Ω when the microtube resistor's length was around 540 µm. The real-time measurement of the conductance change of the microtube with a Pt resistor could monitor the temperature change generated by heat injection. The microtube with micromesh walls is expected to be an interesting structure that has promising potential for use in electronics, chemical and biological applications.

  13. Reflective plasmonic waveplates based on metal-insulator-metal subwavelength rectangular annular arrays

    Science.gov (United States)

    Chen, Zhonghui; Wang, Chinhua; Xu, Fuyang; Lou, Yimin; Cao, Bing; Li, Xiaofeng

    2014-04-01

    We propose and present a quarter-wave plate using metal-insulator-metal (MIM) structure with sub-wavelength rectangular annular arrays (RAA) patterned in the upper Au film. It is found that by manipulating asymmetric width of the annular gaps along two orthogonal directions, the reflected amplitude and phase of the two orthogonal components can be well controlled via the RAA metasurface tuned by the MIM cavity effect, in which the localized surface plasmon resonance dip can be flattened with the cavity length. A quarter-wave plate has been realized through an optimized design at 1.55 μm, in which the phase difference variation of less than 2% of the π/2 between the two orthogonal components can be obtained in an ultra-wide wavelength range of about 130 nm, and the reflectivity is up to ˜90% within the whole working wavelength band. It provides a great potential for applications in advanced nanophotonic devices and integrated photonic systems.

  14. Electro-optic metal-insulator-semiconductor-insulator-metal Mach-Zehnder plasmonic modulator

    Science.gov (United States)

    Thomas, Roney; Ikonic, Zoran; Kelsall, Robert W.

    2012-01-01

    The performance of a CMOS-compatible electro-optic Mach-Zehnder plasmonic modulator is investigated using electromagnetic and carrier transport simulations. Each arm of the Mach-Zehnder device comprises a metal-insulator-semiconductor-insulator-metal (MISIM) structure on a buried oxide substrate. Quantum mechanical effects at the oxide/semiconductor interfaces were considered in the calculation of electron density profiles across the structure, in order to determine the refractive index distribution and its dependence on applied bias. This information was used in finite element simulations of the electromagnetic modes within the MISIM structure in order to determine the Mach-Zehnder arm lengths required to achieve destructive interference and the corresponding propagation loss incurred by the device. Both inversion and accumulation mode devices were investigated, and the layer thicknesses and height were adjusted to optimise the device performance. A device loss of <8 dB is predicted for a MISIM structure with a 25 nm thick silicon layer, for which the device length is <3 μm, and <5 dB loss is predicted for the limiting case of a 5 nm thick silicon layer in a 1.2 μm long device: in both cases, the maximum operating voltage is 7.5 V.

  15. Negative capacitance in optically sensitive metal-insulator-semiconductor-metal structures

    Science.gov (United States)

    Mikhelashvili, V.; Padmanabhan, R.; Meyler, B.; Yofis, S.; Eisenstein, G.

    2016-12-01

    We report a strong negative capacitance effect in back to back combination of a metal-insulator-semiconductor (MIS) structure and a metal-semiconductor junction, which is fabricated on an n type Silicon-on-Insulator substrate. The MIS capacitor comprises a SiO2-HfO2 insulator stack with embedded Pt nanoparticles. The capacitor undergoes a voltage stress process and thereby turns into a varactor and a photodetector. The negative capacitance is observed only under illumination in structures that employ a Schottky back contact. A symmetric double or an asymmetric single negative capacitance peak is observed depending on the nature of illumination. The phenomenon is attributed to the modulation of the semiconductor conductance due to photo generated carriers and their incorporation in trapping/de-trapping processes on interfacial and post filamentation induced defects in the insulator stack. The frequency range of the observed effect is limited to 100 kHz. Large ratios of light to dark and maximum to minimum of negative capacitances as well as of the obtained sensitivity to the applied voltage are, respectively, 105, more than 100, and 10-15. These were measured at 10 kHz under illumination at 365 nm with a power of 2.5 × 10-6 W.

  16. Transport properties of metal-metal and metal-insulator heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Fadlallah Elabd, Mohamed Mostafa

    2010-06-09

    In this study we present results of electronic structure and transport calculations for metallic and metal-insulator interfaces, based on density functional theory and the non-equilibrium Green's function method. Starting from the electronic structure of bulk Al, Cu, Ag, and Au interfaces, we study the effects of different kinds of interface roughness on the transmission coefficient (T(E)) and the I-V characteristic. In particular, we compare prototypical interface distortions, including vacancies, metallic impurities, non-metallic impurities, interlayer, and interface alloy. We find that vacancy sites have a huge effect on transmission coefficient. The transmission coefficient of non-metallic impurity systems has the same behaviour as the transmission coefficient of vacancy system, since these systems do not contribute to the electronic states at the Fermi energy. We have also studied the transport properties of Au-MgO-Au tunnel junctions. In particular, we have investigated the influence of the thickness of the MgO interlayer, the interface termination, the interface spacing, and O vacancies. Additional interface states appear in the O-terminated configuration due to the formation of Au-O bonds. An increasing interface spacing suppresses the Au-O bonding. Enhancement of T(E) depends on the position and density of the vacancies (the number of vacancies per unit cell). (orig.)

  17. Systematic study of metal-insulator-metal diodes with a native oxide

    KAUST Repository

    Donchev, E.

    2014-10-07

    © 2014 SPIE. In this paper, a systematic analysis of native oxides within a Metal-Insulator-Metal (MIM) diode is carried out, with the goal of determining their practicality for incorporation into a nanoscale Rectenna (Rectifying Antenna). The requirement of having a sub-10nm oxide scale is met by using the native oxide, which forms on most metals exposed to an oxygen containing environment. This, therefore, provides a simplified MIM fabrication process as the complex, controlled oxide deposition step is omitted. We shall present the results of an investigation into the current-voltage characteristics of various MIM combinations that incorporate a native oxide, in order to establish whether the native oxide is of sufficient quality for good diode operation. The thin native oxide layers are formed by room temperature oxidation of the first metal layer, deposited by magnetron sputtering. This is done in-situ, within the deposition chamber before depositing the second metal electrode. Using these structures, we study the established trend where the bigger the difference in metal workfunctions, the better the rectification properties of MIM structures, and hence the selection of the second metal is key to controlling the device\\'s rectifying properties. We show how leakage current paths through the non-optimised native oxide control the net current-voltage response of the MIM devices. Furthermore, we will present the so-called diode figures of merit (asymmetry, non-linearity and responsivity) for each of the best performing structures.

  18. Applications of Cubic MgZnO Thin Films in Metal-Insulator-Silicon Structures

    Institute of Scientific and Technical Information of China (English)

    LIANG Jun; WU Hui-Zhen; LAO Yan-Feng; QIU Dong-Jiang; CHEN Nai-Bo; XU Tian-Ning

    2004-01-01

    @@ Cubic Mgo.55Zno.45O thin film alloys have been deposited on Si substrates at low growth temperature. The topography of the cross section of the epitaxial film by scanning electronic microscope demonstrates good mor phology and high interfacial quality. The high (001) orientation and wide band-gap (Eg > 5.5 eV) of the cubic Mgo.55Zno.45 O thin films accord with the guidelines for metal-insulator-silicon (MIS) device applications. Using the cubic ternary thin films as insulators, MIS structures have been fabricated. The capacitance-voltage measurements show the flat band voltage shift VFB of11.8 V and mobile ion density Dmc of 5.57 × 1010 cm-2 for the MIS structure. Leakage current density as low as ~ 10-7 A/cm2 is obtained at E = 700 kV/cm by the currentvoltage measurements. These unique structural and electrical properties of the fabricated MIS devices indicate that cubic MgZnO materials could become a new candidate for high-κ dielectrics used in silicon integrated circuit technologies.

  19. Angular dependence of optical modes in metal-insulator-metal coupled quantum well infrared photodetector

    Energy Technology Data Exchange (ETDEWEB)

    Jing, YouLiang; Li, ZhiFeng, E-mail: zfli@mail.sitp.ac.cn; Chen, PingPing; Zhou, XiaoHao; Wang, Han; Li, Ning; Lu, Wei, E-mail: luwei@mail.sitp.ac.cn [National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, 500 Yutian Road, Shanghai 200083 (China); Li, Qian [Microsystem & Terahertz Research Center, China Academy of Engineering Physics, No 596, Yinhe Road, Chengdu 610200, Sichuan Province (China)

    2016-04-15

    We report the dependence of the near-field optical modes in metal-insulator-metal quantum well infrared photodetector (MIM-QWIP) on the incident angles. Three optical modes are observed and attributed to the 2nd- and the 3rd-order surface plasmon polariton (SPP) modes and the localized surface polariton (LSP) mode. In addition to the observation of a responsivity enhancement of 14 times by the LSP mode, the varying pattern of the three modes against the incident angle are revealed, in which the LSP mode is fixed while the 2nd SPP mode splits into two branches and the 3rd SPP mode red-shifts. The detailed mechanisms are analyzed and numerically simulated. The results fit the experiments very well, demonstrating the wavevector coupling effect between the incident light and the metal gratings on the SPP modes. Our work will pave the way to fully understanding the influence of incident angles on a detector’s response for applying the MIM-QWIP to focal plane arrays.

  20. Angular dependence of optical modes in metal-insulator-metal coupled quantum well infrared photodetector

    Directory of Open Access Journals (Sweden)

    YouLiang Jing

    2016-04-01

    Full Text Available We report the dependence of the near-field optical modes in metal-insulator-metal quantum well infrared photodetector (MIM-QWIP on the incident angles. Three optical modes are observed and attributed to the 2nd- and the 3rd-order surface plasmon polariton (SPP modes and the localized surface polariton (LSP mode. In addition to the observation of a responsivity enhancement of 14 times by the LSP mode, the varying pattern of the three modes against the incident angle are revealed, in which the LSP mode is fixed while the 2nd SPP mode splits into two branches and the 3rd SPP mode red-shifts. The detailed mechanisms are analyzed and numerically simulated. The results fit the experiments very well, demonstrating the wavevector coupling effect between the incident light and the metal gratings on the SPP modes. Our work will pave the way to fully understanding the influence of incident angles on a detector’s response for applying the MIM-QWIP to focal plane arrays.

  1. Improved Stress Reliability of Analog TiHfO Metal-Insulator-Metal Capacitors Using High-Work-Function Electrode

    Science.gov (United States)

    Cheng, Chun-Hu; Chiang, Kuo-Cheng; Pan, Han-Chang; Hsiao, Chien-Nan; Chou, Chang-Pin; McAlister, Sean P.; Chin, Albert

    2007-11-01

    We have studied the reliability of high-κ (κ ˜ 49) TixHf1-xO (x ˜ 0.67) metal-insulator-metal (MIM) capacitors after constant voltage stress induction. The use of a high-work-function Ni top electrode improves not only the leakage current, and temperature- and voltage-coefficients of capacitance, but also the long-term capacitance variation after stress induction.

  2. Low-temperature high magnetic field powder x-ray diffraction setup for field-induced structural phase transition studies from 2 to 300 K and at 0 to 8-T field

    Science.gov (United States)

    Shahee, Aga; Sharma, Shivani; Kumar, Dhirendra; Yadav, Poonam; Bhardwaj, Preeti; Ghodke, Nandkishor; Singh, Kiran; Lalla, N. P.; Chaddah, P.

    2016-10-01

    A low-temperature and high magnetic field powder x-ray diffractometer (XRD) has been developed at UGC-DAE CSR (UGC: University Grant Commission, DAE: Department of Atomic Energy, and CSR: Consortium for scientific research), Indore, India. The setup has been developed around an 18 kW rotating anode x-ray source delivering Cu-Kα x-rays coming from a vertical line source. It works in a symmetric θ-2θ parallel beam geometry. It consists of a liquid helium cryostat with an 8 T split-pair Nb-Ti superconducting magnet comprising two x-ray windows each covering an angular range of 65°. This is mounted on a non-magnetic type heavy duty goniometer equipped with all necessary motions along with data collection accessories. The incident x-ray beam has been made parallel using a parabolic multilayer mirror. The scattered x-ray is detected using a NaI detector through a 0.1° acceptance solar collimator. To control the motions of the goniometer, a computer programme has been developed. The wide-angle scattering data can be collected in a range of 2°-115° of 2θ with a resolution of ˜0.1°. The whole setup is tightly shielded for the scattered x-rays using a lead hutch. The functioning of the goniometer and the artifacts arising possibly due to the effect of stray magnetic field on the goniometer motions, on the x-ray source, and on the detector have been characterized by collecting powder XRD data of a National Institute of Standards and Technology certified standard reference material LaB6 (SRM-660b) and Si powder in zero-field and in-field conditions. Occurrence of field induced structural-phase transitions has been demonstrated on various samples like Pr0.5Sr0.5MnO3, Nd0.49Sr0.51MnO3-δ and La0.175Pr0.45Ca0.375MnO3 by collecting data in zero field cool and field cool conditions.

  3. Metal-insulator-metal diodes with sub-nanometre surface roughness for energy-harvesting applications

    KAUST Repository

    Khan, A.A.

    2017-07-27

    For ambient radio-frequency (RF) energy harvesting, the available power levels are quite low, and it is highly desirable that the rectifying diodes do not consume any power at all. Contrary to semiconducting diodes, a tunnelling diode – also known as a metal-insulator-metal (MIM) diode – can provide zero-bias rectification, provided the two metals have different work functions. This could result in a complete passive rectenna system. Despite great potential, MIM diodes have not been investigated much in the GHz-frequency regime due to challenging nano-fabrication requirements. In this work, we investigate zero-bias MIM diodes for RF energy-harvesting applications. We studied the surface roughness issue for the bottom metal of the MIM diode for various deposition techniques such as sputtering, atomic layer deposition (ALD) and electron-beam (e-beam) evaporation for crystalline metals as well as for an amorphous alloy, namely ZrCuAlNi. A surface roughness of sub-1nm has been achieved for both the crystalline metals as well as the amorphous alloy, which is vital for the reliable operation of the MIM diode. An MIM diode comprising of a Ti-ZnO-Pt combination yields a zero-bias responsivity of 0.25V−1 and a dynamic resistance of 1200Ω. Complete RF characterisation has been performed by integrating the MIM diode with a coplanar waveguide transmission line. The input impedance varies from 100Ω to 50Ω in the frequency range of between 2GHz and 10GHz, which can be easily matched to typical antenna impedances in this frequency range. Finally, a rectified DC voltage of 4.7mV is obtained for an incoming RF power of 0.4W at zero bias. These preliminary results of zero-bias rectification indicate that complete, passive rectennas (a rectifier and antenna combination) are feasible with further optimisation of MIM devices.

  4. Development of High-Performance Reflective Metal Insulation Through Optimized Sheet Plate Design

    Energy Technology Data Exchange (ETDEWEB)

    Eo, Min-hun; Lee, Sung-Myung; Jang, Kye-hwan; Kim, Won-Seok [BHI Co. Ltd., Haman (Korea, Republic of)

    2015-10-15

    Conservative insulation is especially difficult to apply to NPP facilities in consideration of operators' safety due to its characteristics of having unstable chemical and structural property, being easily degradable, and being able to produce harmful gases in the case of accidents and exposure to high temperature. Korean regulation organizations, together with the U.S., are considering the possibility of implementing a safety-enhanced technology of Reflective Metal Insulation (RMI) in order to solve safety problems such as sump clogging and ECC failure. RMI is made of stainless sheet plates with low emissivity and closed air spaces. The low emissivity in stainless steel blocks out thermal radiation, while the closed air spaces block out thermal conductivity and thermal convection. In this study, we made an analysis of the structure and shape of stainless sheet plates, the most important factor for the RMI design, by using Therm 7.3. Sheet plate design for maximizing insulating capacity of RMI was analyzed by Therm 7.3. The results are as follows: 1. In the case of an air layer with a thickness of 10mm or less, heat transfer by convection is completely blocked regardless of the heat flow direction. Therefore, when designing a sheet plate, heat transfer by radiation and heat conduction are the most important factors. 2. By minimizing the contact area between the stainless steel sheets, it is possible to minimize heat loss through conduction and, at the same time, maximize the radiation shielding effect in all areas. An increase in contact area causes a decrease in air gap, disallowing radiation shielding effect to take place.

  5. Experimental Studies of New GaAs Metal/Insulator/p-n+ Switches Using Low Temperature Oxide

    Directory of Open Access Journals (Sweden)

    K. F. Yarn

    2002-01-01

    grown at low temperature by a liquid phase chemical-enhanced oxide (LPECO with a thickness of 100 Å. A significant S-shaped negative differential resistance (NDR is shown to occur that originates from the regenerative feedback in a tunnel metal/insulator/semiconductor (MIS interface and p-n+ junction. The influence of epitaxial doping concentration on the switching and holding voltages is investigated. The switching voltages are found to be decreased when increasing the epitaxial doping concentration, while the holding voltages are almost kept constant. A high turn-off/turn-on resistance ratio up to 105 has been obtained.

  6. Perfect absorbers based on metal-insulator-metal structures in the visible region: a simple approach for practical applications

    Science.gov (United States)

    Kenanakis, G.; Mavidis, Ch. P.; Vasilaki, E.; Katsarakis, N.; Kafesaki, M.; Economou, E. N.; Soukoulis, C. M.

    2017-01-01

    Perfect absorbers based on metal-insulator-metal (MIM) structures are proposed and demonstrated, both theoretically and experimentally, in the visible region. The proposed structures may possess either sharp or broadband absorption peaks, by simply choosing a single layer of the proposed MIM structure or building several layers of them, while no nanofabrication steps or structure patterning are required, and thus can be easily made to cover a large area. The highly efficient absorption of the MIM structures is maintained for both TE and TM incident polarization, and for angles of incidence up to 75°, indicating that the proposed perfect absorbers can be potentially deployed for solar cells applications and optics.

  7. Modeling of all-optical even and odd parity generator circuits using metal-insulator-metal plasmonic waveguides

    Science.gov (United States)

    Singh, Lokendra; Bedi, Amna; Kumar, Santosh

    2017-01-01

    Plasmonic metal-insulator-metal (MIM) waveguides sustain excellent property of confining the surface plasmons up to a deep subwavelength scale. In this paper, linear and S-shaped MIM waveguides are cascaded together to design the model of Mach-Zehnder interferometer (MZI). Nonlinear material has been used for switching of light across its output ports. The structures of even and odd parity generators are projected by cascading the MZIs. Parity generator and checker circuit are used for error correction and detection in an optical communication system. Study and analysis of proposed designs are carried out by using the MATLAB simulation and finite-differencetime-domain (FDTD) method.

  8. Low leakage stoichiometric SrTiO{sub 3} dielectric for advanced metal-insulator-metal capacitors

    Energy Technology Data Exchange (ETDEWEB)

    Popovici, Mihaela; Kaczer, Ben; Redolfi, Augusto; Elshocht, Sven van; Jurczak, Malgorzata [imec Belgium, Leuven (Belgium); Afanas' ev, Valeri V. [Department of Physics and Astronomy, KU Leuven (Belgium); Sereni, Gabriele [DISMI, Universita degli Studi di Modena e Reggio Emilia, (Italy); Larcher, Luca [DISMI, Universita degli Studi di Modena e Reggio Emilia, (Italy); MDLab, Saint Christophe (Italy)

    2016-05-15

    Metal-insulator-metal capacitors (MIMCAP) with stoichiometric SrTiO{sub 3} dielectric were deposited stacking two strontium titanate (STO) layers, followed by intermixing the grain determining Sr-rich STO seed layer, with the Ti-rich STO top layer. The resulted stoichiometric SrTiO{sub 3} would have a structure with less defects as demonstrated by internal photoemission experiments. Consequently, the leakage current density is lower compared to Sr-rich STO which allow further equivalent oxide thickness downscaling. (copyright 2016 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  9. Model for continuous thermal metal to insulator transition

    Science.gov (United States)

    Jian, Chao-Ming; Bi, Zhen; Xu, Cenke

    2017-09-01

    We propose a d -dimensional interacting Majorana fermion model with quenched disorder, which gives us a continuous quantum phase transition between a diffusive thermal metal phase with a finite entropy density to an insulator phase with zero entropy density. This model is based on coupled Sachdev-Ye-Kitaev model clusters, and hence has a controlled large-N limit. The metal-insulator transition is accompanied by a spontaneous time-reversal symmetry breaking. We perform controlled calculations to show that the energy diffusion constant jumps to zero discontinuously at the metal-insulator transition, while the time-reversal symmetry-breaking order parameter increases continuously.

  10. Fano Resonance Based on Metal-Insulator-Metal Waveguide-Coupled Double Rectangular Cavities for Plasmonic Nanosensors

    Directory of Open Access Journals (Sweden)

    Zhidong Zhang

    2016-05-01

    Full Text Available A refractive index sensor based on metal-insulator-metal (MIM waveguides coupled double rectangular cavities is proposed and investigated numerically using the finite element method (FEM. The transmission properties and refractive index sensitivity of various configurations of the sensor are systematically investigated. An asymmetric Fano resonance lineshape is observed in the transmission spectra of the sensor, which is induced by the interference between a broad resonance mode in one rectangular and a narrow one in the other. The effect of various structural parameters on the Fano resonance and the refractive index sensitivity of the system based on Fano resonance is investigated. The proposed plasmonic refractive index sensor shows a maximum sensitivity of 596 nm/RIU.

  11. High-performance GaAs metal-insulator-semiconductor field-effect transistors enabled by self-assembled nanodielectrics

    Science.gov (United States)

    Lin, H. C.; Ye, P. D.; Xuan, Y.; Lu, G.; Facchetti, A.; Marks, T. J.

    2006-10-01

    High-performance GaAs metal-insulator-semiconductor field-effect-transistors (MISFETs) fabricated with very thin self-assembled organic nanodielectrics (SANDs), deposited from solution at room temperature, are demonstrated. A submicron gate-length depletion-mode n-channel GaAs MISFET with SAND thicknesses ranging from 5.5to16.5nm exhibit a gate leakage current density <10-5A/cm2 at a gate bias smaller than 3V, a maximum drain current of 370mA/mm at a forward gate bias of 2V, and a maximum intrinsic transconductance of 170mS/mm. The importance of appropriate GaAs surface chemistry treatments on SAND/GaAs interface properties is also presented. Application of SANDs to III-V compound semiconductors affords more opportunities to manipulate the complex III-V surface chemistry with broad materials options.

  12. Effect of Electric Field and Polarity on Light Emission in Metal-Insulator-Semiconductor Structure Thin-Film Electroluminescent Devices

    Science.gov (United States)

    Ohwaki, Jun-ichi; Kozawaguchi, Haruki; Tsujiyama, Bunjiro

    1983-01-01

    Changes in the emission intensities and spectra with applied electric fields in Metal-Insulator-Semiconductor (MIS) structure thin-film electroluminescent (TFEL) devices have been investigated using devices with stacked emitting layer structures, such as ITO/ZnS: Mn/ZnS: Tb/Sm2O3/Al. In MIS-TFEL devices, the emission distribution in the direction of the ZnS film thickness is nonhomogeneous. In particular, the emission intensity in the region near the ZnS-insulator interface increases with increasing applied voltage more than in the other region in the ZnS layer, when electrons exciting emission centers are accelerated from the insulator side. On the other hand, the emission is homogeneous at the opposite polarity. It is found that the emission color for stacked emitting layer MIS-TFEL devices can be modulated by changing the applied voltage.

  13. Mott-Hubbard transition in the mass-imbalanced Hubbard model

    Science.gov (United States)

    Philipp, Marie-Therese; Wallerberger, Markus; Gunacker, Patrik; Held, Karsten

    2017-06-01

    The mass-imbalanced Hubbard model represents a continuous evolution from the Hubbard to the Falicov-Kimball model. We employ dynamical mean field theory and study the paramagnetic metal-insulator transition, which has a very different nature for the two limiting models. Our results indicate that the metal-insulator transition rather resembles that of the Hubbard model as soon as a tiny hopping between the more localized fermions is switched on. At low temperatures we observe a first-order metal-insulator transition and a three peak structure. The width of the central peak is the same for the more and less mobile fermions when approaching the phase transition, which agrees with our expectation of a common Kondo temperature and phase transition for the two species.

  14. Gate-tunable phase transitions in thin flakes of 1T-TaS2

    Science.gov (United States)

    Yu, Yijun; Yang, Fangyuan; Lu, Xiu Fang; Yan, Ya Jun; Cho, Yong-Heum; Ma, Liguo; Niu, Xiaohai; Kim, Sejoong; Son, Young-Woo; Feng, Donglai; Li, Shiyan; Cheong, Sang-Wook; Chen, Xian Hui; Zhang, Yuanbo

    2015-03-01

    The ability to tune material properties using gating by electric fields is at the heart of modern electronic technology. It is also a driving force behind recent advances in two-dimensional systems, such as the observation of gate electric-field-induced superconductivity and metal-insulator transitions. Here, we describe an ionic field-effect transistor (termed an iFET), in which gate-controlled Li ion intercalation modulates the material properties of layered crystals of 1T-TaS2. The strong charge doping induced by the tunable ion intercalation alters the energetics of various charge-ordered states in 1T-TaS2 and produces a series of phase transitions in thin-flake samples with reduced dimensionality. We find that the charge-density wave states in 1T-TaS2 collapse in the two-dimensional limit at critical thicknesses. Meanwhile, at low temperatures, the ionic gating induces multiple phase transitions from Mott-insulator to metal in 1T-TaS2 thin flakes, with five orders of magnitude modulation in resistance, and superconductivity emerges in a textured charge-density wave state induced by ionic gating. Our method of gate-controlled intercalation opens up possibilities in searching for novel states of matter in the extreme charge-carrier-concentration limit.

  15. Metal-insulator transition in Mg-doped SrRuO{sub 3} thin films prepared by laser ablation

    Energy Technology Data Exchange (ETDEWEB)

    Crandles, D A; Yazdanian, Mohammad Mehdi; Razavi, F S [Department of Physics, Brock University, St Catharines, ON L2S 3A1 (Canada)

    2006-01-07

    Thin films of magnesium doped SrRuO{sub 3} (Mg-SRO) have been successfully prepared by laser ablation on SrTiO{sub 3} (100) substrates. The stoichiometry, structural, electrical and magnetic properties of the films depend on the substrate temperature (T{sub s}) and oxygen pressure (P{sub O{sub 2}}) during deposition. All Mg-SRO films are ferromagnetic, but the transport properties and remanent moments vary with T{sub s} and P{sub O{sub 2}}. Metallic films are produced for T{sub s} {>=} 700 deg. C whereas insulating films can be produced with T{sub s} = 500 deg. C with P{sub O{sub 2}}{>=}27 Pa. A correlation between lattice parameter, stoichiometry and transport properties has been discovered: the larger lattice parameter correlates with the decreased Ru content and more insulating samples. Insulating samples prepared at T{sub s} = 500 deg. C and P{sub O{sub 2}}{>=}27 Pa have stoichiometry close to the SrMg{sub 0.15}Ru{sub 0.85}O{sub 3} and are ferromagnetic Anderson insulators with transport properties consistent with variable range hopping.

  16. Phase fluctuations in a strongly disordered s-wave NbN superconductor close to the metal-insulator transition.

    Science.gov (United States)

    Mondal, Mintu; Kamlapure, Anand; Chand, Madhavi; Saraswat, Garima; Kumar, Sanjeev; Jesudasan, John; Benfatto, L; Tripathi, Vikram; Raychaudhuri, Pratap

    2011-01-28

    We explore the role of phase fluctuations in a three-dimensional s-wave superconductor, NbN, as we approach the critical disorder for destruction of the superconducting state. Close to critical disorder, we observe a finite gap in the electronic spectrum which persists at temperatures well above T(c). The superfluid density is strongly suppressed at low temperatures and evolves towards a linear-T variation at higher temperatures. These observations provide strong evidence that phase fluctuations play a central role in the formation of a pseudogap state in a disordered s-wave superconductor.

  17. Characterization of Metal-Insulator-Transition (MIT) Phase Change Materials (PCM) for Reconfigurable Components, Circuits, and Systems

    Science.gov (United States)

    2013-03-01

    sample doped with TiO2 as temperature is increased [38...resistance values can be tuned to provide a wide- band filter with a reconfigurable range of up to six-orders of magnitude. The MEMS based filter can...switch can be calculated using Equation 7: 827 7 where k is the spring constant defined in Equation 5, go is the initial gap between the cantilever

  18. Charge and spin diffusion on the metallic side of the metal-insulator transition: A self-consistent approach

    Science.gov (United States)

    Wellens, Thomas; Jalabert, Rodolfo A.

    2016-10-01

    We develop a self-consistent theory describing the spin and spatial electron diffusion in the impurity band of doped semiconductors under the effect of a weak spin-orbit coupling. The resulting low-temperature spin-relaxation time and diffusion coefficient are calculated within different schemes of the self-consistent framework. The simplest of these schemes qualitatively reproduces previous phenomenological developments, while more elaborate calculations provide corrections that approach the values obtained in numerical simulations. The results are universal for zinc-blende semiconductors with electron conductance in the impurity band, and thus they are able to account for the measured spin-relaxation times of materials with very different physical parameters. From a general point of view, our theory opens a new perspective for describing the hopping dynamics in random quantum networks.

  19. Metal-insulator transition with ferrimagnetic order in epitaxial thin films of spinel NiCo2O4

    Science.gov (United States)

    Silwal, Punam; Miao, Ludi; Stern, Ilan; Zhou, Xiaolan; Hu, Jin; Spinu, Leonard; Kim, Dae Ho; Talbayev, Diyar

    2014-03-01

    Spinel NiCo2O4 is attractive for various technological applications but is less studied partly because of the unavailability of NiCo2O4 single crystal or epitaxial thin film. We have grown high-quality crystalline epitaxial NiCo2O4 thin films on MgAl2O4 (001) substrates. The systematic investigation of the films grown at various temperatures reveals a strong correlation between the structural, magnetic, and electrical transport properties. The low-temperature grown films show metallic behavior with strong ferrimagnetic ordering while the high temperature grown films are insulating with suppressed magnetic order. In addition, these films show excellent transport and magnetic properties down to 2 unit-cell thickness. Our study of temperature- and growth-condition dependent optical conductivity provides further insight in the carrier transport of these films. We observed coherent band-like transport in both low- and high temperature grown films, whereas only thermally activated hopping conductivity was reported in previous studies. The confirmation of coherent band like transport provides a basis for further improving NiCo2O4 for the application as transparent conducting oxide.

  20. Real-space observation of metal-insulator transition at complex oxide heterointerface with cross-sectional STM

    Science.gov (United States)

    Chiu, Ya-Ping; Lin, Jheng-Cyuan; Thanh, Tra-Vu; Lin, Tai-Te; Huang, Po-Cheng; Huang, Bo-Chao; Lin, Jiunn-Yuan; Chu, Ying-Hao

    We report the direct observation of tunable electronic property through visible light at LaAlO3 / SrTiO3 (LAO/STO) complex oxide heterointerface using cross-sectional scanning tunneling microscopy and spectroscopy (XSTM/S). Many researches have shown that for the interface to be conducting, the thickness of LAO should be equal to or greater than the critical value 4 unit cells (u.c.). With LAO surface modification by Au clusters, interfacial two-dimensional electron gas presents a giant optical switching effect under visible light illuminated. In this study, through the interaction between photons and electrons system, a direct observation of the evolution of electronic structures from insulating to conducting has been revealed in the LAO (3u.c.)/STO model using the technique of cross-sectional scanning tunneling microscopy and spectroscopy. Results clearly reveal the changes in the built-in electric field in LAO and the band bending in the STO adjacent to the interface after light illumination. National Sun Yat-sen University, Taiwan; Academia Sinica, Taiwan.

  1. Magnetic and transport properties of amorphous GdxGe1-x alloys near the metal-insulator transition

    Science.gov (United States)

    Helgren, E.; Hellman, F.; Zeng, Li; Sinenian, N.; Islam, R.; Smith, David J.

    2007-11-01

    The temperature and field dependence of magnetization and conductivity of amorphous Ge doped with Gd (a-GdxGe1-x) has been measured for a wide range of x (0.08Weiss law and shows no significant dependence on composition. Conductivity measurements show that Gd causes localization of charge carriers below a characteristic temperature T* , which also marks the onset of significant negative magnetoresistance. Both T* and the magnitude of the MR are significantly lower in a-Gd-Ge than in comparable a-Gd-Si alloys. It is proposed that the large effects of the host matrix (Ge vs Si) are due to differences in both the band gap and dielectric constant, which cause changes in screening, thereby altering the effect of Gd magnetic moments on the localization of carriers and on the indirect mediated Gd-Gd exchange interactions.

  2. Late First-Row Transition-Metal Complexes Containing a 2-Pyridylmethyl Pendant-Armed 15-Membered Macrocyclic Ligand. Field-Induced Slow Magnetic Relaxation in a Seven-Coordinate Cobalt(II) Compound.

    Science.gov (United States)

    Antal, Peter; Drahoš, Bohuslav; Herchel, Radovan; Trávníček, Zdeněk

    2016-06-20

    The 2-pyridylmethyl N-pendant-armed heptadentate macrocyclic ligand {3,12-bis(2-methylpyridine)-3,12,18-triaza-6,9-dioxabicyclo[12.3.1]octadeca-1,14,16-triene = L} and [M(L)](ClO4)2 complexes, where M = Mn(II) (1), Fe(II) (2), Co(II) (3), Ni(II) (4), and Cu(II) (5), were prepared and thoroughly characterized, including elucidation of X-ray structures of all the compounds studied. The complexes 1-5 crystallize in non-centrosymmetric Sohncke space groups as racemic compounds. The coordination numbers of 7, 6 + 1, and 5 were found in complexes 1-3, 4, and 5, respectively, with a distorted pentagonal bipyramidal (1-4) or square pyramidal (5) geometry. On the basis of the magnetic susceptibility experiments, a large axial zero-field splitting (ZFS) was found for 2, 3, and 4 (D(Fe) = -7.4(2) cm(-1), D(Co) = 34(1) cm(-1), and D(Ni) = -12.8(1) cm(-1), respectively) together with a rhombic ZFS (E/D = 0.136(3)) for 4. Despite the easy plane anisotropy (D > 0, E/D = 0) in 3, the slow relaxation of the magnetization below 8 K was observed and analyzed either with Orbach relaxation mechanism (the relaxation time τ0 = 9.90 × 10(-10) s and spin reversal barrier Ueff = 24.3 K (16.9 cm(-1))) or with Raman relaxation mechanism (C = 2.12 × 10(-5) and n = 2.84). Therefore, compound 3 enlarges the small family of field-induced single-molecule magnets with pentagonal-bipyramidal chromophore. The cyclic voltammetry in acetonitrile revealed reversible redox processes in 1-3 and 5, except for the Ni(II) complex 4, where a quasi-reversible process was dominantly observed. Presence of the two 2-pyridylmethyl pendant arms in L with a stronger σ-donor/π-acceptor ability had a great impact on the properties of all the complexes (1-5), concretely: (i) strong pyridine-metal bonds provided slight axial compression of the coordination sphere, (ii) substantial changes in magnetic anisotropy, and (iii) stabilization of lower oxidation states.

  3. Mott transitions in a three-component Falicov-Kimball model: A slave boson mean-field study

    Science.gov (United States)

    Le, Duc-Anh; Tran, Minh-Tien

    2015-05-01

    Metal-insulator transitions in a three-component Falicov-Kimball model are investigated within the Kotliar-Ruckenstein slave boson mean-field approach. The model describes a mixture of two interacting fermion atom species loaded into an optical lattice at ultralow temperature. One species is two-component atoms, which can hop in the optical lattice, and the other is single-component atoms, which are localized. Different correlation-driven metal-insulator transitions are observed depending on the atom filling conditions and local interactions. These metal-insulator transitions are classified by the band renormalization factors and the double occupancies of the atom species. The filling conditions and the critical value of the local interactions for these metal-insulator transitions are also analytically established. The obtained results not only are in good agreement with the dynamical mean-field theory for the three-component Falicov-Kimball model but also clarify the nature and properties of the metal-insulator transitions in a simple physics picture.

  4. Non-ohmic behavior of metal-insulator granular thin films in low-field regime (eΔV ≪ kBT)

    Science.gov (United States)

    Boff, M. A. S.; Canto, B.; Mesquita, F.; Hinrichs, R.; Fraga, G. L. F.; Pereira, L. G.

    2016-10-01

    Non-ohmic behavior is not expected in metal-insulator granular systems in a low-field regime. There is no model to explain this behavior, even though it has been reported in several metal-insulator granular thin films (Fe-Al2O3, Co-Al2O3, and Ti-SiO2). In this paper, we show additional experimental results of Fe-SiO2 granular films and propose an explanation for the electrical properties of all above mentioned systems, based on Mott variable range hopping. The experimental results show that the localization length increases and the electrical resistance decreases with the increase of electrical potential or current. The non-ohmic behavior of the resistance and the increase of the localization length with increasing current are explained by the activation of new pathways for electrons in granular thin films that contain variable grain sizes and/or have different distances between grains.

  5. A highly efficient surface plasmon polaritons excitation achieved with a metal-coupled metal-insulator-metal waveguide

    Directory of Open Access Journals (Sweden)

    Hongyan Yang

    2014-12-01

    Full Text Available We propose a novel metal-coupled metal-insulator-metal (MC-MIM waveguide which can achieve a highly efficient surface plasmon polaritons (SPPs excitation. The MC-MIM waveguide is formed by inserting a thin metal film in the insulator of an MIM. The introduction of the metal film, functioning as an SPPs coupler, provides a space for the interaction between SPPs and a confined electromagnetic field of the intermediate metal surface, which makes energy change and phase transfer in the metal-dielectric interface, due to the joint action of incomplete electrostatic shielding effect and SPPs coupling. Impacts of the metal film with different materials and various thickness on SPPs excitation are investigated. It is shown that the highest efficient SPPs excitation is obtained when the gold film thickness is 60 nm. The effect of refractive index of upper and lower symmetric dielectric layer on SPPs excitation is also discussed. The result shows that the decay value of refractive index is 0.3. Our results indicate that this proposed MC-MIM waveguide may offer great potential in designing a new SPPs source.

  6. Electrical characterization of a-C:H as a dielectric material in metal/insulator/metal structures

    Energy Technology Data Exchange (ETDEWEB)

    Zuniga-I., C.; Kosarev, A.; Torres-J., A.; Rosales-Q., P.; Calleja-A., W.; Hidalga-W., F.J. de la; Malik, O. [Electronic' s Department, National Institute for Astrophysics, Optics, and Electronics, INAOE, Puebla (Mexico)

    2010-04-15

    The fabrication and electrical characterization of Metal-Insulator-Metal (MIM) structures, using a-C:H films as the insulating material, are presented in this work. These PECVD carbon films show a very low dielectric constant and a very high resistivity. The current conduction mechanisms were analyzed before and after the post deposition annealing in pure argon ambient at 400 C. For as-deposited films, the experimental J -U curves showed that under low biasing regime (vertical stroke U vertical stroke <8 V) the space charge limited current conduction is the main transport mechanism, whereas under higher biasing regime (vertical stroke U vertical stroke >8 V) the current transport is dominated by the Schottky mechanism. For annealed structures, under low and high biasing the ohmic and Schottky mechanisms were identified as the main processes for the electrical transport. Finally, we found that both parameters, the dielectric constant and resistivity, decrease slightly after the thermal annealing. (copyright 2010 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  7. Theoretical investigation of silicide Schottky barrier detector integrated in horizontal metal-insulator-silicon-insulator-metal nanoplasmonic slot waveguide.

    Science.gov (United States)

    Zhu, Shiyang; Lo, G Q; Kwong, D L

    2011-08-15

    An ultracompact integrated silicide Schottky barrier detector (SBD) is designed and theoretically investigated to electrically detect the surface plasmon polariton (SPP) propagating along horizontal metal-insulator-silicon-insulator-metal nanoplasmonic slot waveguides at the telecommunication wavelength of 1550 nm. An ultrathin silicide layer inserted between the silicon core and the insulator, which can be fabricated precisely using the well-developed self-aligned silicide process, absorbs the SPP power effectively if a suitable silicide is chosen. Moreover, the Schottky barrier height in the silicide-silicon-silicide configuration can be tuned substantially by the external voltage through the Schottky effect owing to the very narrow silicon core. For a TaSi(2) detector with optimized dimensions, numerical simulation predicts responsivity of ~0.07 A/W, speed of ~60 GHz, dark current of ~66 nA at room temperature, and minimum detectable power of ~-29 dBm. The design also suggests that the device's size can be reduced and the overall performances will be further improved if a silicide with smaller permittivity is used.

  8. Fabrication of Buried Co-Planar Metal-Insulator-Metal Nanojunctions with a Gap Lower than 10nm

    Science.gov (United States)

    Rousset, V.; Joachim, C.; Itoua, S.; Rousset, B.; Fabre, N.

    1995-12-01

    An improvement of a process to fabricate co-planar metal-insulator-metal nanojunctions is presented to reach a gap length much lower than 10 nm using a 20 keV e-beam and an AuPd lift-off. The electrodes of the nanojunction are less than 100 nm in width and are buried in the SiO2 substrate. For the 8 nm nanojunctions, the gap is still filled with SiO2 if care is taken about the SiO2 etching step of the process. Un procédé de fabrication est proposé pour obtenir des nanojonctions métal-isolant-métal co-planaires d'une largeur d'isolant bien inférieure à 10nm en utilisant un masqueur électronique à 20keV et un “lift-off” à l'or-palladium. Les électrodes de la nanojonction enterrées dans la silice ont une largeur de moins de 100nm et sont distantes de 8nm. En optimisant l'étape de sous gravure, il est possible de conserver de la silice comme isolant entre les électrodes.

  9. Photoresponse of the In0.3Ga0.7N metal-insulator-semiconductor photodetectors

    Institute of Scientific and Technical Information of China (English)

    Zhou Jian-Jun; Zheng You-Dou; Wen Bo; Jiang Ruo-Lian; Liu Cheng-Xiang; Ji Xiao-Li; Xie Zi-Li; Chen Dun-Jun; Han Ping; Zhang Rong

    2007-01-01

    In0.3Ga0.7N metal-insulator-semiconductor (MIS) and metal-semiconductor (MS) surface barrier photodetectors have been fabricated. The In0.3Ga0.7N epilayers were grown on sapphire by metalorganic chemical vapour deposition(MOCVD). The photoresponse and reverse current-voltage characteristics of the In0.3Ga0.7N MIS and MS photodetectors were measured. A best zero bias responsivity of 0.18 A/W at 450 nm is obtained for the In0.3Ga0.7N MIS photodetector with 10 nm Si3N4 insulator layer, which is more than ten times higher than the In0.3Ga0.7N MS photodetector. The reason is attributed to the decrease of the interface states and increase of surface barrier height by the inserted insulator. The influence of the thickness of the Si3N4 insulator layer on the photoresponsivity of the MIS photodetector is also discussed.

  10. Compact all-optical interferometric logic gates based on one-dimensional metal-insulator-metal structures

    Science.gov (United States)

    Bian, Yusheng; Gong, Qihuang

    2014-02-01

    The whole set of fundamental all-optical logic gates is realized theoretically using a multi-channel configuration based on one-dimensional (1D) metal-insulator-metal (MIM) structures by leveraging the linear interference between surface plasmon polariton modes. The working principle and conditions for different logic functions are analyzed and demonstrated numerically by means of the finite element method. In contrast to most of the previous studies that require more than one type of configuration to achieve different logic functions, a single geometry with fixed physical dimensions can realize all fundamental functions in our case studies. It is shown that by switching the optical signals to different input channels, the presented device can realize simple logic functions such as OR, AND and XOR. By adding signal in the control channel, more functions including NOT, XNOR, NAND and NOR can be implemented. For these considered logic functions, high intensity contrast ratios between Boolean logic states "1" and "0" can be achieved at the telecom wavelength. The presented all-optical logic device is simple, compact and efficient. Moreover, the proposed scheme can be applied to many other nano-photonic logic devices as well, thereby potentially offering useful guidelines for their designs and further applications in on-chip optical computing and optical interconnection networks.

  11. Electrostatic analysis of n-doped SrTiO{sub 3} metal-insulator-semiconductor systems

    Energy Technology Data Exchange (ETDEWEB)

    Kamerbeek, A. M., E-mail: a.m.kamerbeek@rug.nl; Banerjee, T. [Physics of Nanodevices, Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, 9747 AG Groningen (Netherlands); Hueting, R. J. E. [Semiconductor Components, MESA+ Institute for Nanotechnology, University of Twente, 7500 AE Enschede (Netherlands)

    2015-12-14

    Electron doped SrTiO{sub 3}, a complex-oxide semiconductor, possesses novel electronic properties due to its strong temperature and electric-field dependent permittivity. Due to the high permittivity, metal/n-SrTiO{sub 3} systems show reasonably strong rectification even when SrTiO{sub 3} is degenerately doped. Our experiments show that the insertion of a sub nanometer layer of AlO{sub x} in between the metal and n-SrTiO{sub 3} interface leads to a dramatic reduction of the Schottky barrier height (from around 0.90 V to 0.25 V). This reduces the interface resistivity by 4 orders of magnitude. The derived electrostatic analysis of the metal-insulator-semiconductor (n-SrTiO{sub 3}) system is consistent with this trend. When compared with a Si based MIS system, the change is much larger and mainly governed by the high permittivity of SrTiO{sub 3}. The non-linear permittivity of n-SrTiO{sub 3} leads to unconventional properties such as a temperature dependent surface potential non-existent for semiconductors with linear permittivity such as Si. This allows tuning of the interfacial band alignment, and consequently the Schottky barrier height, in a much more drastic way than in conventional semiconductors.

  12. Control of normally on/off characteristics in hydrogenated diamond metal-insulator-semiconductor field-effect transistors

    Science.gov (United States)

    Liu, J. W.; Liao, M. Y.; Imura, M.; Matsumoto, T.; Shibata, N.; Ikuhara, Y.; Koide, Y.

    2015-09-01

    Normally on/off operation in hydrogenated diamond (H-diamond) metal-insulator-semiconductor field-effect transistors (MISFETs) is reproducibly controlled by annealing at 180 °C. The transfer characteristics of the MISFETs reveal that the threshold gate voltage changes from 0.8 ± 0.1 to -0.5 ± 0.1 V after annealing, which indicates the MISFETs switch from normally on to normally off operation. Annealing also shifts the flat-band voltage in the capacitance-voltage curve of MIS capacitors from zero to -0.47 V. The mechanism behind the switch of normally on/off characteristics induced by annealing is explained by a change of transfer doping as follows. Adsorbed acceptors at the insulator/H-diamond interface allow the holes to accumulate in the H-diamond channel layer, so the MISFETs before annealing show normally on characteristics. Annealing causes loss of the adsorbed acceptors or provides compensatory positive charge in the insulator oxide, so the hole density in the H-diamond channel layer decreases markedly, and the MISFETs show normally off characteristics.

  13. Schottky barrier height of Ni/TiO2/4H-SiC metal-insulator-semiconductor diodes

    Science.gov (United States)

    Kaufmann, Ivan R.; Pereira, Marcelo B.; Boudinov, Henri I.

    2015-12-01

    Ni/TiO2/4H-SiC diodes were analysed through measurements of current-voltage curves varying the temperature. The Schottky Barrier Height (SBH) which increased with temperature was studied by simulation of the Thermionic Emission Model, considering Ni/SiC Schottky structures with an insulator layer between the metal and semiconductor. This model shows that a new method of calculation should be applied to diodes that have a metal-insulator-semiconductor structure. Misleading results for SBH are obtained if the thin insulator layer is not considered. When applying the suggested method to the Ni/TiO2/4H-SiC diodes it was necessary to consider not only the deposited TiO2 layer, but also a second dielectric layer of native SiCxOy at the surface of SiC. By measuring I-V-T curves for two samples with different thicknesses of TiO2, the suggested method allows one to estimate the thicknesses of both dielectric layers: TiO2 and SiOxCy.

  14. Lateral amorphous selenium metal-insulator-semiconductor-insulator-metal photodetectors using ultrathin dielectric blocking layers for dark current suppression

    Science.gov (United States)

    Chang, Cheng-Yi; Pan, Fu-Ming; Lin, Jian-Siang; Yu, Tung-Yuan; Li, Yi-Ming; Chen, Chieh-Yang

    2016-12-01

    We fabricated amorphous selenium (a-Se) photodetectors with a lateral metal-insulator-semiconductor-insulator-metal (MISIM) device structure. Thermal aluminum oxide, plasma-enhanced chemical vapor deposited silicon nitride, and thermal atomic layer deposited (ALD) aluminum oxide and hafnium oxide (ALD-HfO2) were used as the electron and hole blocking layers of the MISIM photodetectors for dark current suppression. A reduction in the dark current by three orders of magnitude can be achieved at electric fields between 10 and 30 V/μm. The effective dark current suppression is primarily ascribed to electric field lowering in the dielectric layers as a result of charge trapping in deep levels. Photogenerated carriers in the a-Se layer can be transported across the blocking layers to the Al electrodes via Fowler-Nordheim tunneling because a high electric field develops in the ultrathin dielectric layers under illumination. Since the a-Se MISIM photodetectors have a very low dark current without significant degradation in the photoresponse, the signal contrast is greatly improved. The MISIM photodetector with the ALD-HfO2 blocking layer has an optimal signal contrast more than 500 times the contrast of the photodetector without a blocking layer at 15 V/μm.

  15. Resistive switching in a metal-insulator-metal device with γ-APTES as the insulator layer

    Science.gov (United States)

    Lin, Jing-Jenn; Lin, Shih-Hung; Wu, You-Lin

    2017-10-01

    Gamma-aminopropyltriethoxysilane (γ-APTES) is an organosilane material commonly used for biomedical sensing. Sensors with a γ-APTES surface layer have been reported for use in pH, DNA, and cell detection. However, no application of γ-APTES on resistive switching random access memory (RRAM) devices has yet been reported. In this paper, we report, for the first time, the resistive switching characteristics of using γ-APTES as the insulator layer in an RRAM device. The resistive switching of the γ-APTES layer embedded with ZnO nanoparticles is also investigated in this work. A unipolar resistive switching characteristic is found when the γ-APTES is employed as an insulator layer in a device with a metal-insulator-metal (MIM) structure. The stability and reliability of the resistive switching characteristics of the device can be improved after adding zinc oxide (ZnO) nanoparticles at the expense of reducing the ratio of the resistance of a high-resistance state (RHRS) to the resistance of a low-resistance state (RLRS).

  16. Theory of singlet-ground-state magnetism. Application to field-induced transitions in CsFeCl3 and CsFeBr3

    DEFF Research Database (Denmark)

    Lindgård, P.-A.; Schmid, B.

    1993-01-01

    the experimental data can be excellently described by the self-consistent random-phase approximation results. For magnetic fields near the critical magnetic field only qualitative conclusions can be obtained. Numerical results for the critical scattering, the correlation lengths, and the specific heat, which....... A sophisticated numerical and graphical method leads to a self-consistent determination of the induced magnetization and the quadrupole moment as well as to the determination of the excitation spectrum for CsFeBr3 and CsFeCl3 as a function of the magnetic field. For magnetic fields below the phase transition...

  17. Structural phase stability and electric field induced relaxor–ferroelectric phase transition in (1 − x)(Bi{sub 0.5}Na{sub 0.5})TiO{sub 3}–xBaTiO{sub 3} ceramics

    Energy Technology Data Exchange (ETDEWEB)

    Anthoniappen, J., E-mail: jesusvd@gmail.com [Graduate Institute of Applied Science and Engineering, Fu Jen Catholic University, New Taipei City 24205, Taiwan (China); Department of Physics, University of San Carlos, Cebu City 6000 (Philippines); Tu, C.S. [Graduate Institute of Applied Science and Engineering, Fu Jen Catholic University, New Taipei City 24205, Taiwan (China); Department of Physics, Fu Jen Catholic University, New Taipei City 24205, Taiwan (China); Chen, P.-Y. [Department of Mechanical Engineering, Ming-Chi University of Technology, New Taipei City 24301, Taiwan (China); Chen, C.-S. [Department of Mechanical Engineering, Hwa-Hsia Institute of Technology, New Taipei City 23567, Taiwan (China); Chiu, S.-J.; Lee, H.-Y. [National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan (China); Ting, Yi; Wang, S.-F. [Department of Physics, Fu Jen Catholic University, New Taipei City 24205, Taiwan (China); Chai, C.-K. [Department of Mechanical Engineering, Ming-Chi University of Technology, New Taipei City 24301, Taiwan (China)

    2015-01-05

    Highlights: • The well-known MPB compositions of [(1 − x)(Bi{sub 0.5}Na{sub 0.5})TiO{sub 3}–xBaTiO{sub 3}] (x = 0.06, 0.07 and 0.075) show a transition sequence of rhombohedral + tetragonal − tetragonal − cubic phases as a function of temperature. Functionally important two-phase coexists from room temperature to 200 °C. • The frequency-dispersion anomaly at lower temperatures indicates a progressive transition from ferroelectric to relaxor state upon heating. Therefore, phase coexistence plays a vital role in relaxor ferroelectric behavior among BNT–BT compositions. • The non-ergodic relaxor phase can be transformed into ferroelectric phase by dc poling field. - Abstract: Structure, phase transition, and dielectric relaxor behavior have been investigated in morphotropic phase boundary compositions of (1 − x)(Bi{sub 0.5}Na{sub 0.5})TiO{sub 3}-xBaTiO{sub 3} ceramics for x = 0.06, 0.07, and 0.075. In-situ structural thermal stability has been analyzed by using high-resolution synchrotron X-ray diffraction as a function of temperature. A transition sequence of rhombohedral + tetragonal − tetragonal − cubic phases is observed upon heating. The “rhombohedral + tetragonal” indicates a coexistence of rhombohedral R3c and tetragonal P4bm phases. The two-phase coexistence extends from room temperature to 200 °C. Zero-field dielectric permittivity reveals a frequency dispersion at low temperature region (T < T{sub m}) and polar nanoregions below Burns temperature (T{sub B}). The two-phase coexistence plays a vital role for frequency dispersion below T{sub m}. Dielectric spectra of pre-poled samples reveal a field-induced ferroelectric−relaxor phase transition at depolarization temperature T{sub d}.

  18. Fabrication and Characterization of ZnO Langmuir-Blodgett Film and Its Use in Metal-Insulator-Metal Tunnel Diode.

    Science.gov (United States)

    Azad, Ibrahim; Ram, Manoj K; Goswami, D Yogi; Stefanakos, Elias

    2016-08-23

    Metal-insulator-metal tunnel diodes have great potential for use in infrared detection and energy harvesting applications. The quantum based tunneling mechanism of electrons in MIM (metal-insulator-metal) or MIIM (metal-insulator-insulator-metal) diodes can facilitate rectification at THz frequencies. In this study, the required nanometer thin insulating layer (I) in the MIM diode structure was fabricated using the Langmuir-Blodgett technique. The zinc stearate LB film was deposited on Au/Cr coated quartz, FTO, and silicon substrates, and then heat treated by varying the temperature from 100 to 550 °C to obtain nanometer thin ZnO layers. The thin films were characterized by XRD, AFM, FTIR, and cyclic voltammetry methods. The final MIM structure was fabricated by depositing chromium/nickel over the ZnO on Au/Cr film. The current voltage (I-V) characteristics of the diode showed that the conduction mechanism is electron tunneling through the thin insulating layer. The sensitivity of the diodes was as high as 32 V(-1). The diode resistance was ∼80 Ω (at a bias voltage of 0.78 V), and the rectification ratio at that bias point was about 12 (for a voltage swing of ±200 mV). The diode response exhibited significant nonlinearity and high asymmetry at the bias point, very desirable diode performance parameters for IR detection applications.

  19. Glassy Behavior of Electrons as a Precursor to the Localization Transition

    OpenAIRE

    Dobrosavljevic, V.; Pastor, A. A.

    2003-01-01

    A theoretical model is presented, describing the glassy freezing of electrons in the vicinity of disorder driven metal-insulator transitions. Our results indicate that the onset of glassy dynamics should emerge before the localization transition is reached, thus predicting the existence of an intermediate metallic glass phase between the normal metal and the insulator.

  20. Mott-Hubbard transition in the mass-imbalanced Hubbard model

    OpenAIRE

    Philipp, Marie-Therese; Wallerberger, Markus; Gunacker, Patrik; Held, Karsten

    2016-01-01

    The mass-imbalanced Hubbard model represents a continuous evolution from the Hubbard to the Falicov-Kimball model. We employ dynamical mean field theory and study the paramagnetic metal-insulator transition, which has a very different nature for the two limiting models. Our results indicate that the metal-insulator transition rather resembles that of the Hubbard model as soon as a tiny hopping between the more localized fermions is switched on. At low temperatures we observe a first-order met...

  1. Investigation of the impact of insulator material on the performance of dissimilar electrode metal-insulator-metal diodes

    Science.gov (United States)

    Alimardani, Nasir; King, Sean W.; French, Benjamin L.; Tan, Cheng; Lampert, Benjamin P.; Conley, John F.

    2014-07-01

    The performance of thin film metal-insulator-metal (MIM) diodes is investigated for a variety of large and small electron affinity insulators using ultrasmooth amorphous metal as the bottom electrode. Nb2O5, Ta2O5, ZrO2, HfO2, Al2O3, and SiO2 amorphous insulators are deposited via atomic layer deposition (ALD). Reflection electron energy loss spectroscopy (REELS) is utilized to measure the band-gap energy (EG) and energy position of intrinsic sub-gap defect states for each insulator. EG of as-deposited ALD insulators are found to be Nb2O5 = 3.8 eV, Ta2O5 = 4.4 eV, ZrO2 = 5.4 eV, HfO2 = 5.6 eV, Al2O3 = 6.4 eV, and SiO2 = 8.8 eV with uncertainty of ±0.2 eV. Current vs. voltage asymmetry, non-linearity, turn-on voltage, and dominant conduction mechanisms are compared. Al2O3 and SiO2 are found to operate based on Fowler-Nordheim tunneling. Al2O3 shows the highest asymmetry. ZrO2, Nb2O5, and Ta2O5 based diodes are found to be dominated by Frenkel-Poole emission at large biases and exhibit lower asymmetry. The electrically estimated trap energy levels for defects that dominate Frenkel-Poole conduction are found to be consistent with the energy levels of surface oxygen vacancy defects observed in REELS measurements. For HfO2, conduction is found to be a mix of trap assisted tunneling and Frenkel-Poole emission. Insulator selection criteria in regards to MIM diodes applications are discussed.

  2. Role of microstructures on the M1-M2 phase transition in epitaxial VO2 thin films

    Science.gov (United States)

    Ji, Yanda; Zhang, Yin; Gao, Min; Yuan, Zhen; Xia, Yudong; Jin, Changqing; Tao, Bowan; Chen, Chonglin; Jia, Quanxi; Lin, Yuan

    2014-05-01

    Vanadium dioxide (VO2) with its unique sharp resistivity change at the metal-insulator transition (MIT) has been extensively considered for the near-future terahertz/infrared devices and energy harvesting systems. Controlling the epitaxial quality and microstructures of vanadium dioxide thin films and understanding the metal-insulator transition behaviors are therefore critical to novel device development. The metal-insulator transition behaviors of the epitaxial vanadium dioxide thin films deposited on Al2O3 (0001) substrates were systematically studied by characterizing the temperature dependency of both Raman spectrum and Fourier transform infrared spectroscopy. Our findings on the correlation between the nucleation dynamics of intermediate monoclinic (M2) phase with microstructures will open a new avenue for the design and integration of advanced heterostructures with controllable multifunctionalities for sensing and imaging system applications.

  3. Electrical properties and transport mechanisms of Au/Ba0.6Sr0.4TiO3/GaN metal-insulator-semiconductor (MIS) diode at high temperature range

    Science.gov (United States)

    Rajagopal Reddy, V.

    2016-05-01

    The electrical and transport mechanisms of a fabricated Au/Ba0.6Sr0.4TiO3 (BST)/GaN metal-insulator-semiconductor (MIS) diode have been studied in the temperature range of 280-430 K by current-voltage ( I- V) and capacitance-voltage ( C- V) measurements. The barrier heights (BHs) of the Au/BST/GaN MIS diode are found to be 0.85 eV ( I- V)/1.35 ( C- V) at 280 K and 1.14 eV ( I- V)/1.17 ( C- V) at 430 K. The series resistance ( R S) values determined by Cheung's functions are in good agreement with each other. The difference between BHs estimated by I- V and C- V methods are also discussed. Results show that the estimated interface state density ( N SS) of MIS diode decreases with an increase in temperature. Observations have indicated that the BH increases whereas ideality factor R S and N SS decreases with increasing temperature. Results have demonstrated that the reverse leakage current is dominated by Poole-Frenkel emission at temperatures of 280-340 K and by Schottky emission at temperatures of 370-430 K. It is also noted that there is a transition of the conduction mechanism in Au/BST/GaN MIS diode from Poole-Frenkel to Schottky emission at temperatures of 340-370 K.

  4. Mott transitions in three-component Falicov-Kimball model

    Science.gov (United States)

    Nguyen, Duong-Bo; Tran, Minh-Tien

    2013-01-01

    Metal-insulator transitions are studied within a three-component Falicov-Kimball model, which mimics a mixture of one-component and two-component fermionic particles with local repulsive interactions in optical lattices. Within the model, the two-component fermionic particles are able to hop in the lattice, while the one-component fermionic particles are localized. The model is studied by using the dynamical mean-field theory with exact diagonalization. Its homogeneous solutions establish Mott transitions for both commensurate and incommensurate fillings between one-third and two-thirds. At commensurate one-third and two-thirds fillings, the Mott transition occurs for any density of hopping particles, while at incommensurate fillings, the Mott transition can occur only for density one-half of hopping particles. At half-filling, depending on the repulsive interactions, the reentrant effect of the Mott insulator is observed. As increasing local interaction of hopping particles, the first insulator-metal transition is continuous, whereas the second metal-insulator transition is discontinuous. The second metal-insulator transition crosses a finite region where both metallic and insulating phase coexist. At third-filling, the Mott transition is established only for strong repulsive interactions. A phase separation occurs together with the phase transition.

  5. Conduction and rectification in NbO{sub x}- and NiO-based metal-insulator-metal diodes

    Energy Technology Data Exchange (ETDEWEB)

    Osgood, Richard M., E-mail: richard.m.osgood.civ@mail.mil; Giardini, Stephen; Carlson, Joel [US Army Natick Soldier Research Development and Engineering Center (NSRDEC), 15 General Greene Ave., Natick, Massachusetts 01760 (United States); Periasamy, Prakash; Guthrey, Harvey; O' Hayre, Ryan [Department of Metallurgical and Materials Engineering, Colorado School of Mines, Golden, Colorado 80401 (United States); Chin, Matthew; Nichols, Barbara; Dubey, Madan [RF and Electronics Division, US Army Research Laboratory, Adelphi, Maryland 20783 (United States); Fernandes, Gustavo; Kim, Jin Ho; Xu, Jimmy [Division of Engineering, Brown University, Box D, Providence, Rhode Island 02912 (United States); Parilla, Philip; Berry, Joseph; Ginley, David [National Renewable Energy Laboratory, Golden, Colorado 80401 (United States)

    2016-09-15

    Conduction and rectification in nanoantenna-coupled NbO{sub x}- and NiO-based metal-insulator-metal (MIM) diodes (“nanorectennas”) are studied by comparing new theoretical predictions with the measured response of nanorectenna arrays. A new quantum mechanical model is reported and agrees with measurements of current–voltage (I–V) curves, over 10 orders of magnitude in current density, from [NbO{sub x}(native)-Nb{sub 2}O{sub 5}]- and NiO-based samples with oxide thicknesses in the range of 5–36 nm. The model, which introduces new physics and features, including temperature, electron effective mass, and image potential effects using the pseudobarrier technique, improves upon widely used earlier models, calculates the MIM diode's I–V curve, and predicts quantitatively the rectification responsivity of high frequency voltages generated in a coupled nanoantenna array by visible/near-infrared light. The model applies both at the higher frequencies, when high-energy photons are incident, and at lower frequencies, when the formula for classical rectification, involving derivatives of the I–V curve, may be used. The rectified low-frequency direct current is well-predicted in this work's model, but not by fitting the experimentally measured I–V curve with a polynomial or by using the older Simmons model (as shown herein). By fitting the measured I–V curves with our model, the barrier heights in Nb-(NbO{sub x}(native)-Nb{sub 2}O{sub 5})-Pt and Ni-NiO-Ti/Ag diodes are found to be 0.41/0.77 and 0.38/0.39 eV, respectively, similar to literature reports, but with effective mass much lower than the free space value. The NbO{sub x} (native)-Nb{sub 2}O{sub 5} dielectric properties improve, and the effective Pt-Nb{sub 2}O{sub 5} barrier height increases as the oxide thickness increases. An observation of direct current of ∼4 nA for normally incident, focused 514 nm continuous wave laser beams are reported, similar in magnitude to recent reports

  6. Room-temperature electrically pumped near-infrared random lasing from high-quality m-plane ZnO-based metal-insulator-semiconductor devices

    OpenAIRE

    2015-01-01

    Epitaxial m-plane ZnO thin films have been deposited on m-plane sapphire substrates at a low temperature of 200°C by atomic layer deposition. A 90° in-plane rotation is observed between the m-plane ZnO thin films and the sapphire substrates. Moreover, the residual strain along the ZnO [−12-10] direction is released. To fabricate metal-insulator-semiconductor devices, a 50-nm Al2O3 thin film is deposited on the m-plane ZnO thin films. It is interesting to observe the near-infrared random lasin...

  7. Analysis of the electroluminescence features of silicon metal-insulator-semiconductor structures as a tool for diagnostics of the injection properties of a dielectric layer

    Science.gov (United States)

    Illarionov, Yu. Yu.; Vexler, M. I.; Isakov, D.; Fedorov, V. V.; Sing, Yew Kwang

    2013-10-01

    A technique for diagnostics of the injection properties of thin dielectric layers based on analysis of the data on silicon electroluminescence in a metal-insulator-semiconductor structure is proposed. The possibility of applying this technique to control the electron injection energy (in particular, when the barrier parameters are poorly known) is demonstrated by the example of samples with CaF2 and HfO2/SiO2. The results obtained are important for application of the insulators under study in microelectronic devices.

  8. Non-volatile ferroelastic switching of the Verwey transition and resistivity of epitaxial Fe3O4/PMN-PT (011).

    Science.gov (United States)

    Liu, Ming; Hoffman, Jason; Wang, Jing; Zhang, Jinxing; Nelson-Cheeseman, Brittany; Bhattacharya, Anand

    2013-01-01

    A central goal of electronics based on correlated materials or 'Mottronics' is the ability to switch between distinct collective states with a control voltage. Small changes in structure and charge density near a transition can tip the balance between competing phases, leading to dramatic changes in electronic and magnetic properties. In this work, we demonstrate that an electric field induced two-step ferroelastic switching pathway in (011) oriented 0.71Pb(Mg1/3Nb2/3)O3-0.29PbTiO3 (PMN-PT) substrates can be used to tune the Verwey metal-insulator transition in epitaxial Fe3O4 films in a stable and reversible manner. We also observe robust non-volatile resistance switching in Fe3O4 up to room temperature, driven by ferroelastic strain. These results provides a framework for realizing non-volatile and reversible tuning of order parameters coupled to lattice-strain in epitaxial oxide heterostructures over a broad range of temperatures, with potential device applications.

  9. Analysis of Heat Transfer Characteristics Based on Design Factors for Determining the Internal Geometry of Metal Insulation in Nuclear Power Plant

    Energy Technology Data Exchange (ETDEWEB)

    Song, Ki O; Yu, Jeong Ho; Lee, Tae Ho; Jeon, Hyun Ik; Ha, Seung Woo; Cho, Sun Young [KLES Inc., Seoul (Korea, Republic of)

    2015-11-15

    A heat insulating material used in the industrial site normally derives its heat insulating performance by using a low thermal conductivity material such as glass fiber. In case of the metal insulation for nuclear power plant, in contrast, only TP 304 stainless steel foil having high thermal conductivity is the only acceptable material. So, it is required to approach in structural aspect to ensure the insulation performance. In this study, the design factors related to the metal insulation internal structure were determined considering the three modes of heat transfer, i.e., conduction, convection, and radiation. The analysis of heat flow was used to understand the ratio of the heat transfer from each factor to the overall heat transfer from all the factors. Based on this study, in order to minimize the convection phenomenon caused by the internal insulation, a multiple foil was inserted in the insulation. The increase in the conduction heat transfer rate was compared, and the insulation performance under the three modes of heat transfer was analyzed in order to determine the internal geometry.

  10. Analysis of heat transfer characteristics based on design factors for determining the internal geometry of metal insulation in nuclear power plant

    Energy Technology Data Exchange (ETDEWEB)

    Song, Ki O; Yu, Jeong Ho; Lee, Tae Ho; Jeon, Hyun Ik; Ha, Seung Woo; Cho, Sun Young [KLES Inc., Daejeon (Korea, Republic of)

    2015-11-15

    A heat insulating material used in the industrial site normally derives its heat insulating performance by using a low thermal conductivity material such as glass fiber. In case of the metal insulation for nuclear power plant, in contrast, only TP 304 stainless steel foil having high thermal conductivity is the only acceptable material. So, it is required to approach in structural aspect to ensure the insulation performance. In this study, the design factors related to the metal insulation internal structure were determined considering the three modes of heat transfer, i.e., conduction, convection, and radiation. The analysis of heat flow was used to understand the ratio of the heat transfer from each factor to the overall heat transfer from all the factors. Based on this study, in order to minimize the convection phenomenon caused by the internal insulation, a multiple foil was inserted in the insulation. The increase in the conduction heat transfer rate was compared, and the insulation performance under the three modes of heat transfer was analyzed in order to determine the internal geometry.

  11. The electrical characteristics of a 4H-silicon carbide metal-insulator-semiconductor structure with Al2O3 as the gate dielectric

    Institute of Scientific and Technical Information of China (English)

    Liu Li; Yang Yin-Tang; Ma Xiao-Hua

    2011-01-01

    A 4H-silicon carbide metal-insulator-semiconductor structure with ultra-thin Al2O3 as the gate dielectric,deposited by atomic layer deposition on the epitaxial layer of a 4H-SiC (0001) 8(0)N-/N+ substrate,has been fabricated.The experimental results indicate that the prepared ultra-thin Al2O3 gate dielectric exhibits good physical and electrical characteristics,including a high breakdown electrical field of 25 MV/cm,excellent interface properties (1 × 1014 cm-2)and low gate-leakage current (IG =1 × 10-3 A/cm-2(o)Eox =8 MV/cm).Analysis of the current conduction mechanism on the deposited Al2O3 gate dielectric was also systematically performed.The confirmed conduction mechanisms consisted of Fowler-Nordheim (FN) tunneling,the Frenkel-Poole mechanism,direct tunneling and Schottky emission,and the dominant current conduction mechanism depends on the applied electrical field.When the gate leakage current mechanism is dominated by FN tunneling,the barrier height of SiC/Al2O3 is 1.4 eV,which can meet the requirements of silicon carbide metal-insulator-semiconductor transistor devices.

  12. Charge rearrangement in magnetite: from magnetic field induced easy axis switching to femtoseconds electronic processes

    Science.gov (United States)

    Kąkol, Z.; Kozłowski, A.; Kołodziej, T.; Przewoźnik, J.

    2015-02-01

    Magnetite is the oldest magnet and the first material where the concept of a strong correlations driven metal-insulator transition was suggested and found at TV = 124 K in the so-called Verwey phase transformation. Recently, the structure below TV was solved revealing subtle electronic structure in the form of trimeron lattice that, according to yet another recent communication, may be switched within femtosecond range. In this review article, we argue that the same change of trimeron lattice can be achieved by a magnetic field, in the phenomenon called the easy axis switching. The results of many of our experiments show that although this process is best viewed by magnetization studies, it is also reflected in magnetostriction, causes some changes in electronic transport and can be observed microscopically by NMR that proved electronic order alteration. All those facts suggest that the axis switching process observed and studied by us is intimately linked with the fast change of electronic trimeron order mentioned above.

  13. Magnetic field induced optical vortex beam rotation

    CERN Document Server

    Shi, Shuai; Zhou, Zhi-Yuan; Li, Yan; Zhang, Wei; Shi, Bao-Sen

    2015-01-01

    Light with orbital angular momentum (OAM) has drawn a great deal of attention for its important applications in the fields of precise optical measurements and high capacity optical communications. Here we adopt a method to study the rotation of a light beam, which is based on magnetic field induced circular birefringence in warm 87Rb atomic vapor. The dependence of the rotation angle to the intensity of the magnetic field makes it appropriate for weak magnetic field measurement. We derive a detail theoretical description that is in well agreement with the experimental observations. The experiment shows here provides a new method for precise measurement of magnetic field intensity and expands the application of OAM-carrying light.

  14. Stability, sub-gap current, 1/f-noise, and elemental depth profiling of annealed Al:Mn-AlOX-Al normal metal-insulator-superconducting tunnel junctions

    Science.gov (United States)

    Julin, J. K.; Chaudhuri, S.; Laitinen, M.; Sajavaara, T.; Maasilta, I. J.

    2016-12-01

    In this paper we report a study of the effect of vacuum annealing at 400°C on the properties of normal metal-insulator-superconductor (NIS) tunnel junctions, with manganese doped aluminium (Al:Mn) as the normal metal, aluminum as the superconductor and amorphous aluminum oxide as the tunneling barrier (Al:Mn-AlOx-Al). The annealing treatment improves the stability of the junctions, increases their tunneling resistance and does not have a negative impact on the low-temperature current-voltage characteristics. The measured 1/f resistance noise of the junctions also changes after annealing, in the best case decreasing by over an order of magnitude. All these observations show that annealing is a viable route to improve NIS junction devices after the sample has been fabricated.

  15. Direct-current and radio-frequency characterizations of GaAs metal-insulator-semiconductor field-effect transistors enabled by self-assembled nanodielectrics

    Science.gov (United States)

    Lin, H. C.; Kim, S. K.; Chang, D.; Xuan, Y.; Mohammadi, S.; Ye, P. D.; Lu, G.; Facchetti, A.; Marks, T. J.

    2007-08-01

    Direct-current and radio-frequency characterizations of GaAs metal-insulator-semiconductor field-effect transistors (MISFETs) with very thin self-assembled organic nanodielectrics (SANDs) are presented. The application of SAND on compound semiconductors offers unique opportunities for high-performance devices. Thus, 1μm gate-length depletion-mode n-channel SAND/GaAs MISFETs exhibit low gate leakage current densities of 10-2-10-5A/cm2, a maximum drain current of 260mA/mm at 2V forward gate bias, and a maximum intrinsic transconductance of 127mS/mm. These devices achieve a current cutoff frequency (fT) of 10.6GHz and a maximum oscillation frequency (fmax) of 6.9GHz. Nearly hysteresis-free Ids-Vgs characteristics and low flicker noise indicate that a high-quality SAND-GaAs interface is achieved.

  16. Low leakage Ru-strontium titanate-Ru metal-insulator-metal capacitors for sub-20 nm technology node in dynamic random access memory

    Energy Technology Data Exchange (ETDEWEB)

    Popovici, M., E-mail: Mihaela.Ioana.Popovici@imec.be; Swerts, J.; Redolfi, A.; Kaczer, B.; Aoulaiche, M.; Radu, I.; Clima, S.; Everaert, J.-L.; Van Elshocht, S.; Jurczak, M. [Imec, Leuven 3001 (Belgium)

    2014-02-24

    Improved metal-insulator-metal capacitor (MIMCAP) stacks with strontium titanate (STO) as dielectric sandwiched between Ru as top and bottom electrode are shown. The Ru/STO/Ru stack demonstrates clearly its potential to reach sub-20 nm technology nodes for dynamic random access memory. Downscaling of the equivalent oxide thickness, leakage current density (J{sub g}) of the MIMCAPs, and physical thickness of the STO have been realized by control of the Sr/Ti ratio and grain size using a heterogeneous TiO{sub 2}/STO based nanolaminate stack deposition and a two-step crystallization anneal. Replacement of TiN with Ru as both top and bottom electrodes reduces the amount of electrically active defects and is essential to achieve a low leakage current in the MIM capacitor.

  17. Reproducible bipolar resistive switching in entire nitride AlN/n-GaN metal-insulator-semiconductor device and its mechanism

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Yiren; Song, Hang, E-mail: songh@ciomp.ac.cn, E-mail: lidb@ciomp.ac.cn; Jiang, Hong; Li, Zhiming; Zhang, Zhiwei; Sun, Xiaojuan; Li, Dabing, E-mail: songh@ciomp.ac.cn, E-mail: lidb@ciomp.ac.cn; Miao, Guoqing [State Key Laboratory of Luminescence and Applications, Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, Changchun 130033 (China)

    2014-11-10

    Reproducible bipolar resistive switching characteristics are demonstrated in entire nitride AlN/n-GaN metal-insulator-semiconductor devices. The mechanism involved confirms to trap-controlled space charge limited current theory and can be attributed to the nitrogen vacancies of AlN serving as electron traps that form/rupture electron transport channel by trapping/detrapping electrons. This study will lead to the development of in-situ growth of group-III nitrides by metal-organic chemical vapor deposition as a candidate for next-generation nonvolatile memory device. Moreover, it will be benefit to structure monolithic integrated one-transistor-one-resistor memory with nitride high electron mobility transistors.

  18. Improved linearity in AlGaN/GaN metal-insulator-semiconductor high electron mobility transistors with nonlinear polarization dielectric

    Energy Technology Data Exchange (ETDEWEB)

    Gao, Tao [Fundamental Science on EHF Laboratory, University of Electronic Science and Technology of China (UESTC), Chengdu 611731 (China); Science and Technology on Monolithic Integrated Circuits and Modules Laboratory, Nanjing Electronic Devices Institute, Nanjing 210016 (China); Xu, Ruimin [Fundamental Science on EHF Laboratory, University of Electronic Science and Technology of China (UESTC), Chengdu 611731 (China); Kong, Yuechan, E-mail: kycfly@163.com; Zhou, Jianjun; Kong, Cen; Dong, Xun; Chen, Tangsheng [Science and Technology on Monolithic Integrated Circuits and Modules Laboratory, Nanjing Electronic Devices Institute, Nanjing 210016 (China)

    2015-06-15

    We demonstrate highly improved linearity in a nonlinear ferroelectric of Pb(Zr{sub 0.52}Ti{sub 0.48})-gated AlGaN/GaN metal-insulator-semiconductor high electron mobility transistor (MIS-HEMT). Distinct double-hump feature in the transconductance-gate voltage (g{sub m}-V{sub g}) curve is observed, yielding remarkable enhancement in gate voltage swing as compared to MIS-HEMT with conventional linear gate dielectric. By incorporating the ferroelectric polarization into a self-consistent calculation, it is disclosed that in addition to the common hump corresponding to the onset of electron accumulation, the second hump at high current level is originated from the nonlinear polar nature of ferroelectric, which enhances the gate capacitance by increasing equivalent dielectric constant nonlinearly. This work paves a way for design of high linearity GaN MIS-HEMT by exploiting the nonlinear properties of dielectric.

  19. High Electron Mobility Ge n-Channel Metal-Insulator-Semiconductor Field-Effect Transistors Fabricated by the Gate-Last Process with the Solid Source Diffusion Technique

    Science.gov (United States)

    Maeda, Tatsuro; Morita, Yukinori; Takagi, Shinichi

    2010-06-01

    We fabricate high-k/Ge n-channel metal-insulator-semiconductor field-effect transistors (MISFETs) by the gate-last process with the thermal solid source diffusion to achieve both of high quality source/drain (S/D) and gate stack. The n+/p junction formed by solid source diffusion technique of Sb dopant shows the excellent diode characteristics of ˜1.5×105 on/off ratio between +1 and -1 V and the quite low reverse current density of ˜4.1×10-4 A/cm2 at +1 V after the fabrication of high-k/Ge n-channel MISFETs that enable us to observe well-behaved transistor performances. The extracted electron mobility with the peak of 891 cm2/(V.s) is high enough to be superior to the Si universal electron mobility especially in low Eeff.

  20. Temperature dependent electrical characterisation of Pt/HfO{sub 2}/n-GaN metal-insulator-semiconductor (MIS) Schottky diodes

    Energy Technology Data Exchange (ETDEWEB)

    Shetty, Arjun, E-mail: arjun@ece.iisc.ernet.in; Vinoy, K. J. [Electrical Communication Engineering, Indian Institute of Science, Bangalore, India 560012 (India); Roul, Basanta; Mukundan, Shruti; Mohan, Lokesh; Chandan, Greeshma; Krupanidhi, S. B. [Materials Research Centre, Indian Institute of Science, Bangalore, India 560012 (India)

    2015-09-15

    This paper reports an improvement in Pt/n-GaN metal-semiconductor (MS) Schottky diode characteristics by the introduction of a layer of HfO{sub 2} (5 nm) between the metal and semiconductor interface. The resulting Pt/HfO{sub 2}/n-GaN metal-insulator-semiconductor (MIS) Schottky diode showed an increase in rectification ratio from 35.9 to 98.9(@ 2V), increase in barrier height (0.52 eV to 0.63eV) and a reduction in ideality factor (2.1 to 1.3) as compared to the MS Schottky. Epitaxial n-type GaN films of thickness 300nm were grown using plasma assisted molecular beam epitaxy (PAMBE). The crystalline and optical qualities of the films were confirmed using high resolution X-ray diffraction and photoluminescence measurements. Metal-semiconductor (Pt/n-GaN) and metal-insulator-semiconductor (Pt/HfO{sub 2}/n-GaN) Schottky diodes were fabricated. To gain further understanding of the Pt/HfO{sub 2}/GaN interface, I-V characterisation was carried out on the MIS Schottky diode over a temperature range of 150 K to 370 K. The barrier height was found to increase (0.3 eV to 0.79 eV) and the ideality factor decreased (3.6 to 1.2) with increase in temperature from 150 K to 370 K. This temperature dependence was attributed to the inhomogeneous nature of the contact and the explanation was validated by fitting the experimental data into a Gaussian distribution of barrier heights.

  1. Preparation and characterization of TaAlO{sub x} high-{kappa} dielectric for metal-insulator-metal capacitor applications

    Energy Technology Data Exchange (ETDEWEB)

    Hota, M.K., E-mail: mksan21@gmail.co [Dept of Electronics and ECE, Indian Institute of Technology, Kharagpur 721302 (India); Mahata, C. [Dept of Electronics and ECE, Indian Institute of Technology, Kharagpur 721302 (India); Bera, M.K. [Frontier Research Center, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503 (Japan); Mallik, S. [Dept of Electronics and ECE, Indian Institute of Technology, Kharagpur 721302 (India); Sarkar, C.K. [Dept of Electronics and Telecommunication Engineering, Jadavpur University, Jadavpur, Kolkata 700032 (India); Varma, S. [Institute of Physics, Bhubaneswar 751005 (India); Maiti, C.K. [Dept of Electronics and ECE, Indian Institute of Technology, Kharagpur 721302 (India)

    2010-10-29

    Metal-insulator-metal (MIM) capacitors with excellent electrical properties have been fabricated using high-{kappa} TaAlO{sub x}-based dielectrics. TaAlO{sub x} films having thickness of 11.5-26.0 nm, with equivalent oxide thickness (EOT) of {approx} 2.3-5.3 nm were deposited on top of Au/SiO{sub 2} (180 nm)/Si (100) structures by radio frequency magnetron co-sputtering of Ta{sub 2}O{sub 5} and Al{sub 2}O{sub 3} targets. The surface chemical states of the as-deposited TaAlO{sub x} films were characterized by high-resolution X-ray photoelectron spectroscopy. The crystallinity of the TaAlO{sub x} films for various post-deposition annealing treatments was characterized by grazing incident X-ray diffraction, which reveals that an amorphous phase is still retained for rapid thermal annealing up to 500 {sup o}C. Besides a high capacitance density ({approx} 5.4 to 6.6 fF/{mu}m{sup 2} at 1 kHz), a low value of voltage coefficients of capacitance and a stable temperature coefficient of capacitance have also been obtained in MIM capacitors with TaAlO{sub x} films. Degradation phenomenon of TaAlO{sub x}-based MIM capacitors under constant current stressing at 20 nA is found to be strongly dependent on dielectric thickness. It is shown that Al-incorporated Ta{sub 2}O{sub 5} (TaAlO{sub x}) films with high band gap and good thermal stability, low leakage current and good voltage linearity make it one of the most promising candidates for metal-insulator-metal capacitor applications.

  2. Exploratory Phase Transition-Based Switches Using Functional Oxides

    Science.gov (United States)

    2011-02-02

    structure was tested and the accuracy of Φ was estimated as ~ 0.02 eV.13 30 nm-thick Au/Cr layer including windows of 2 × 0.2 mm2 was coated on VO2 films...1039. (2) Mott, N. F. Metal-Insulator Transition. Reviews of Modern Physics 1968, 40, 677. (3) Goodenough , J. B. The two components of the

  3. Electric field-induced acoustic emission phenomena in ferroelectric and related ceramics

    Science.gov (United States)

    Aburatani, Hideaki

    Field induced AE phenomena in bulk ferroelectric and related ceramics as well as multilayer ceramic actuators were investigated in this work. Concerning the field induced AE measurement technique, it was shown that commonly used voltage application units can excite sample vibrations electromechanically through their voltage stabilization processes and generate extrinsic AE signals. In order to detect intrinsic AE signals from within piezoelectric samples, a modified voltage application unit with a long time constant tau was proposed. For the study of origins of field induced AE, a ferroelectric lead zirconate titanate (PZT-5A), an electrostrictive lead magnesium niobate-lead titanate (0.9PMN-0.1PT) and a field-enhanced ferroelectric type lead lanthanum zirconate titanate (PLZT(9/65/35)) ceramics were selected. Pre-applied maximum field dependence on the AE generation were observed for ferroelectric PZT-5A and electrostrictive 0.9PMN-0.1PT ceramics. The study showed that there are two origins for the field induced AE of the ferroelectric PZT-5A: deformation related to domain reorientation processes and piezoelectric deformation unrelated to domain reorientation processes. The stress induction/relaxation process simply caused by the electrostrictive deformation was found to be the origin of AE in the electrostrictive 0.9PMN-0.1PT ceramics. The electric field induced non-ferroelectric to ferroelectric transition, reorientation process of the induced ferroelectric domains and induced internal stress were found to be the origins of AE in the field-enhanced ferroelectric PLZT (9/65/35). The potential use of the AE method in production was explored using a Multilayer Ceramic Actuator (MCA) fabricated by a tape casting method.

  4. Universal Field-Induced Charge-Density-Wave Phase Diagram: Theory versus Experiment

    Science.gov (United States)

    Lebed, A. G.

    2009-07-01

    We suggest a theory of field-induced charge-density-wave phases, generated by high magnetic fields in quasi-low-dimensional conductors. We demonstrate that, in layered quasi-one-dimensional conductors, the corresponding critical magnetic field ratios are universal and do not depend on any fitting parameter. In particular, we find that H1/H0=0.73, H2/H0=0.59, H3/H0=0.49, and H4/H0=0.42, where Hn is a critical field of a phase transition between the field-induced charge-density-wave phases with numbers n and n+1. The suggested theory is in very good qualitative and quantitative agreement with the existing experimental data in α-(ET)2KHg(SCN)4 material.

  5. Field-induced magnetic states in holmium tetraboride

    Science.gov (United States)

    Brunt, D.; Balakrishnan, G.; Wildes, A. R.; Ouladdiaf, B.; Qureshi, N.; Petrenko, O. A.

    2017-01-01

    A study of the zero field and field induced magnetic states of the frustrated rare earth tetraboride HoB4 has been carried out using single crystal neutron diffraction complemented by magnetization measurements. In zero field, HoB4 shows magnetic phase transitions at TN 1=7.1 K to an incommensurate state with a propagation vector (δ ,δ ,δ') , where δ =0.02 and δ'=0.43 and at TN 2=5.7 K to a noncollinear commensurate antiferromagnetic structure. Polarized neutron diffraction measurements in zero field have revealed that the incommensurate reflections, albeit much reduced in intensity, persist down to 1.5 K despite antiferromagnetic ordering at 5.7 K. At lower temperatures, application of a magnetic field along the c axis initially re-establishes the incommensurate phase as the dominant magnetic state in a narrow field range, just prior to HoB4 ordering with an up-up-down ferrimagnetic structure characterized by the (h k 1/3 ) -type reflections between 18 and 24 kOe. This field range is marked by the previously reported M /Msat=1/3 magnetization plateau, which we also see in our magnetization measurements. The region between 21 and 33 kOe is characterized by the increase in the intensity of the antiferromagnetic reflections, such as (100), the maximum of which coincides with the appearance of the narrow magnetization plateau with M /Msat≈3/5 . Further increase of the magnetic field results in the stabilization of a polarized state above 33 kOe, while the incommensurate reflections are clearly present in all fields up to 59 kOe. We propose the H -T phase diagram of HoB4 for the H ∥c containing both stationary and transitionary magnetic phases which overlap and show significant history dependence.

  6. Giant electric-field-induced strain in lead-free piezoelectric materials.

    Science.gov (United States)

    Chen, Lan; Yang, Yurong; Meng, X K

    2016-05-03

    First-principles calculations are performed to investigate the structures, electrical, and magnetic properties of compressive BiFeO3 films under electric-field and pressure perpendicular to the films. A reversible electric-field-induced strain up 10% is achieved in the compressive BiFeO3 films. The giant strain originates from rhombohedral-tetragonal (R-T) phase transition under electric-filed, and is recoverable from tetragonal-rhombohedral (T-R) phase transition by compressive stress. Additionally, the weak ferromagnetism in BiFeO3 films is largely changed in R-T phase transition under electric-filed and T-R phase transition under pressure - reminiscent of magnetoelectric effect and magnetoelastic effect. These results suggest exciting device opportunities arising from the giant filed-induced strain, large magnetoelectric effect and magnetoelastic effect.

  7. Giant electric-field-induced strain in lead-free piezoelectric materials

    Science.gov (United States)

    Chen, Lan; Yang, Yurong; Meng, X. K.

    2016-01-01

    First-principles calculations are performed to investigate the structures, electrical, and magnetic properties of compressive BiFeO3 films under electric-field and pressure perpendicular to the films. A reversible electric-field-induced strain up 10% is achieved in the compressive BiFeO3 films. The giant strain originates from rhombohedral-tetragonal (R-T) phase transition under electric-filed, and is recoverable from tetragonal-rhombohedral (T-R) phase transition by compressive stress. Additionally, the weak ferromagnetism in BiFeO3 films is largely changed in R-T phase transition under electric-filed and T-R phase transition under pressure – reminiscent of magnetoelectric effect and magnetoelastic effect. These results suggest exciting device opportunities arising from the giant filed-induced strain, large magnetoelectric effect and magnetoelastic effect. PMID:27139526

  8. Si:SrTiO3-Al2O3-Si:SrTiO3 multi-dielectric architecture for metal-insulator-metal capacitor applications

    Science.gov (United States)

    Dugu, Sita; Pavunny, Shojan P.; Scott, James F.; Katiyar, Ram S.

    2016-11-01

    Metal-insulator-metal (MIM) capacitors comprised of amorphous Si:SrTiO3-Al2O3-Si:SrTiO3 multi-dielectric architecture have been fabricated employing a combination of pulsed laser and atomic layer deposition techniques. The voltage linearity, temperature coefficients of capacitance, dielectric and electrical properties upon thickness were studied under a wide range of temperature (200-400 K) and electric field stress (±1.5 MV/cm). A high capacitance density of 31 fF/μm2, a low voltage coefficient of capacitance of 363 ppm/V2, a low temperature coefficient of capacitance of <644 ppm/K, and an effective dielectric constant of ˜133 are demonstrated in a MIM capacitor with ˜1.4 nm capacitance equivalent thickness in a ˜40 nm thick ultra high-k multi-dielectric stack. All of these properties make this dielectric architecture of interest for next generation, highly scaled MIM capacitor applications.

  9. Low-frequency noise in AlTiO/AlGaN/GaN metal-insulator-semiconductor heterojunction field-effect transistors

    Science.gov (United States)

    Le, Son Phuong; Ui, Toshimasa; Nguyen, Tuan Quy; Shih, Hong-An; Suzuki, Toshi-kazu

    2016-05-01

    Using aluminum titanium oxide (AlTiO, an alloy of Al2O3 and TiO2) as a high-k gate insulator, we fabricated and investigated AlTiO/AlGaN/GaN metal-insulator-semiconductor heterojunction field-effect transistors. From current low-frequency noise (LFN) characterization, we find Lorentzian spectra near the threshold voltage, in addition to 1/f spectra for the well-above-threshold regime. The Lorentzian spectra are attributed to electron trapping/detrapping with two specific time constants, ˜25 ms and ˜3 ms, which are independent of the gate length and the gate voltage, corresponding to two trap level depths of 0.5-0.7 eV with a 0.06 eV difference in the AlTiO insulator. In addition, gate leakage currents are analyzed and attributed to the Poole-Frenkel mechanism due to traps in the AlTiO insulator, where the extracted trap level depth is consistent with the Lorentzian LFN.

  10. Investigation of passivation effects in AlGaN/GaN metal-insulator-semiconductor high electron-mobility transistor by gate-drain conductance dispersion study

    Institute of Scientific and Technical Information of China (English)

    Bi Zhi-Wei; Chang Yong-Ming; Li Zhi-Ming; Mei Nan; Hu Zhen-Hua; Mao Wei; Hao Yue; Feng Qian; Cao Yan-Rong; Gao Zhi-Yuan; Zhang Jin-Cheng; Ma Xiao-Hua

    2011-01-01

    This paper studies the drain current collapse of AlGaN/GaN metal-insulator-semiconductor high electron-mobility transistors(MIS-HEMTs)with NbAlO dielectric by applying dual-pulsed stress to the gate and drain of the device.For NbAlO MIS-HEMT,smaller current collapse is found,especially when the gate static voltage is-8 V.Through a thorough study of the gate-drain conductance dispersion,it is found that the growth of NbAlO can reduce the trap density of the AlGaN surface.Therefore,fewer traps can be filled by gate electrons,and hence the depletion effect in the channel is suppressed effectively.It is proved that the NbAlO gate dielectric can not only decrease gate leakage current but also passivate the AlGaN surface effectively,and weaken the current collapse effect accordingly.

  11. Investigation of a 4H-SiC metal-insulation-semiconductor structure with an Al2O3/SiO2 stacked dielectric

    Institute of Scientific and Technical Information of China (English)

    Tang Xiao-Yan; Song Qing-Wen; Zhang Yu-Ming; Zhang Yi-Men; Jia Ren-Xu; Lü Hong-Liang; Wang Yue-Hu

    2012-01-01

    Atomic layer deposited (ALD) Al2O3/dry-oxidized ultrathin SiO2 films as a high-k gate dielectric grown on 8° off-axis 4H-SiC (0001) epitaxial wafers are investigated in this paper.The metal-insulation-semiconductor (MIS) capacitors,respectively with different gate dielectric stacks (Al2O3/SiO2,Al2O3,and SiO2) are fabricated and compared with each other.The I-V measurements show that the Al2O3/SiO2 stack has a high breakdown field (≥12 MV/cm)comparable to SiO2,and a relatively low gate leakage current of 1 × 10-7 A/cm2 at an electric field of 4 MV/cm comparable to Al2O3.The 1-MHz high frequency C-V measurements exhibit that the Al2O3/SiO2 stack has a smaller positive flat-band voltage shift and hysteresis voltage,indicating a less effective charge and slow-trap density near the interface.

  12. Atomic-layer-deposited Al{sub 2}O{sub 3}-HfO{sub 2} laminated and sandwiched dielectrics for metal-insulator-metal capacitors

    Energy Technology Data Exchange (ETDEWEB)

    Ding Shijin; Zhang, D W; Wang, Likang [State Key Laboratory of ASIC and System, School of Microelectronics, Fudan University, Shanghai 200433 (China)

    2007-02-21

    Metal-insulator-metal (MIM) capacitors with atomic-layer-deposited Al{sub 2}O{sub 3}-HfO{sub 2} laminated and sandwiched dielectrics have been fabricated and electrically compared for analog circuit applications. The experimental results indicate that the laminated dielectrics exhibit much better leakage and breakdown characteristics than the sandwiched ones while maintaining higher capacitance densities and acceptable voltage linearity. In respect of the 1 nm Al{sub 2}O{sub 3} and 10 nm HfO{sub 2} laminated dielectric, the resulting capacitor offers an extremely low leakage current of 2.4 x 10{sup -9} A cm{sup -2} at 8 V and a breakdown electric field of {approx}3.3 MV cm{sup -1} at 125 deg. C together with a capacitance density of {approx}3.1 fF {mu}m{sup -2} and voltage coefficients of capacitance of 100 ppm V{sup -2} and -80 ppm V{sup -1} at 100 kHz. The superiority of the laminated dielectrics correlates with inhibition of HfO{sub 2} crystallization, discontinuity of the grain boundary channels from the top to the bottom and changes of the dielectric electronic properties due to the bonding and polarization effects at the multi-interfaces.

  13. Experimental and modeling study of the capacitance-voltage characteristics of metal-insulator-semiconductor capacitor based on pentacene/parylene

    KAUST Repository

    Wondmagegn, Wudyalew T.

    2011-04-01

    The capacitance-voltage (C-V) characteristics of metal-insulator- semiconductor (MIS) capacitors consisting of pentacene as an organic semiconductor and parylene as the dielectric have been investigated by experimental, analytical, and numerical analysis. The device simulation was performed using two-dimensional drift-diffusion methods taking into account the Poole-Frenkel field-dependent mobility. Pentacene bulk defect states and fixed charge density at the semiconductor/insulator interface were incorporated into the simulation. The analysis examined pentacene/parylene interface characteristics for various parylene thicknesses. For each thickness, the corresponding flat band voltage extracted from the C-V plot of the MIS structure was more negative than - 2.4 V. From the flat band voltage the existence of a significant mismatch between the work functions of the gate electrode and pentacene active material has been identified. Experimental and simulation results suggest the existence of interface charge density on the order of 3 × 1011 q/cm2 at the insulator/semiconductor interface. The frequency dispersion characteristics of the device are also presented and discussed. © 2011 Elsevier B.V.

  14. Numerical studies on a plasmonic temperature nanosensor based on a metal-insulator-metal ring resonator structure for optical integrated circuit applications

    Science.gov (United States)

    Al-mahmod, Md. Jubayer; Hyder, Rakib; Islam, Md Zahurul

    2017-07-01

    A nanosensor, based on a metal-insulator-metal (MIM) plasmonic ring resonator, is proposed for potential on-chip temperature sensing and its performance is evaluated numerically. The sensor components can be fabricated by using planar processes on a silicon substrate, making its manufacturing compatible to planar electronic fabrication technology. The sensor, constructed using silver as the metal rings and a thermo-optic liquid ethanol film between the metal layers, is capable of sensing temperature with outstanding optical sensitivity, as high as -0.53 nm/°C. The resonance wavelength is found to be highly sensitive to the refractive index of the liquid dielectric film. The resonance peak can be tuned according to the requirement of intended application by changing the radii of the ring resonator geometries in the design phase. The compact size, planar and silicon-based design, and very high resolutions- these characteristics are expected to make this sensor technology a preferred choice for lab-on-a-chip applications, as compared to other contemporary sensors.

  15. Influence of neighboring coupling on metal-insulator-semiconductor (MIS) deep-depletion tunneling current via Schottky barrier height modulation mechanism

    Science.gov (United States)

    Yang, Ming-Han; Hwu, Jenn-Gwo

    2017-04-01

    A metal-insulator-semiconductor (MIS) tunneling diode is a very promising sensor due to its deep depletion phenomenon. The coupling effect between two adjacent devices is therefore of importance. To study the MIS deep-depletion tunneling current coupling phenomenon, a device pattern of one centric circle coupled with one or two surrounding rings was devised. It was found that MIS(p) tunneling current with the Schottky barrier height modulation mechanism is enhanced just by locating more MIS(p) structures nearby or by shortening their relative distance, which can again be verified under light exposure. The MIS(n) structure was also fabricated for comparison. It was observed in MIS(n) that, with the lack of the Schottky barrier height modulation mechanism, tunneling current is greater and almost immune to light irradiance compared to MIS(p). Besides, the edge oxide of MIS(p) is removed to change its Schottky barrier height modulation capability. Significantly lower deep-depletion tunneling current and invulnerability to the adjacent minority condition were observed. Surprisingly, it offers smaller saturation voltage and better photosensitivity.

  16. Effective surface treatment for GaN metal-insulator-semiconductor high-electron-mobility transistors using HF plus N2 plasma prior to SiN passivation

    Science.gov (United States)

    Liu, Shih-Chien; Trinh, Hai-Dang; Dai, Gu-Ming; Huang, Chung-Kai; Dee, Chang-Fu; Yeop Majlis, Burhanuddin; Biswas, Dhrubes; Chang, Edward Yi

    2016-01-01

    An effective surface cleaning technique is demonstrated for the GaN metal-insulator-semiconductor high-electron-mobility transistor (MIS-HEMT) passivation process. In this study, dilute HF solution and in situ N2 plasma treatments were adopted to remove the native oxide and recover the nitrogen-vacancy defects at the GaN surface before device passivation. To investigate the correlation between the properties of the SiN/GaN interface and the device performance, the GaN MIS-HEMTs were characterized using current-voltage (I-V) measurement, capacitance-voltage (C-V) measurement, and X-ray photoelectron spectroscopy (XPS) analysis. With the application of this surface treatment technique, the device exhibits improved I-V characteristics with low leakage current, low dynamic ON-resistance, and good C-V response with a steep slope. Overall, the results reveal that the oxide-related bonds and nitrogen-vacancy defects at the SiN/GaN interface are the root cause of the GaN MIS-HEMTs performance degradation.

  17. AlGaN/GaN metal-insulator-semiconductor high electron mobility transistors with reduced leakage current and enhanced breakdown voltage using aluminum ion implantation

    Energy Technology Data Exchange (ETDEWEB)

    Sun, Shichuang [Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Wuhan 430074 (China); Key Laboratory of Nanodevices and Applications, Suzhou Institute of Nano-Tech and Nano-Bionics, CAS, Suzhou 215123 (China); Fu, Kai, E-mail: kfu2009@sinano.ac.cn, E-mail: cqchen@mail.hust.edu.cn; Yu, Guohao; Zhang, Zhili; Song, Liang; Deng, Xuguang; Li, Shuiming; Sun, Qian; Cai, Yong; Zhang, Baoshun [Key Laboratory of Nanodevices and Applications, Suzhou Institute of Nano-Tech and Nano-Bionics, CAS, Suzhou 215123 (China); Qi, Zhiqiang; Dai, Jiangnan; Chen, Changqing, E-mail: kfu2009@sinano.ac.cn, E-mail: cqchen@mail.hust.edu.cn [Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Wuhan 430074 (China)

    2016-01-04

    This letter has studied the performance of AlGaN/GaN metal-insulator-semiconductor high electron mobility transistors on silicon substrate with GaN buffer treated by aluminum ion implantation for insulating followed by a channel regrown by metal–organic chemical vapor deposition. For samples with Al ion implantation of multiple energies of 140 keV (dose: 1.4 × 10{sup 14} cm{sup −2}) and 90 keV (dose: 1 × 10{sup 14} cm{sup −2}), the OFF-state leakage current is decreased by more than 3 orders and the breakdown voltage is enhanced by nearly 6 times compared to the samples without Al ion implantation. Besides, little degradation of electrical properties of the 2D electron gas channel is observed where the maximum drain current I{sub DSmax} at a gate voltage of 3 V was 701 mA/mm and the maximum transconductance g{sub mmax} was 83 mS/mm.

  18. Effective Contact Potential of Thin Film Metal-Insulator Nanostructures and Its Role in Self-Powered Nanofilm X-ray Sensors.

    Science.gov (United States)

    Brivio, Davide; Ada, Earl; Sajo, Erno; Zygmanski, Piotr

    2017-03-29

    We studied the effective contact potential difference (ECPD) of thin film nanostructures and its role in self-powered X-ray sensors, which use the high-energy current detection scheme. We compared the response to kilovoltage X-rays of several nanostructures made of disparate combinations of conductors (Al, Cu, Ta, ITO) and oxides (SiO2, Ta2O5, Al2O3). We measured current-voltage curves in parallel-plate configuration separated by an air gap and determined three characteristic parameters: current at zero voltage bias I0, the voltage offset for zero current ECPD, and saturation current Isat. We found that the metals' ECPD values measured with our technique were higher than the CPD values measured with photoelectron spectroscopy in situ, i.e., no air contact. These differences are related to natural oxidization and to the presence of photo-/Auger-electron current leaking from the high-Z toward the low-Z electrode, as suggested by additional experiments carried out in vacuum. Further, the deposition of the 40-500 nm oxide layer on the surface of metallic substrates strongly affects their contact potential. This technique exploits ionization and charge carrier transport in both solid insulators and in air, and it opens the possibility of measuring the ECPD between metals separated by a solid insulator in a metal-insulator-metal (MIM) configuration. Additionally, we demonstrated that certain configurations of MIM structures are suitable for X-ray detection in self-powered mode.

  19. Characterization of Al2O3/GaN/AlGaN/GaN metal-insulator-semiconductor high electron mobility transistors with different gate recess depths

    Institute of Scientific and Technical Information of China (English)

    Ma Xiao-Hua; Pan Cai-Yuan; Yang Li-Yuan; Yu Hui-You; Yang Ling; Quan Si; Wang Hao; Zhang Jin-Cheng; Hao Yue

    2011-01-01

    In this paper, in order to solve the interface-trap issue and enhance the transconductance induced by high-k dielectric in metal-insulator-semiconductor (MIS) high electron mobility transistors (HEMTs), we demonstrate better performances of recessed-gate Al2O3 MIS-HEMTs which are fabricated by Fluorine-based Si3N4 etching and chlorinebased AlGaN etching with three etching times (15 s, 17 s and 19 s). The gate leakage current of MIS-HEMT is about three orders of magnitude lower than that of AlGaN/GaN HEMT. Through the recessed-gate etching, the transconductance increases effectively. When the recessed-gate depth is 1.02 nm, the best interface performance with γit=(0.20-1.59) μs and Dit=(0.55-1.08)×1012 cm-2·eV-1 can be obtained. After chlorine-based etching, the interface trap density reduces considerably without generating any new type of trap. The accumulated chlorine ions and the N vacancies in the AlGaN surface caused by the plasma etching can degrade the breakdown and the high frequency performances of devices. By comparing the characteristics of recessed-gate MIS-HEMTs with different etching times, it is found that a low power chlorine-based plasma etching for a short time (15 s in this paper) can enhance the performances of MIS-HEMTs effectively.

  20. Design of periodic metal-insulator-metal waveguide back structures for the enhancement of light absorption in thin-film solar cells

    Institute of Scientific and Technical Information of China (English)

    Zheng Gai-Ge; Jiang Jian-Li; Xian Feng-Lin; Qiang Hai-Xia; Wu Hong; Li Xiang-Yin

    2011-01-01

    To increase the absorption in a thin layer of absorbing material (amorphous silicon,arSi),a light trapping design is presented. The designed structure incorporates periodic metal-insulator-metal waveguides to enhance the optical path length of light within the solar cells. The new design can result in broadband optical absorption enhancement not only for transverse magnetic (TM)-polarized light,but also for transverse electric (TE)-polarized light. No plasmonic modes can be excited in TE-polarization,but because of the coupling into the a.Si planar waveguide guiding modes and the diffraction of light by the bottom periodic structures into higher diffraction orders,the total absorption in the active region is also increased. The results from rigorous coupled wave analysis show that the overall optical absorption in the active layer can be greatly enhanced by up to 40%. The designed structures presented in this paper can be integrated with back contact technology to potentially produce high-efficiency thin-film solar cell devices.

  1. Electrical Conduction Mechanisms in Metal-Insulator-Metal (MIM) Structure with TiO x N y Thin Films Deposited with Different O/N Ratios

    Science.gov (United States)

    Libardi, Juliano; Grigorov, Korneli G.; Moraes, Rodrigo S.; Guerino, Marciel; Da Silva Sobrinho, Argemiro S.; Massi, Marcos

    2015-01-01

    In this work, the current-voltage characteristics of titanium oxynitride thin films were measured and the charge carrier transport mechanisms established as a function of film composition. The films were deposited by magnetron sputtering, where the oxygen/nitrogen ratio was varied via a pulsing technique to enable the achievement of desired concentrations. Thus, the obtained films showed metallic titanium nitrate (TiN) or semiconductor titanium dioxide (TiO2) character and were used to fabricate metal-insulator-metal structures. An ohmic conduction mechanism was identified in the films with higher nitrogen incorporation or presenting TiN-rich phase. Decrease in the nitrogen content resulted in films with TiO2-rich phase. In this case, Poole-Frenkel and space-charge-limited current conduction mechanisms were observed. The dielectric constants were calculated from the high-frequency capacitance-voltage dependences, with a reduction from 10 to 3 being observed due to the stoichiometric changes and probable incorporation of defects into the film structure. Finally, the film composition and structural characteristics of the films were revealed by Rutherford backscattering and x-ray diffraction techniques, respectively.

  2. High density Al2O3/TaN-based metal-insulator metal capacitors in application to radio frequency integrated circuits

    Institute of Scientific and Technical Information of China (English)

    Ding Shi-Jin; Huang Yu-Jian; Huang Yue; Pan Shao-Hui; Zhang Wei; Wang Li-Kang

    2007-01-01

    Metal-insulator-metal (MIM) capacitors with atomic-layer-deposited A12O3 dielectric and reactively sputtered TaN electrodes in application to radio frequency integrated circuits have been characterized electrically. The capacitors exhibit a high density of about 6.05 fF/μm2, a small leakage current of 4.8 × 10-8 A/cm2 at 3 V, a high breakdown electric field of 8.61 MV/cm as well as acceptable voltage coefficients of capacitance (VCCs) of 795 ppm/V2 and 268 ppm/V at 1 MHz. The observed properties should be attributed to high-quality Al2O3 film and chemically stable TaN electrodes.Further, a logarithmically linear relationship between quadratic VCC and frequency is observed due to the change of relaxation time with carrier mobility in the dielectric. The conduction mechanism in the high field ranges is dominated by the Poole-Frenkel emission, and the leakage current in the low field ranges is likely to be associated with trap-assisted tunnelling. Meanwhile, the Al2O3 dielectric presents charge trapping under low voltage stresses, and defect generation under high voltage stresses, and it has a hard-breakdown performance.

  3. Electrical Characterization of Metal-Insulator-Metal Capacitors with Atomic-Layer-Deposited HfO2 Dielectrics for Radio Frequency Integrated Circuit Application

    Institute of Scientific and Technical Information of China (English)

    HUANG Yu-Jian; HUANG Yue; DING Shi-Jin; ZHANG Wei; LIU Ran

    2007-01-01

    Metal-insulator-metal (MIM) capacitors with atomic-layer-deposited HfO2 dielectric and TaN electrodes are investigated for rf integrated circuit applications. For 12nm HfO2, the fabricated capacitor exhibits a high capacitance density of 15.5fF/μm2 at 100kHz, a small leakage current density of 6.4 × 10-9 A/cm2 at 1.8 V and 125℃, a breakdown electric field of 2.6 MV/cm as well as voltage coefficients of capacitance (VCCs) of 2110ppm/V2 and -824 ppm/V at 100kHz. Further, it is deduced that the conduction mechanism in the high field range is dominated by the Poole-Frenkel emission, and the conduction mechanism in the low field range is possibly related to trap-assisted tunnelling. Finally, comparison of various HfO2 MIM capacitors is present,suggesting that the present MIM capacitor is a promising candidate for future rf integrated circuit application.

  4. Initial Processes of Atomic Layer Deposition of Al2O3 on InGaAs: Interface Formation Mechanisms and Impact on Metal-Insulator-Semiconductor Device Performance

    Directory of Open Access Journals (Sweden)

    Shinichi Takagi

    2012-03-01

    Full Text Available Interface-formation processes in atomic layer deposition (ALD of Al2O3 on InGaAs surfaces were investigated using on-line Auger electron spectroscopy. Al2O3 ALD was carried out by repeating a cycle of Al(CH33 (trimethylaluminum, TMA adsorption and oxidation by H2O. The first two ALD cycles increased the Al KLL signal, whereas they did not increase the O KLL signal. Al2O3 bulk-film growth started from the third cycle. These observations indicated that the Al2O3/InGaAs interface was formed by reduction of the surface oxides with TMA. In order to investigate the effect of surface-oxide reduction on metal-insulator-semiconductor (MIS properties, capacitors and field-effect transistors (FETs were fabricated by changing the TMA dosage during the interface formation stage. The frequency dispersion of the capacitance-voltage characteristics was reduced by employing a high TMA dosage. The high TMA dosage, however, induced fixed negative charges at the MIS interface and degraded channel mobility.

  5. Resolving the VO2 controversy: Mott mechanism dominates the insulator-to-metal transition

    Science.gov (United States)

    Nájera, O.; Civelli, M.; Dobrosavljević, V.; Rozenberg, M. J.

    2017-01-01

    We consider a minimal model to investigate the metal-insulator transition in VO2. We adopt a Hubbard model with two orbitals per unit cell, which captures the competition between Mott and singlet-dimer localization. We solve the model within dynamical mean-field theory, characterizing in detail the metal-insulator transition and finding new features in the electronic states. We compare our results with available experimental data, obtaining good agreement in the relevant model parameter range. Crucially, we can account for puzzling optical conductivity data obtained within the hysteresis region, which we associate with a metallic state characterized by a split heavy quasiparticle band. Our results show that the thermal-driven insulator-to-metal transition in VO2 is compatible with a Mott electronic mechanism, providing fresh insight to a long-standing "chicken-and-egg" debate and calling for further research of "Mottronics" applications of this system.

  6. Metal-Insulator Transition in Ca-Doped Sr14-xCaxCu24O41 Systems Probed by Thermopower Measurements

    Institute of Scientific and Technical Information of China (English)

    WANG Qing-Bo; XU Xiang-Fan; TAO Qian; WANG Hong-Tao; XU Zhu-An

    2008-01-01

    High quality Sr14-x Cax Cu24 O41 single-crystals are successfully grown by fioating-zone technique,and the transport properties are studied.The temperature dependence of resistivity along the c-axis direction is semiconductorlike for x ≤ 10 and it can be fitted by the thermal activation equation ρ = ρ0 exp(Δ/kBT) with kB being the Boltzmann constant and Δ the activation energy.A break in the slope of thermopower (S) versus the inverse temperature (1/T) corresponding to the formation of charge-density waves (CDW) is first observed for x ≤ 6.The temperature dependence of thermopower becomes metallic for x ≥ 8 while the resistivity is still semiconductorlike.We propose that the insulation behaviour of the resistivity in the Ca doping range 8 ≤ x ≥ 11 could result from the localization of the charge carriers due to the disorder induced by Ca doping and a revised electronic phase diagram is derived based on our observations.

  7. Metal-insulator Transition in Complex Oxides%复杂氧化物中的金属-绝缘体转变

    Institute of Scientific and Technical Information of China (English)

    宋创业; 姚携菲; 张金星

    2015-01-01

    理解金属-绝缘体转变机制有助于进一步了解复杂氧化物中的微观物理行为.基于复杂氧化物材料,首先介绍金属-绝缘体的转变机制:Wilson转变、Mott转变、Anderson转变和Peierls转变.除上述四种机制外,以锰氧化物材料为例,阐述双交换机制和Jahn-Taller畸变的作用对铁磁自旋有序的影响,以及s-d杂化、掺杂和电子-声子散射所引起的铁磁金属到顺磁绝缘态的转变.同时介绍含有磁性粒子的非磁材料中的近藤效应,进而分析外界磁场作用对锰氧化物材料输运性质的影响.

  8. Metal-Insulator Transition in the Organic Metal \\(TTM-TTP\\)I3 with a One-Dimensional Half-Filled Band

    Science.gov (United States)

    Mori, T.; Kawamoto, T.; Yamaura, J.; Enoki, T.; Misaki, Y.; Yamabe, T.; Mori, H.; Tanaka, S.

    1997-09-01

    The title 1:1 composition organic conductor, with a highly one-dimensional half-filled energy band, exhibits metallic conductivity down to TMI~160 K, but the spin susceptibility follows the one-dimensional Heisenberg model from room temperature to 2 K, without any anomaly at TMI. The insulating state is regarded as a Mott insulator. The small U, related to the extended molecular structure, gives rise to the small charge gap and the high-temperature metallic conduction.

  9. Antiferromagnetic, metal-insulator, and superconducting phase transitions in underdoped cuprates: Slave-fermion t-J model in the hopping expansion

    Science.gov (United States)

    Shimizu, Akihiro; Aoki, Koji; Sakakibara, Kazuhiko; Ichinose, Ikuo; Matsui, Tetsuo

    2011-02-01

    We study a system of doped antiferromagnet in three dimensions at finite temperatures using the t-J model, a canonical model of strongly correlated electrons. We employ the slave-fermion representation of electrons, in which an electron is described as a composite of a charged spinless holon and a chargeless spinon. We introduce two kinds of U(1) gauge fields on links as auxiliary fields, one describing resonating valence bonds of antiferromagnetic nearest-neighbor spin pairs and the other for nearest-neighbor hopping amplitudes of holons and spinons in the ferromagnetic channel. To perform a numerical study of the system, we integrate out the fermionic holon field by using the hopping expansion in powers of the hopping amplitude, which is legitimate for the region in and near the insulating phase. The resultant effective model is described in terms of bosonic spinons, two U(1) gauge fields, and a collective field for hole pairs. We study this model by means of Monte Carlo simulations, calculating the specific heat, spin correlation functions, and instanton densities. We obtain a phase diagram in the hole concentration-temperature plane, which is in good agreement with that observed recently for clean and homogeneous underdoped samples.

  10. Metal-insulator transition at the LaAlO3/SrTiO3 interface revisited: A hybrid functional study

    KAUST Repository

    Cossu, Fabrizio

    2013-07-17

    We investigate the electronic properties of the LaAlO3/SrTiO3 interface using density functional theory. In contrast to previous studies, which relied on (semi-)local functionals and the GGA+U method, we here use a recently developed hybrid functional to determine the electronic structure. This approach offers the distinct advantage of accessing both the metallic and insulating multilayers on a parameter-free equal footing. As compared to calculations based on semilocal GGA functionals, our hybrid functional calculations lead to a considerably increased band gap for the insulating systems. The details of the electronic structure show substantial deviations from those obtained by GGA calculations. This casts severe doubts on all previous results based on semilocal functionals. In particular, corrections using rigid band shifts (“scissors operator”) cannot lead to valid results.

  11. Magnetism variations and susceptibility hysteresis at the metal-insulator phase transition temperature of VO2 in a composite film containing vanadium and tungsten oxides

    CSIR Research Space (South Africa)

    Akande, AA

    2015-02-01

    Full Text Available We report on the magnetic property of 0.67–WO3+0.33–VOx mixture film deposit on the corning glass substrate using the chemical sol–gel and atmospheric pressure chemical vapour deposition (APCVD) methods. The XRD and Raman spectroscopy confirm...

  12. Excitations and enhanced coupling at the magnetic metal-insulator transition in NaOsO3 and Cd2 Os2 O7

    Science.gov (United States)

    Calder, S.; Lee, J. H.; Stone, M. B.; Vale, J. G.; Donnerer, C.; Bogdanov, N. A.; Lang, J.; Feygenson, M.; Liu, X.; Upton, M. H.; Casa, D.; Lumsden, M. D.; Zhao, Z.; Yan, J.-Q.; Shi, Y. G.; Sun, Y. S.; Tsujimoto, Y.; Yamaura, K.; Mandrus, D.; Nishimoto, S.; Brink, J. Vd; Hill, J. P.; McMorrow, D. F.; Christianson, A. D.

    5d oxides provide new paradigms of cooperative interactions that drive novel emergent behavior. This is exemplified in the osmates NaOsO3 and Cd2Os2O7 that host MITs where magnetic order appears intimately entwined. However, unlike the iridates where spin-orbit coupling (SOC) behavior dominates, in the 5d3 osmates an orbital singlet is expected and reduced effect of SOC. We measure the inelastic spectra with neutrons and RIXS. Our results uncover the 5d-manifold splitting to reveal a suppressed role of SOC in the creation of the electronic ground state but dominant behavior in the creation of the magnetic state. Moreover at the MIT in NaOsO3 we find a giant spin-phonon coupling and in Cd2Os2O7 a magnetic excitation corresponding to a superposition of multiple spin-flips.

  13. Superconductivity and magnetic field induced spin density waves in the (TMTTF)2X family

    Science.gov (United States)

    Balicas, L.; Behnia, K.; Kang, W.; Canadell, E.; Auban-Senzier, P.; Jérome, D.; Ribault, M.; Fabre, J. M.

    1994-10-01

    We report magnetotransport measurements in the quasi one dimensional (Q-1-D) organic conductor (TMTTF)2Br at pressures up to 26 kbar, clown to 0.45 K in magnetic fields up to 19 T along the c^{ast} direction. It is found that a superconducting ground state is stabilized under 26 kbar at T_C = 0.8 K. No magnetic field induced spin density wave (FISDW) transitions are observed below 19T unlike other Q-1-D superconductors pertaining to the selenium series. The computed amplitude of the interchain coupling along transverse directions is unable to explain the missing; FISDW instability.

  14. The anisotropy of the surface tension at the magnetic-field-induced phase transformations

    CERN Document Server

    Cebers, A

    2002-01-01

    The surface properties of the magnetic colloid phases arising at the magnetic-field-induced phase separation in the Hele-Shaw cell are considered. By the numerical resolution of the equation for the concentration distribution in the transition layer between the phases, the anisotropy of the surface tension is calculated. The anisotropic shapes of the droplets of the concentrated phase are found by the Wulff construction and are compared with that obtained by the numerical simulation of the kinetics of the magnetic colloid phase separation in the Hele-Shaw cell.

  15. Field induced polarization and magnetization behaviour of Gd-doped lead magnesium niobate ceramics

    Science.gov (United States)

    Pandey, Adityanarayan; Gupta, Surya Mohan; Nigam, Arun Kumar

    2016-05-01

    Both superparaelectric and superparamagnetic behaviour has been observed in rare earth magnetic ion Gd3+ doped Lead Magnesium Niobate (Gd-PMN). Field induced polarization and magnetization studies reveal hystresis loss free P-E and M-H loop at 300K and 5K, respectively. Temperature dependence of inverse susceptibility plot shows deviation at a temperature "td" when fitted with the Curie-Weiss law. This deviation has been attributed to transition from paramagnetic to superparamagnetic behaviour as reported in amorphous Pd-Ni-Fe-P alloys.

  16. Theoretical and experimental study of the quasistatic capacitance of metal-insulator-hydrogenated amorphous silicon structures: Strong evidence for the defect-pool model

    Science.gov (United States)

    Kleider, J. P.; Dayoub, F.

    1998-10-01

    The density of localized states in hydrogenated amorphous silicon (a-Si:H) is studied by means of the quasistatic capacitance technique applied to metal-insulator a-Si:H structures. Calculations in the framework of the defect-pool model show that the changes in the quasistatic capacitance versus gate bias curves (qs-CV curves) after bias annealing reveal the changes in the density of dangling-bond states predicted by the model, and are sensitive to the defect-pool parameters. The comparison of theoretical qs-CV curves with experimental curves obtained in a wide range of bias-anneal voltages Vba on several kinds of structures (top gate oxide, top gate nitride, and the most commonly used bottom gate nitride structures) strongly support the defect-pool model, and values for the model parameters are deduced. It is shown that for all structures the dominant phenomenon for bias annealing at positive Vba (i.e., under electron accumulation) is the creation of defects in the lower part of the gap in the a-Si:H. Bias annealing under hole accumulation reveals the creation of defects in the upper part of the gap of a-Si:H, but the precise dependence of the qs-CV curves upon Vba depends on the nature of the insulator-a-Si:H interface. In particular, it is affected by a higher density of interface trap levels in the top gate nitride structures, and by hole injection and trapping from the a-Si:H into the nitride layer in the bottom gate nitride structures.

  17. Properties of atomic-vapor and atomic-layer deposited Sr, Ti, and Nb doped Ta{sub 2}O{sub 5} Metal-Insulator-Metal capacitors

    Energy Technology Data Exchange (ETDEWEB)

    Lukosius, M., E-mail: lukosius@ihp-microelectronics.com [IHP, Im Technologiepark 25, 15236 Frankfurt Oder (Germany); Kaynak, C. Baristiran; Kubotsch, S. [IHP, Im Technologiepark 25, 15236 Frankfurt Oder (Germany); Blomberg, T. [ASM Microchemistry Ltd., Vaeinoe Auerin katu 12 A, 00560 Helsinki (Finland); Ruhl, G. [Infineon Technologies AG, Wernerwerkstr. 2, 93049 Regensburg (Germany); Wenger, Ch. [IHP, Im Technologiepark 25, 15236 Frankfurt Oder (Germany)

    2012-05-01

    Atomic Vapor Deposition and Atomic Layer Deposition techniques were applied for the depositions of Ta{sub 2}O{sub 5}, Ti-Ta-O, Sr-Ta-O and Nb-Ta-O oxide films for Metal-Insulator-Metal (MIM) capacitors used in back-end of line for Radio Frequency applications. Structural and electrical properties were studied. Films, deposited on the TiN bottom electrodes, in the temperature range of 225-400 Degree-Sign C, were amorphous, whereas the post deposition annealing at 600 Degree-Sign C resulted in the crystallization of Nb-Ta-O films. Electrical properties of MIM structures, investigated after sputtering Au top electrodes, revealed that the main characteristics were different for each oxide. On one hand, Ti-Ta-O based MIM capacitors possessed the highest dielectric constant (50), but the leakages currents were also the highest ({approx} 10{sup -5} A/cm{sup 2} at - 2 V). On the other hand, Sr-Ta-O showed the lowest leakage current densities ({approx} 10{sup -9} A/cm{sup 2} at - 2 V) as well as the smallest capacitance-voltage nonlinearity coefficients (40 ppm/V{sup 2}), but the dielectric constant was the smallest (20). The highest nonlinearity coefficients (290 ppm/V{sup 2}) were observed for Nb-Ta-O based MIM capacitors, although relatively high dielectric constant (40) and low leakage currents ({approx} 10{sup -7} A/cm{sup 2} at - 2 V) were measured. Temperature dependent leakage-voltage measurements revealed that only Sr-Ta-O showed no dependence of leakage current as a function of the measurement temperature.

  18. Silicon dioxide with a silicon interfacial layer as an insulating gate for highly stable indium phosphide metal-insulator-semiconductor field effect transistors

    Science.gov (United States)

    Kapoor, V. J.; Shokrani, M.

    1991-01-01

    A novel gate insulator consisting of silicon dioxide (SiO2) with a thin silicon (Si) interfacial layer has been investigated for high-power microwave indium phosphide (InP) metal-insulator-semiconductor field effect transistors (MISFETs). The role of the silicon interfacial layer on the chemical nature of the SiO2/Si/InP interface was studied by high-resolution X-ray photoelectron spectroscopy. The results indicated that the silicon interfacial layer reacted with the native oxide at the InP surface, thus producing silicon dioxide, while reducing the native oxide which has been shown to be responsible for the instabilities in InP MISFETs. While a 1.2-V hysteresis was present in the capacitance-voltage (C-V) curve of the MIS capacitors with silicon dioxide, less than 0.1 V hysteresis was observed in the C-V curve of the capacitors with the silicon interfacial layer incorporated in the insulator. InP MISFETs fabricated with the silicon dioxide in combination with the silicon interfacial layer exhibited excellent stability with drain current drift of less than 3 percent in 10,000 sec, as compared to 15-18 percent drift in 10,000 sec for devices without the silicon interfacial layer. High-power microwave InP MISFETs with Si/SiO2 gate insulators resulted in an output power density of 1.75 W/mm gate width at 9.7 GHz, with an associated power gain of 2.5 dB and 24 percent power added efficiency.

  19. Effect of annealing temperature on the electrical properties of Au/Ta{sub 2}O{sub 5}/n-GaN metal-insulator-semiconductor (MIS) structure

    Energy Technology Data Exchange (ETDEWEB)

    Prasanna Lakshmi, B.; Rajagopal Reddy, V.; Janardhanam, V. [Sri Venkateswara University, Department of Physics, Tirupati (India); Siva Pratap Reddy, M.; Lee, Jung-Hee [Kyungpook National University, School of Electrical Engineering and Computer Science, Daegu (Korea, Republic of)

    2013-11-15

    We report on the effect of an annealing temperature on the electrical properties of Au/Ta{sub 2}O{sub 5}/n-GaN metal-insulator-semiconductor (MIS) structure by current-voltage (I-V) and capacitance-voltage (C-V) measurements. The measured Schottky barrier height ({Phi} {sub bo}) and ideality factor n values of the as-deposited Au/Ta{sub 2}O{sub 5}/n-GaN MIS structure are 0.93 eV (I-V) and 1.19. The barrier height (BH) increases to 1.03 eV and ideality factor decreases to 1.13 upon annealing at 500 {sup circle} C for 1 min under nitrogen ambient. When the contact is annealed at 600 {sup circle} C, the barrier height decreases and the ideality factor increases to 0.99 eV and 1.15. The barrier heights obtained from the C-V measurements are higher than those obtained from I-V measurements, and this indicates the existence of spatial inhomogeneity at the interface. Cheung's functions are also used to calculate the barrier height ({Phi} {sub bo}), ideality factor (n), and series resistance (R{sub s}) of the Au/Ta{sub 2}O{sub 5}/n-GaN MIS structure. Investigations reveal that the Schottky emission is the dominant mechanism and the Poole-Frenkel emission occurs only in the high voltage region. The energy distribution of interface states is determined from the forward bias I-V characteristics by taking into account the bias dependence of the effective barrier height. It is observed that the density value of interface states for the annealed samples with interfacial layer is lower than that of the density value of interface states of the as-deposited sample. (orig.)

  20. Theory of field induced incommensurability: CsFeCl3

    DEFF Research Database (Denmark)

    Lindgård, Per-Anker

    1986-01-01

    Using correlation theory for the singlet-doublet magnet CsFeCl3 in a magnetic field, a field induced incommensurate ordering along K-M is predicted without invoking dipolar effects. A fully self-consistent RPA theory gives Hc=44 kG in agreement with experiments at T=1.3K. Correlation and dipolar ...

  1. Field-Induced Superconductivity in Electric Double Layer Transistors

    NARCIS (Netherlands)

    Ueno, Kazunori; Shimotani, Hidekazu; Yuan, Hongtao; Ye, Jianting; Kawasaki, Masashi; Iwasa, Yoshihiro

    2014-01-01

    Electric field tuning of superconductivity has been a long-standing issue in solid state physics since the invention of the field-effect transistor (FET) in 1960. Owing to limited available carrier density in conventional FET devices, electric-field-induced superconductivity was believed to be possi

  2. Field-Induced CDW Phases in a Quasi-One-Dimensional Organic Conductor, HMTSF-TCNQ Under Pressure of 1 GPa in Magnetic Field of 31 T

    Science.gov (United States)

    Murata, K.; Kang, W.; Masuda, K.; Fukumoto, Y.; Graf, D.; Kiswandhi, A.; Choi, E. S.; Brooks, J. S.; Sasaki, T.; Yokogawa, K.; Yoshino, H.; Kato, R.

    2013-03-01

    HMTSF-TCNQ is a quasi-one-dimensional organic conductor which undergoes CDW(charge density wave) transition at 30 K at ambient pressure, where HMTSF-TCNQ is hexamethylenetetraselena fulvalene-tetracyano quino dimethane. This CDW is suppressed by the pressure of 1 GPa. At this pressure, we found field-induced successive hysteretic transitions in magnetoresistance. This reminds us of the successive field-induced SDW (spin density wave) phases in TMTSF2X salts. However, the field range of interest is 2-3 times higher than that of TMTSF2X salts. Therefore, we need really high field to examine these properties. It is very likely that the field induced phases are of field induced CDW (FICDW), where quantum Hall effect and many interesting phenomena are expected like in the case of FISDW. Together with the magnetoresistance study up to the field of 31 Tesla and at temperatures down to 0.4 K in various magnetic field angles respective to the crystal axes, we examined the angular dependence of magnetoresistance oscillations(AMRO). It turned out that AMRO demonstrates clearly the occurrence of field-induced phase rather than the magneto-resistance by field sweep. Since the Hall resistance, R xy in the field-induced phases showed stepwise plateau structure against the field sweep, and its strength was in the order of magnitude of h/ e 2 per molecular sheet, the Hall effect is very suggestive of quantum Hall effect.

  3. Field-induced exciton condensation in LaCoO3

    Science.gov (United States)

    Sotnikov, A.; Kuneš, J.

    2016-07-01

    Motivated by recent observation of magnetic field induced transition in LaCoO3 we study the effect of external field in systems close to instabilities towards spin-state ordering and exciton condensation. We show that, while in both cases the transition can be induced by an external field, temperature dependencies of the critical field have opposite slopes. Based on this result we argue that the experimental observations select the exciton condensation scenario. We show that such condensation is possible due to high mobility of the intermediate spin excitations. The estimated width of the corresponding dispersion is large enough to overrule the order of atomic multiplets and to make the intermediate spin excitation propagating with a specific wave vector the lowest excitation of the system.

  4. Sodium beta-alumina thin films as gate dielectrics for AlGaN/GaN metal-insulator-semiconductor high-electron-mobility transistors

    Institute of Scientific and Technical Information of China (English)

    Tian Ben-Lang; Chen Chao; Li Yan-Rong; Zhang Wan-Li; Liu Xing-Zhao

    2012-01-01

    Sodium beta-alumina (SBA) is deposited on AlGaN/GaN by using a co-deposition process with sodium and Al2O3 as the precursors.The X-ray diffraction (XRD) spectrum reveals that the deposited thin film is amorphous.The binding energy and composition of the deposited thin film,obtained from the X-ray photoelectron spectroscopy (XPS)measurement,are consistent with those of SBA.The dielectric constant of the SBA thin film is about 50.Each of the capacitance-voltage characteristics obtained at five different frequencies shows a high-quality interface between SBA and A1GaN.The interface trap density of metal-insulator-semiconductor high-electron-mobility transistor (MISHEMT)is measured to be (3.5~9.5)× 1010 cm-2.eV-1 by the conductance method.The fixed charge density of SBA dielectric is on the order of 2.7x1012 cm-2.Compared with the AlGaN/GaN metal semiconductor hetcrostructure high-electron-mobility transistor (MESHEMT),the AlGaN/GaN MISHEMT usually has a threshold voltage that shifts negatively.However,the threshold voltage of the AlGaN/GaN MISHEMT using SBA as the gate dielectric shifts positively from -5.5 V to-3.5 V.From XPS results,the surface valence-band maximum (VBM-EF) of AlGaN is found to decrease from 2.56 eV to 2.25 eV after the SBA thin film deposition.The possible reasons why the threshold voltage of AlGaN/GaN MISHEMT with the SBA gate dielectric shifts positively are the influence of SBA on surface valence-band maximum (VBM-EF),the reduction of interface traps and the effects of sodium ions,and/or the fixed charges in SBA on the two-dimensional electron gas (2DEG).

  5. Environmentally stable flexible metal-insulator-metal capacitors using zirconium-silicate and hafnium-silicate thin film composite materials as gate dielectrics.

    Science.gov (United States)

    Meena, Jagan Singh; Chu, Min-Ching; Wu, Chung-Shu; Ravipati, Srikanth; Ko, Fu-Hsiang

    2011-08-01

    Fully flexible metal-insulator-metal (MIM) capacitors fabricated on 25 microm thin polyimide (PI) substrates via the surface sol-gel process using 10-nm-thick zirconium-silicate (ZrSixOy) and hafnium-silicate (HfSimOn) films as gate dielectrics. The surface morphology of the ZrSixOy and HfSimOn films were investigated using atomic force microscopy and scanning electron microscopy, which confirmed that continuous and crack-free surface growth had occurred on the PI. Both the films treated with oxygen (O2) plasma and annealing (ca. 250 degrees C) consisted of amorphous phase; confirmed by X-ray diffraction. We employed X-ray photoelectron spectroscopy (XPS) at high resolution to examine the chemical composition of the films subjected to various treatment conditions. The shift of the XPS peaks towards higher binding energy revealed the O2 plasma-pretreatment followed by annealing was the most effective process to the surface oxidation at relatively low-temperature, for further passivate the grease traps and making dielectric films thermally stable. The ZrSixOy and HfSimOn films in sandwich-like MIM configuration on the PI substrates exhibited the low leakage current densities of 7.1 x 10(-9) and 8.4 x 10(-9) A/cm2 at applied electric field of 10 MV/cm and maximum capacitance densities of 7.5 and 5.3 fF/microm2 at 1 MHz, respectively. In addition, the ZrSixOy and HfSimOn films in MIM capacitors showed the estimated dielectric constants of 8.2 and 6.0, respectively. Prior to use of flexible MIM capacitors in advanced flexible electronic devices; the reliability test was studied by applying day-dependent leakage current density measurements up to 30 days. These films of silicate-surfactant mesostructured materials have special interest to be used as gate dielectrics in future for flexible metal-oxide-semiconductor devices.

  6. Conduction and rectification in NbO x - and NiO-based metal-insulator-metal diodes

    Energy Technology Data Exchange (ETDEWEB)

    Osgood, Richard M.; Giardini, Stephen; Carlson, Joel; Periasamy, Prakash; Guthrey, Harvey; O' Hayre, Ryan; Chin, Matthew; Nichols, Barbara; Dubey, Madan; Fernandes, Gustavo; Kim, Jin Ho; Xu, Jimmy; Parilla, Philip; Berry, Joseph; Ginley, David

    2016-09-01

    Conduction and rectification in nanoantenna-coupled NbOx- and NiO-based metal-insulator-metal (MIM) diodes ('nanorectennas') are studied by comparing new theoretical predictions with the measured response of nanorectenna arrays. A new quantum mechanical model is reported and agrees with measurements of current-voltage (I-V) curves, over 10 orders of magnitude in current density, from [NbOx(native)-Nb2O5]- and NiO-based samples with oxide thicknesses in the range of 5-36 nm. The model, which introduces new physics and features, including temperature, electron effective mass, and image potential effects using the pseudobarrier technique, improves upon widely used earlier models, calculates the MIM diode's I-V curve, and predicts quantitatively the rectification responsivity of high frequency voltages generated in a coupled nanoantenna array by visible/near-infrared light. The model applies both at the higher frequencies, when high-energy photons are incident, and at lower frequencies, when the formula for classical rectification, involving derivatives of the I-V curve, may be used. The rectified low-frequency direct current is well-predicted in this work's model, but not by fitting the experimentally measured I-V curve with a polynomial or by using the older Simmons model (as shown herein). By fitting the measured I-V curves with our model, the barrier heights in Nb-(NbOx(native)-Nb2O5)-Pt and Ni-NiO-Ti/Ag diodes are found to be 0.41/0.77 and 0.38/0.39 eV, respectively, similar to literature reports, but with effective mass much lower than the free space value. The NbOx (native)-Nb2O5 dielectric properties improve, and the effective Pt-Nb2O5 barrier height increases as the oxide thickness increases. An observation of direct current of ~4 nA for normally incident, focused 514 nm continuous wave laser beams are reported, similar in magnitude to recent reports. This measured direct current is compared to the prediction for rectified direct current

  7. Analysis of temperature dependent current-conduction mechanisms in Au/TiO2/n-4H-SiC (metal/insulator/semiconductor) type Schottky barrier diodes

    Science.gov (United States)

    Alialy, S.; Altındal, Ş.; Tanrıkulu, E. E.; Yıldız, D. E.

    2014-08-01

    In order to determine the effective current-conduction mechanisms in Au/TiO2/n-4H-SiC (metal-insulator semiconductor) type Schottky barrier diodes (SBDs), their current-voltage (I-V) measurements were carried out in the temperature range of 200-380 K. Some electrical parameters, such as ideality factor (n), zero-bias barrier height (BH) (ΦBo), series and shunt resistances (Rs, Rsh), were obtained as 5.09, 0.81 eV, 37.43 Ω, and 435 kΩ at 200 K and 2.68, 0.95 eV, 5.99 Ω, and 73 kΩ at 380 K, respectively. The energy density distribution profile of surface states (Nss) was extracted from the forward-bias I-V data by taking into account voltage dependent of the ideality factor (nV), effective BH (Φe), and Rs for 200, 300, and 380 K. The Ln(I) vs V plots are completely parallel in the intermediate bias voltages, which may be well explained by field emission (FE) mechanism for each temperature. On the other hand, the high value of n cannot be explained with this mechanism. Therefore, to explain the change in BH and n with temperature, ΦBo vs q/2kT plot was drawn to obtain an evidence of a Gaussian distribution (GD) of the BHs and thus the mean value of BH (Φ¯Bo) and standard deviation (σso) values were found from this plot as 1.396 eV and 0.176 V, respectively. The Φ¯Bo and Richardson constant (A*) values were found as 1.393 eV and 145.5 A.cm-2 K-2 using modified Ln(Io/T2)-(q2σs2/2k2T2) vs q/kT plot, respectively. It is clear that all of the obtained main electrical parameters were found as a strong function of temperature. These results indicated that the current conduction mechanism in Au/TiO2/n-4 H-SiC (SBD) well obey the FE and GD mechanism rather than other mechanisms.

  8. The transition to the metallic state in low density hydrogen.

    Science.gov (United States)

    McMinis, Jeremy; Morales, Miguel A; Ceperley, David M; Kim, Jeongnim

    2015-11-21

    Solid atomic hydrogen is one of the simplest systems to undergo a metal-insulator transition. Near the transition, the electronic degrees of freedom become strongly correlated and their description provides a difficult challenge for theoretical methods. As a result, the order and density of the phase transition are still subject to debate. In this work, we use diffusion quantum Monte Carlo to benchmark the transition between paramagnetic and anti-ferromagnetic body centered cubic atomic hydrogen in its ground state. We locate the density of the transition by computing the equation of state for these two phases and identify the phase transition order by computing the band gap near the phase transition. These benchmark results show that the phase transition is continuous and occurs at a Wigner-Seitz radius of rs = 2.27(3) a0. We compare our results to previously reported density functional theory, Hedin's GW approximation, and dynamical mean field theory results.

  9. Electric field-induced softening of alkali silicate glasses

    Energy Technology Data Exchange (ETDEWEB)

    McLaren, C.; Heffner, W.; Jain, H. [Department of Materials Science and Engineering, Lehigh University, Bethlehem, Pennsylvania 18015 (United States); Tessarollo, R.; Raj, R. [Department of Mechanical Engineering, University of Colorado at Boulder, Boulder, Colorado 80309 (United States)

    2015-11-02

    Motivated by the advantages of two-electrode flash sintering over normal sintering, we have investigated the effect of an external electric field on the viscosity of glass. The results show remarkable electric field-induced softening (EFIS), as application of DC field significantly lowers the softening temperature of glass. To establish the origin of EFIS, the effect is compared for single vs. mixed-alkali silicate glasses with fixed mole percentage of the alkali ions such that the mobility of alkali ions is greatly reduced while the basic network structure does not change much. The sodium silicate and lithium-sodium mixed alkali silicate glasses were tested mechanically in situ under compression in external electric field ranging from 0 to 250 V/cm in specially designed equipment. A comparison of data for different compositions indicates a complex mechanical response, which is observed as field-induced viscous flow due to a combination of Joule heating, electrolysis and dielectric breakdown.

  10. Electric field-induced softening of alkali silicate glasses

    Science.gov (United States)

    McLaren, C.; Heffner, W.; Tessarollo, R.; Raj, R.; Jain, H.

    2015-11-01

    Motivated by the advantages of two-electrode flash sintering over normal sintering, we have investigated the effect of an external electric field on the viscosity of glass. The results show remarkable electric field-induced softening (EFIS), as application of DC field significantly lowers the softening temperature of glass. To establish the origin of EFIS, the effect is compared for single vs. mixed-alkali silicate glasses with fixed mole percentage of the alkali ions such that the mobility of alkali ions is greatly reduced while the basic network structure does not change much. The sodium silicate and lithium-sodium mixed alkali silicate glasses were tested mechanically in situ under compression in external electric field ranging from 0 to 250 V/cm in specially designed equipment. A comparison of data for different compositions indicates a complex mechanical response, which is observed as field-induced viscous flow due to a combination of Joule heating, electrolysis and dielectric breakdown.

  11. Field induced spin chirality and chirality switching in magnetic multilayers

    Energy Technology Data Exchange (ETDEWEB)

    Tartakovskaya, Elena V., E-mail: elena_tartakovskaya@yahoo.com [Institute of Magnetism NAS of Ukraine, Vernadsky blvd 36b, 03142 Kiev (Ukraine); Institute of High Technologies, Taras Shevchenko National University of Kiev, 03022 Kiev (Ukraine)

    2015-05-01

    The physical origin of the field-induced spin chirality experimentally observed in rare earth multilayers is determined. It is shown that the effect is possible due to the interplay between solid-state exchange interactions (the Ruderman–Kittel–Kasuya–Yosida and the Dsyaloshinsky–Moriya interactions), the external magnetic field and a special confinement of magnetic constituents. The presented model describes a certain temperature dependence of the chirality factor in agreement with experimental data and opens a new way to design nanostructured objects with predicted handedness. - Highlights: • Field-induced spin chirality in magnetic multilayers is explained. • The roles of the RKKY, the DM and the Zeeman interactions are clarified. • Theoretical analysis of the chirality factor is in agreement with experimental data.

  12. Magnetic field induced optical gain in a dilute nitride quaternary semiconductor quantum dot

    Science.gov (United States)

    Mageshwari, P. Uma; Peter, A. John; Lee, Chang Woo

    2016-10-01

    Effects of magnetic field strength on the electronic and optical properties are brought out in a Ga0.661In0.339N0.0554As0.9446/GaAs quantum dot for the applications of desired wavelength in opto-electronic devices. The band alignment is obtained using band anticrossing model and the model solid theory. The magnetic field dependent electron-heavy hole transition energies with the dot radius in a GaInNAs/GaAs quantum dot are investigated. The magnetic field induced oscillator strength as a function of dot radius is studied. The resonant peak values of optical absorption coefficients and the changes of refractive index with the application of magnetic field strength in a GaInNAs/GaAs quantum dot are obtained. The magnetic field induced threshold current density and the maximum optical gain are found in a GaInNAs/GaAs quantum dot. The results show that the optimum wavelength for fibre optical communication networks can be obtained with the variation of applied magnetic field strength and the outcomes may be useful for the design of efficient lasers based on the group III-N-V semiconductors.

  13. Electric field induced strain, switching and energy storage behaviour of lead free Barium Zirconium Titanate ceramic

    Science.gov (United States)

    Badapanda, T.; Chaterjee, S.; Mishra, Anupam; Ranjan, Rajeev; Anwar, S.

    2017-09-01

    There is a huge demand of lead-free high performance ceramics with large strain, low hysteresis loss and high-energy storage ability at room temperature. In this context, we investigated the large electric field induced strain, switching behaviour and energy storage properties of BaZr0.05Ti0.95O3 ceramic (BZT) prepared by high energy ball milling technique, reportedly exhibiting a triple point transition near the room temperature. The X-ray diffraction of the BZT ceramic confirms orthorhombic symmetry with space group Amm2 at room temperature. The room temperature dielectric study reveals that there is a negligible variation of dielectric constant and dielectric loss with frequency. The polarization behaviour at various applied electric fields was studied and the energy storage densities were obtained from the integral area of P-E loops. Electric field induced strain behaviour has been studied with due emphasis on the electrostrictive response at room temperature. The ferroelectric and electromechanical properties derived from the P-E and S-E loops suggest that the present ceramic encompass the properties of actuation and energy storage simultaneously.

  14. Field induced spin chirality and chirality switching in magnetic multilayers

    Science.gov (United States)

    Tartakovskaya, Elena V.

    2015-05-01

    The physical origin of the field-induced spin chirality experimentally observed in rare earth multilayers is determined. It is shown that the effect is possible due to the interplay between solid-state exchange interactions (the Ruderman-Kittel-Kasuya-Yosida and the Dsyaloshinsky-Moriya interactions), the external magnetic field and a special confinement of magnetic constituents. The presented model describes a certain temperature dependence of the chirality factor in agreement with experimental data and opens a new way to design nanostructured objects with predicted handedness.

  15. Modeling large reversible electric-field-induced strain in ferroelectric materials using 90° orientation switching

    Institute of Scientific and Technical Information of China (English)

    WANG LinXiang; LIU Rong; Roderick V.N.MELNIK

    2009-01-01

    Reversible large electric-field-induced strain caused by reversible orientation switchings in BaTiO3 is modeled using the Landau's theory of phase transition. A triple well free energy function is constructed, Each of its minima is associated with one of the polarization orientations involved, Nonlinear constitu-tive laws accounting for reversible orientation switchings and electrostriction effects are obtained by using thermodynamic equilibrium conditions. Hysteretic dynamics of one-dimensional structures is described by coupled nonlinear differential equations. Double hysteretic loops in the electric and me-chanic fields are both successfully modeled. Giant reversible electrostriction is modeled as a conse-quence of reversible orientation switchings via electro-mechanical couplings. Comparisons with ex-perimental results reported in literatures are presented.

  16. Field-induced spin-density wave beyond hidden order in URu2Si2

    Science.gov (United States)

    Knafo, W.; Duc, F.; Bourdarot, F.; Kuwahara, K.; Nojiri, H.; Aoki, D.; Billette, J.; Frings, P.; Tonon, X.; Lelièvre-Berna, E.; Flouquet, J.; Regnault, L.-P.

    2016-10-01

    URu2Si2 is one of the most enigmatic strongly correlated electron systems and offers a fertile testing ground for new concepts in condensed matter science. In spite of >30 years of intense research, no consensus on the order parameter of its low-temperature hidden-order phase exists. A strong magnetic field transforms the hidden order into magnetically ordered phases, whose order parameter has also been defying experimental observation. Here, thanks to neutron diffraction under pulsed magnetic fields up to 40 T, we identify the field-induced phases of URu2Si2 as a spin-density-wave state. The transition to the spin-density wave represents a unique touchstone for understanding the hidden-order phase. An intimate relationship between this magnetic structure, the magnetic fluctuations and the Fermi surface is emphasized, calling for dedicated band-structure calculations.

  17. Modeling large reversible electric-field-induced strain in ferroelectric materials using 90° orientation switching

    Institute of Scientific and Technical Information of China (English)

    Roderick; V.; N.; MELNIK

    2009-01-01

    Reversible large electric-field-induced strain caused by reversible orientation switchings in BaTiO3 is modeled using the Landau’s theory of phase transition. A triple well free energy function is constructed. Each of its minima is associated with one of the polarization orientations involved. Nonlinear constitu- tive laws accounting for reversible orientation switchings and electrostriction effects are obtained by using thermodynamic equilibrium conditions. Hysteretic dynamics of one-dimensional structures is described by coupled nonlinear differential equations. Double hysteretic loops in the electric and me- chanic fields are both successfully modeled. Giant reversible electrostriction is modeled as a conse-quence of reversible orientation switchings via electro-mechanical couplings. Comparisons with ex-perimental results reported in literatures are presented.

  18. Dispersion of Electric-Field-Induced Faraday Effect in Magnetoelectric Cr2O3

    Science.gov (United States)

    Wang, Junlei; Binek, Christian

    2016-03-01

    The frequency dependence of the electric-field-induced magneto-optical Faraday effect is investigated in the magnetoelectric antiferromagnet chromia. Two electrically induced Faraday signals superimpose in proportion to the linear magnetoelectric susceptibility α and the antiferromagnetic order parameter η . The relative strength of these contributions is determined by the frequency of the probing light and can be tuned between extreme characteristics following the temperature dependence of α or η . The frequency dependence is analyzed in terms of electric dipole transitions of perturbed Cr3 + crystal-field states. The results allow us to measure voltage-controlled selection, isothermal switching, and temperature dependence of η in a tabletop setup. The voltage-specific Faraday rotation is independent of the sample thickness, making the method scalable and versatile down to the limit of dielectric breakdown.

  19. Magnetic field induced switching of the antiferromagnetic order parameter in thin films of magnetoelectric chromia

    Science.gov (United States)

    Fallarino, Lorenzo; Berger, Andreas; Binek, Christian

    2015-02-01

    A Landau-theoretical approach is utilized to model the magnetic field induced reversal of the antiferromagnetic order parameter in thin films of magnetoelectric antiferromagnets. A key ingredient of this peculiar switching phenomenon is the presence of a robust spin polarized state at the surface of the antiferromagnetic films. Surface or boundary magnetization is symmetry allowed in magnetoelectric antiferromagnets and experimentally established for chromia thin films. It couples rigidly to the antiferromagnetic order parameter and its Zeeman energy creates a pathway to switch the antiferromagnet via magnetic field application. In the framework of a minimalist Landau free energy expansion, the temperature dependence of the switching field and the field dependence of the transition width are derived. Least-squares fits to magnetometry data of (0001 ) textured chromia thin films strongly support this model of the magnetic reversal mechanism.

  20. Electric field induced domain-wall dynamics: Depinning and chirality switching

    Science.gov (United States)

    Upadhyaya, Pramey; Dusad, Ritika; Hoffman, Silas; Tserkovnyak, Yaroslav; Alzate, Juan G.; Amiri, Pedram Khalili; Wang, Kang L.

    2013-12-01

    We theoretically study the equilibrium and dynamic properties of nanoscale magnetic tunnel junctions (MTJs) and magnetic wires, in which an electric field controls the magnetic anisotropy through spin-orbit coupling. By performing micromagnetic simulations, we construct a rich phase diagram and find that, in particular, the equilibrium magnetic textures can be tuned between Néel and Bloch domain walls in an elliptical MTJ. Furthermore, we develop a phenomenological model of a quasi-one-dimensional domain wall confined by a parabolic potential and show that, near the Néel-to-Bloch-wall transition, a pulsed electric field induces precessional domain-wall motion which can be used to reverse the chirality of a Néel wall and even depin it. This domain-wall motion controlled by electric fields, in lieu of applied current, may provide a model for ultralow-power domain-wall memory and logic devices.

  1. Dynamics of electric field induced particle alignment in nonpolar polymer matrix

    Science.gov (United States)

    Tai, Xiangyang; Wu, Guozhang; Yui, Hiroshi; Asai, Shigeo; Sumita, Masao

    2003-11-01

    The dynamics of electric field induced particle alignment in nonpolar polymer matrix to build one-dimensional conductive materials was investigated. The influence of electric field on particle alignment was real-time traced by dynamic percolation measurement using carbon black (CB) filled polyethylene as a model system. The activation energy of the continuous CB path formation was calculated and found to be unchanged with CB alignment. The critical percolation concentration at thermodynamic equilibrium state φc* was deduced to characterize the anisotropism of network structure, by which the thermodynamic prerequisite electric field E* for the transition from three-dimensional isotropic network to one-dimensional chain could be easily found out.

  2. Magnetic-field-induced shape recovery by reverse phase transformation.

    Science.gov (United States)

    Kainuma, R; Imano, Y; Ito, W; Sutou, Y; Morito, H; Okamoto, S; Kitakami, O; Oikawa, K; Fujita, A; Kanomata, T; Ishida, K

    2006-02-23

    Large magnetic-field-induced strains have been observed in Heusler alloys with a body-centred cubic ordered structure and have been explained by the rearrangement of martensite structural variants due to an external magnetic field. These materials have attracted considerable attention as potential magnetic actuator materials. Here we report the magnetic-field-induced shape recovery of a compressively deformed NiCoMnIn alloy. Stresses of over 100 MPa are generated in the material on the application of a magnetic field of 70 kOe; such stress levels are approximately 50 times larger than that generated in a previous ferromagnetic shape-memory alloy. We observed 3 per cent deformation and almost full recovery of the original shape of the alloy. We attribute this deformation behaviour to a reverse transformation from the antiferromagnetic (or paramagnetic) martensitic to the ferromagnetic parent phase at 298 K in the Ni45Co5Mn36.7In13.3 single crystal.

  3. Temperature and electric-field induced phase transitions, and full tensor properties of [011] C-poled domain-engineered tetragonal 0 .63 Pb (M g1 /3N b2 /3) -0 .37 PbTi O3 single crystals

    Science.gov (United States)

    Zheng, Limei; Jing, Yujia; Lu, Xiaoyan; Wang, Ruixue; Liu, Gang; Lü, Weiming; Zhang, Rui; Cao, Wenwu

    2016-03-01

    The phase-transition sequence of 0.67 Pb (M g1 /3N b2 /3)- 0.37 PbTi O3 (PMN-0.37PT) single crystals driven by the electric (E ) field and temperature is comprehensively studied. Based on the strain-E field loop, polarization-E field loop, and the evolution of domain configurations, the E field along the [011] C induced phase transitions have been confirmed to be as follows: tetragonal (T ) → monoclinic (MC)→ single domain orthorhombic (O ) phase. As the E field decreases, the induced O phase cannot be maintained and transformed to the MC phase, then to the coexistence state of MC and T phases. In addition, the complete sets of dielectric, piezoelectric, and elastic constants for the [011] C-poled domain-engineered PMN-0.37PT single crystal were measured at room temperature, which show high longitudinal dielectric, piezoelectric, and electromechanical properties (ɛ33T=10 661 ,d33=1052 pC /N , and k33= 0.766 ). Our results revealed that the MC phase plays an important role in the high electromechanical properties of this domain-engineered single crystal. The temperature dependence of the domain configuration revealed that the volume fraction of the MC phase decreases with temperature accompanied by the reduction of ɛ33T,d31, and k31 due to the substantially smaller intrinsic properties of the T phase.

  4. 基于FTO/VO2/FTO结构的VO2薄膜电压诱导相变光调制特性∗%Optical mo dulation characteristics of VO2 thin film due to electric field induced phase transition in the FTO/VO2/FTO structure

    Institute of Scientific and Technical Information of China (English)

    郝如龙; 方宝英; 王晓华; 肖寒; 李毅; 刘飞; 孙瑶; 唐佳茵; 陈培祖; 蒋蔚; 伍征义; 徐婷婷

    2015-01-01

    VO2 thin films have been studied for their semiconductor–metal reversible transition from the monoclinic to the rutile structure, where the electrical and optical properties undergo a drastic change by increasing the temperature or by applying a voltage. VO2 film is becoming a promising material for optical switch, optical storage, optical modulator, smart window, and micro-bolometer. The preparation procedures of the FTO/VO2/FTO structure in detail are as follows:First, the F-doped SnO2 conductive glass (FTO) substrates are cleaned sequentially in acetone, ethanol, and deionized water for 10 min using an ultrasonic cleaning equipment at a frequency of 20 kHz. When the FTO substrates was cleaned, they are dried with nitrogen. Second, the dried FTO substrates are placed in the chamber of a DC magnetron sputtering system equipped with a high-purity metal target of V (99.9%). After argon (99.999%) of 80 sccm flux was discharged with the current of 2 A and the voltage of 400 V for 2 min, the vanadium films are deposited on the FTO substrates. Third, the prepared vanadium films are annealed for different annealing time in an atmosphere composed of different proportions of nitrogen-oxygen. Then another layer thickness of 350 nm of FTO conductive film is deposited on the VO2 thin film by using the plasma enhanced chemical vapor deposition method. Finally, different sizes of the FTO/VO2/FTO structure are prepared by using photolithography and chemical etching processes. The effect of different annealing time and different proportions of nitrogen-oxygen atmosphere on the VO2 thin films has been studied. X-ray diffraction (XRD), scanning electron microscope (SEM), atomic force microscope (AFM), X-ray photoelectron spectroscopy (XPS) and spectrophotometer are then used to test and analyze the crystal structure, surface morphology, surface roughness, the relative content of the surface elements, and transmittance of the VO2/FTO composite films. Results show that a relatively

  5. Physical and electrical properties of induced high-k ZrHfO crystallization with ZrN cap by high power impulse magnetron sputtering for metal-gate metal-insulator-semiconductor structures

    Science.gov (United States)

    Tsai, Jung-Ruey; Juan, Pi-Chun; Lin, Cheng-Li; Lin, Guo-Cheng

    2017-01-01

    Metal-gate TiN/ZrN/ZrHfO/p-Si metal-insulator-semiconductor (MIS) structures have been fabricated in this work. The physical and electrical properties were characterized. The crystallization of high-k ZrHfO thin-film is induced by high power impulse magnetron sputtering (HIPIMS) during the deposition of ZrN capping layer. The binding energies and depth profiles were investigated by X-ray photoelectron spectroscopy (XPS). It is found that Zr and Hf out-diffusion from high-k dielectric in samples with HIPIMS is lesser than those in samples with the conventional DC magnetron sputtering (DCMS). The dielectric constant which strongly relates to the tetragonal phase becomes higher and the flatband voltage shift shows smaller by using the HIPIMS method than by the conventional DCMS. The cation and anion vacancies have been investigated by the defect reaction model.

  6. Fabrication of normally-off AlGaN/GaN metal-insulator-semiconductor high-electron-mobility transistors by photo-electrochemical gate recess etching in ionic liquid

    Science.gov (United States)

    Zhang, Zhili; Qin, Shuangjiao; Fu, Kai; Yu, Guohao; Li, Weiyi; Zhang, Xiaodong; Sun, Shichuang; Song, Liang; Li, Shuiming; Hao, Ronghui; Fan, Yaming; Sun, Qian; Pan, Gebo; Cai, Yong; Zhang, Baoshun

    2016-08-01

    We characterized an ionic liquid (1-butyl-3-methylimidazolium nitrate, C8H15N3O3) as a photo-electrochemical etchant for fabricating normally-off AlGaN/GaN metal-insulator-semiconductor high-electron-mobility transistors (MIS-HEMTs). Using the ionic liquid, we achieved an etching rate of ˜2.9 nm/min, which is sufficiently low to facilitate good etching control. The normally-off AlGaN/GaN MIS-HEMT was fabricated with an etching time of 6 min, with the 20 nm low-pressure chemical vapor deposition (LPCVD) silicon nitride (Si3N4) gate dielectric exhibiting a threshold voltage shift from -10 to 1.2 V, a maximum drain current of more than 426 mA/mm, and a breakdown voltage of 582 V.

  7. Ground-state oxygen holes and the metal–insulator transition in the negative charge-transfer rare-earth nickelates

    OpenAIRE

    Bisogni, Valentina; Catalano, Sara; Green, Robert J.; Gibert, Marta; Scherwitzl, Raoul; Huang, Yaobo; Strocov, Vladimir N.; Zubko, Pavlo; Balandeh, Shadi; Triscone, Jean-Marc; Sawatzky, George; Schmitt, Thorsten

    2016-01-01

    The metal-insulator transitions and the intriguing physical properties of rare-earth perovskite nickelates have attracted considerable attention in recent years. Nonetheless, a complete understanding of these materials remains elusive. Here, taking a NdNiO3 thin film as a representative example, we utilize a combination of x-ray absorption and resonant inelastic x-ray scattering (RIXS) spectroscopies to resolve important aspects of the complex electronic structure of the rare-earth nickelates...

  8. Magnetic Fields Induced in the Solid Earth and Oceans

    DEFF Research Database (Denmark)

    Kuvshinov, Alexei; Olsen, Nils

    Electromagnetic induction in the Earth's interior is an important contributor to the near-Earth magnetic field. Oceans play a special role in the induction, due to their relatively high conductance of large lateral variability. Electric currents that generate secondary magnetic fields are induced...... in the oceans by two different sources: by time varying external magnetic fields, and by motion of the conducting ocean water through the Earth's main magnetic field. Significant progress in the accurate and detailed prediction of magnetic fields induced by these sources has been achieved during the last years......, utilizing realistic 3-D conductivity models of the oceans, crust and mantle. In addition to these improvements in the prediction of 3-D induction effects, much attention has been paid to identifying magnetic signals of oceanic origin in observatory and satellite data. During the talk we will present...

  9. Direct observations of field-induced assemblies in magnetite ferrofluids

    Science.gov (United States)

    Mousavi, N. S. Susan; Khapli, Sachin D.; Kumar, Sunil

    2015-03-01

    Evolution of microstructures in magnetite-based ferrofluids with weak dipolar moments (particle size ≤ 10 nm) is studied with an emphasis on examining the effects of particle concentration (ϕ) and magnetic field strength (H) on the structures. Nanoparticles are dispersed in water at three different concentrations, ϕ = 0.15%, 0.48%, and 0.59% (w/v) [g/ml%] and exposed to uniform magnetic fields in the range of H = 0.05-0.42 T. Cryogenic transmission electron microscopy is employed to provide in-situ observations of the field-induced assemblies in such systems. As the magnetic field increases, the Brownian colloids are observed to form randomly distributed chains aligned in the field direction, followed by head-to-tail chain aggregation and then lateral aggregation of chains termed as zippering. By increasing the field in low concentration samples, the number of chains increases, though their length does not change dramatically. Increasing concentration increases the length of the linear particle assemblies in the presence of a fixed external magnetic field. Thickening of the chains due to zippering is observed at relatively high fields. Through a systematic variation of concentration and magnetic field strength, this study shows that both magnetic field strength and change in concentration can strongly influence formation of microstructures even in weak dipolar systems. Additionally, the results of two commonly used support films on electron microscopy grids, continuous carbon and holey carbon films, are compared. Holey carbon film allows us to create local regions of high concentrations that further assist the development of field-induced assemblies. The experimental observations provide a validation of the zippering effect and can be utilized in the development of models for thermophysical properties such as thermal conductivity.

  10. Direct observations of field-induced assemblies in magnetite ferrofluids

    Energy Technology Data Exchange (ETDEWEB)

    Mousavi, N. S. Susan [Mechanical Engineering Department, Polytechnic School of Engineering, New York University, 6 Metrotech Center, Brooklyn, New York 11201 (United States); Khapli, Sachin D. [New York University Abu Dhabi, Saadiyat Island, PO Box 129 188, Abu Dhabi (United Arab Emirates); Kumar, Sunil [Mechanical Engineering Department, Polytechnic School of Engineering, New York University, 6 Metrotech Center, Brooklyn, New York 11201 (United States); New York University Abu Dhabi, Saadiyat Island, PO Box 129 188, Abu Dhabi (United Arab Emirates)

    2015-03-14

    Evolution of microstructures in magnetite-based ferrofluids with weak dipolar moments (particle size ≤ 10 nm) is studied with an emphasis on examining the effects of particle concentration (ϕ) and magnetic field strength (H) on the structures. Nanoparticles are dispersed in water at three different concentrations, ϕ = 0.15%, 0.48%, and 0.59% (w/v) [g/ml%] and exposed to uniform magnetic fields in the range of H = 0.05–0.42 T. Cryogenic transmission electron microscopy is employed to provide in-situ observations of the field-induced assemblies in such systems. As the magnetic field increases, the Brownian colloids are observed to form randomly distributed chains aligned in the field direction, followed by head-to-tail chain aggregation and then lateral aggregation of chains termed as zippering. By increasing the field in low concentration samples, the number of chains increases, though their length does not change dramatically. Increasing concentration increases the length of the linear particle assemblies in the presence of a fixed external magnetic field. Thickening of the chains due to zippering is observed at relatively high fields. Through a systematic variation of concentration and magnetic field strength, this study shows that both magnetic field strength and change in concentration can strongly influence formation of microstructures even in weak dipolar systems. Additionally, the results of two commonly used support films on electron microscopy grids, continuous carbon and holey carbon films, are compared. Holey carbon film allows us to create local regions of high concentrations that further assist the development of field-induced assemblies. The experimental observations provide a validation of the zippering effect and can be utilized in the development of models for thermophysical properties such as thermal conductivity.

  11. Quantum criticality at the Anderson transition: A typical medium theory perspective

    Science.gov (United States)

    Mahmoudian, Samiyeh; Tang, Shao; Dobrosavljević, Vladimir

    2015-10-01

    We present a complete analytical and numerical solution of the typical medium theory (TMT) for the Anderson metal-insulator transition. This approach self-consistently calculates the typical amplitude of the electronic wave functions, thus representing the conceptually simplest order-parameter theory for the Anderson transition. We identify all possible universality classes for the critical behavior, which can be found within such a mean-field approach. This provides insights into how interaction-induced renormalizations of the disorder potential may produce qualitative modifications of the critical behavior. We also formulate a simplified description of the leading critical behavior, thus obtaining an effective Landau theory for Anderson localization.

  12. Large epitaxial bi-axial strain induces a Mott-like phase transition in VO{sub 2}

    Energy Technology Data Exchange (ETDEWEB)

    Kittiwatanakul, Salinporn [Department of Physics, University of Virginia, Charlottesville, Virginia 22904 (United States); Wolf, Stuart A. [Department of Physics, University of Virginia, Charlottesville, Virginia 22904 (United States); Department of Materials Science and Engineering, University of Virginia, Charlottesville, Virginia 22904 (United States); Lu, Jiwei, E-mail: jl5tk@virginia.edu [Department of Materials Science and Engineering, University of Virginia, Charlottesville, Virginia 22904 (United States)

    2014-08-18

    The metal insulator transition (MIT) in vanadium dioxide (VO{sub 2}) has been an important topic for recent years. It has been generally agreed upon that the mechanism of the MIT in bulk VO{sub 2} is considered to be a collaborative Mott-Peierls transition, however, the effect of strain on the phase transition is much more complicated. In this study, the effect of the large strain on the properties of VO{sub 2} films was investigated. One remarkable result is that highly strained epitaxial VO{sub 2} thin films were rutile in the insulating state as well as in the metallic state. These highly strained VO{sub 2} films underwent an electronic phase transition without the concomitant Peierls transition. Our results also show that a very large tensile strain along the c-axis of rutile VO{sub 2} resulted in a phase transition temperature of ∼433 K, much higher than in any previous report. Our findings elicit that the metal insulator transition in VO{sub 2} can be driven by an electronic transition alone, rather the typical coupled electronic-structural transition.

  13. The giant piezoelectric effect: electric field induced monoclinic phase or piezoelectric distortion of the rhombohedral parent?

    CERN Document Server

    Kisi, E H; Forrester, J S; Howard, C J

    2003-01-01

    Lead zinc niobate-lead titanate (PZN-PT) single crystals show very large piezoelectric strains for electric fields applied along the unit cell edges e.g. [001] sub R. It has been widely reported that this effect is caused by an electric field induced phase transition from rhombohedral (R3m) to monoclinic (Cm or Pm) symmetry in an essentially continuous manner. Group theoretical analysis using the computer program ISOTROPY indicates phase transitions between R3m and Cm (or Pm) must be discontinuous under Landau theory. An analysis of the symmetry of a strained unit cell in R3m and a simple expansion of the piezoelectric strain equation indicate that the piezoelectric distortion due to an electric field along a cell edge in rhombohedral perovskite-based ferroelectrics is intrinsically monoclinic (Cm), even for infinitesimal electric fields. PZN-PT crystals have up to nine times the elastic compliance of other piezoelectric perovskites and it might be expected that the piezoelectric strains are also very large. ...

  14. Magnetic Fields Induced in the Solid Earth and Oceans

    DEFF Research Database (Denmark)

    Kuvshinov, Alexei; Olsen, Nils

    Electromagnetic induction in the Earth's interior is an important contributor to the near-Earth magnetic field. Oceans play a special role in the induction, due to their relatively high conductance of large lateral variability. Electric currents that generate secondary magnetic fields are induced...... ocean circulation. Finally, we will discuss how the results of 3-D predictions can be utilized in geomagnetic field modeling and in a recovery of deep conductivity structures.......Electromagnetic induction in the Earth's interior is an important contributor to the near-Earth magnetic field. Oceans play a special role in the induction, due to their relatively high conductance of large lateral variability. Electric currents that generate secondary magnetic fields are induced...... in the oceans by two different sources: by time varying external magnetic fields, and by motion of the conducting ocean water through the Earth's main magnetic field. Significant progress in the accurate and detailed prediction of magnetic fields induced by these sources has been achieved during the last years...

  15. Benzene at 1 GHz. Magnetic field-induced fine structure

    Science.gov (United States)

    Heist, L. M.; Poon, C.-D.; Samulski, E. T.; Photinos, D. J.; Jokisaari, J.; Vaara, J.; Emsley, J. W.; Mamone, S.; Lelli, M.

    2015-09-01

    The deuterium NMR spectrum of benzene-d6 in a high field spectrometer (1 GHz protons) exhibits a magnetic field-induced deuterium quadrupolar splitting Δν. The magnitude of Δν observed for the central resonance is smaller than that observed for the 13C satellite doublets Δν‧. This difference, Δ(Δν) = Δν‧ - Δν, is due to unresolved fine structure contributions to the respective resonances. We determine the origins of and simulate this difference, and report pulse sequences that exploit the connectivity of the peaks in the 13C and 2H spectra to determine the relative signs of the indirect coupling, JCD, and Δν. The positive sign found for Δν is consonant with the magnetic field biasing of an isolated benzene molecule-the magnetic energy of the aromatic ring is lowest for configurations where the C6 axis is normal to the field. In the neat liquid the magnitude of Δν is decreased by the pair correlations in this prototypical molecular liquid.

  16. A telluric method for natural field induced polarization studies

    Science.gov (United States)

    Zorin, Nikita; Epishkin, Dmitrii; Yakovlev, Andrey

    2016-12-01

    Natural field induced polarization (NFIP) is a branch of low-frequency electromagnetics designed for detection of buried polarizable objects from magnetotelluric (MT) data. The conventional approach to the method deals with normalized MT apparent resistivity. We show that it is more favorable to extract the IP effect from solely electric (telluric) transfer functions instead. For lateral localization of polarizable bodies it is convenient to work with the telluric tensor determinant, which does not depend on the rotation of the receiving electric dipoles. Applicability of the new method was verified in the course of a large-scale field research. The field work was conducted in a well-explored area in East Kazakhstan known for the presence of various IP sources such as graphite, magnetite, and sulfide mineralization. A new multichannel processing approach allowed the determination of the telluric tensor components with very good accuracy. This holds out a hope that in some cases NFIP data may be used not only for detection of polarizable objects, but also for a rough estimation of their spectral IP characteristics.

  17. Complex Electric-Field Induced Phenomena in Ferroelectric/Antiferroelectric Nanowires

    Science.gov (United States)

    Herchig, Ryan Christopher

    -principles-based modeling of electric-field-induced phenomena in ferroelectric/antiferroelectric nanowires in order to address the aforementioned questions. (Abstract shortened by ProQuest.).

  18. Large field-induced irreversibility in Ni-Mn based Heusler shape-memory alloys: A pulsed magnetic field study

    Science.gov (United States)

    Nayak, A. K.; Mejia, C. Salazar; D'Souza, S. W.; Chadov, S.; Skourski, Y.; Felser, C.; Nicklas, M.

    2014-12-01

    We present a pulsed magnetic field study on the magnetic and magnetostriction properties of Ni-Mn-Z (Z =In , Sn, and Sb) based Heusler shape-memory alloys. These materials generally display a field-induced magnetostructural transition that could lead to an irreversible phase transition, when measured near the martensitic transition temperature. Here, we show that independently of the transition temperature, the critical field for the phase transition sensitively depends on the main-group element in the sample. Irrespective of their compositions, all samples display a magnetization of around 2 μB/f .u . in the martensite phase and about 6 μB/f .u . in the cubic austenite phase. Our magnetic and magnetostriction measurements at low temperatures exhibit a partial or complete arrest of the high-field austenite phase below the reverse martensitic transition. This results in a large irreversibility with a hysteresis width as high as 24 T. We introduce a theoretical model to discuss the experimental results.

  19. AlGaN/GaN Metal-Insulator-Semiconductor High Electron-Mobility Transistor Using a NbAlO/Al2O3 Laminated Dielectric by Atomic Laver Deposition

    Institute of Scientific and Technical Information of China (English)

    BI Zhi-Wei; YANG Lin-An; MEI Nan; CHANG Yong-Ming; HAO Yue; FENG Qian; GAO Zhi-Yuan; ZHANG Jin-Cheng; MAO Wei; ZHANG Kai; MA Xiao-Hua; LIU Hong-Xia

    2012-01-01

    We investigate the characteristics of AlGaN/GaN metal-insulator-semiconductor high-electron-mobility transistors (MIS-HEMTs) with a NbAlO/Al2O3 lamination dielectric deposited by atomic layer deposition (ALD) as the gate insulator.A large gate voltage swing (GVS) of 3.96 V and a high breakdown voltage of-150 V for the MIS-HEMT were obtained.We present the gate leakage current mechanisms and analyze the reason for the reduction of the leakage current.Compared with traditional HEMTs,the maximum drain current is improved to 960mA/mm,indicating that NbAlO layers could reduce the surface-related depletion of the channel layer and increase the sheet carrier concentration.In addition,the maximum oscillation frequency of 38.8 GHz shows that the NbAlO high-k dielectric can be considered as a potential gate oxide comparable with other dielectric insulators.%We investigate the characteristics of AlGaN/GaN metal-insulator-semiconductor high-electron-mobility transistors (MIS-HEMTs) with a NbAlO/AI2O3 lamination dielectric deposited by atomic layer deposition (ALD) as the gate insulator. A large gate voltage swing (GVS) of 3.96 V and a high breakdown voltage of -150V for the MIS-HEMT were obtained. We present the gate leakage current mechanisms and analyze the reason for the reduction of the leakage current. Compared with traditional HEMTs, the maximum drain current is improved to 960mA/mm, indicating that NbAlO layers could reduce the surface-related depletion of the channel layer and increase the sheet carrier concentration. In addition, the maximum oscillation frequency of 38.8 GHz shows that the NbAlO high-k dielectric can be considered as a potential gate oxide comparable with other dielectric insulators.

  20. Domain walls in Fe(001) bicrystals-thickness dependence and field-induced transitions

    Energy Technology Data Exchange (ETDEWEB)

    Hanson, M. [Department of Applied physics, Chalmers University of Technology, SE-412 96 Goeteborg (Sweden)]. E-mail: maj.hanson@fy.chalmers.se; Brucas, R. [Department of Applied physics, Chalmers University of Technology, SE-412 96 Goeteborg (Sweden)

    2007-03-15

    Magnetic domain walls (DW's) formed at the grain boundary (GB) of epitaxial bicrystal Fe(001) films, thickness t=50 and 70nm, were studied by magnetic force microscopy. The 'as-grown' samples displayed DW's with different magnetic contrast profiles yielding a single peak for t=50nm and a double peak with a change of sign at the centre of the wall for t=70nm. For t=50nm the wall is characterised as an asymmetric Bloch wall. The double peak of the 70nm thick film transformed into a single peak characteristic for a charged wall, when a field of 30mT was applied along the GB. At remanence this domain wall relaxed to a regular Bloch wall divided into segments of alternating signs.

  1. Optical probing of the metal-to-insulator transition in a two-dimensional high-mobility electron gas

    Energy Technology Data Exchange (ETDEWEB)

    Dionigi, F; Rossella, F; Bellani, V [Dipartimento di Fisica ' A Volta' and CNISM, Universita degli Studi di Pavia, 27100 Pavia (Italy); Amado, M [GISC and Departamento de Fisica de Materiales, Universidad Complutense, 28040 Madrid (Spain); Diez, E [Laboratorio de Bajas Temperaturas, Universidad de Salamanca, 37008 Salamanca (Spain); Kowalik, K [Laboratoire National des Champs Magnetiques Intenses, CNRS, 38042 Grenoble (France); Biasiol, G [Istituto Officina dei Materiali CNR, Laboratorio TASC, 34149 Trieste (Italy); Sorba, L, E-mail: vittorio.bellani@unipv.it [NEST, Istituto Nanoscienze-CNR and Scuola Normale Superiore, 56126 Pisa (Italy)

    2011-06-15

    We study the quantum Hall liquid and the metal-insulator transition in a high-mobility two-dimensional electron gas, by means of photoluminescence and magnetotransport measurements. In the integer and fractional regime at {nu}>1/3, by analyzing the emission energy dispersion we probe the magneto-Coulomb screening and the hidden symmetry of the electron liquid. In the fractional regime above {nu}=1/3, the system undergoes metal-to-insulator transition, and in the insulating phase the dispersion becomes linear with evidence of an increased renormalized mass.

  2. Field-induced quantum critical route to a Fermi liquid in high-temperature superconductors.

    Science.gov (United States)

    Shibauchi, Takasada; Krusin-Elbaum, Lia; Hasegawa, Masashi; Kasahara, Yuichi; Okazaki, Ryuji; Matsuda, Yuji

    2008-05-20

    In high-transition-temperature (T(c)) superconductivity, charge doping is a natural tuning parameter that takes copper oxides from the antiferromagnet to the superconducting region. In the metallic state above T(c), the standard Landau's Fermi-liquid theory of metals as typified by the temperature squared (T(2)) dependence of resistivity appears to break down. Whether the origin of the non-Fermi-liquid behavior is related to physics specific to the cuprates is a fundamental question still under debate. We uncover a transformation from the non-Fermi-liquid state to a standard Fermi-liquid state driven not by doping but by magnetic field in the overdoped high-T(c) superconductor Tl(2)Ba(2)CuO(6+x). From the c-axis resistivity measured up to 45 T, we show that the Fermi-liquid features appear above a sufficiently high field that decreases linearly with temperature and lands at a quantum critical point near the superconductivity's upper critical field-with the Fermi-liquid coefficient of the T(2) dependence showing a power-law diverging behavior on the approach to the critical point. This field-induced quantum criticality bears a striking resemblance to that in quasi-two-dimensional heavy-Fermion superconductors, suggesting a common underlying spin-related physics in these superconductors with strong electron correlations.

  3. Large field-induced-strain at high temperature in ternary ferroelectric crystals

    Science.gov (United States)

    Wang, Yaojin; Chen, Lijun; Yuan, Guoliang; Luo, Haosu; Li, Jiefang; Viehland, D.

    2016-10-01

    The new generation of ternary Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 ferroelectric single crystals have potential applications in high power devices due to their surperior operational stability relative to the binary system. In this work, a reversible, large electric field induced strain of over 0.9% at room temperature, and in particular over 0.6% above 380 K was obtained. The polarization rotation path and the phase transition sequence of different compositions in these ternary systems have been determined with increasing electric field applied along [001] direction based on x-ray diffraction data. Thereafter, composition dependence of field-temperature phase diagrams were constructed, which provide compositional and thermal prospectus for the electromechanical properties. It was found the structural origin of the large stain, especially at higher temperature is the lattice parameters modulated by dual independent variables in composition of these ternary solid solution crystals.

  4. Enhanced leakage current behavior of Sr{sub 2}Ta{sub 2}O{sub 7-x}/SrTiO{sub 3} bilayer dielectrics for metal-insulator-metal capacitors

    Energy Technology Data Exchange (ETDEWEB)

    Kaynak, C. Baristiran, E-mail: baristiran@ihp-microelectronics.com [IHP Im Technologiepark 25, 15236 Frankfurt Oder (Germany); Lukosius, M.; Costina, I. [IHP Im Technologiepark 25, 15236 Frankfurt Oder (Germany); Tillack, B. [IHP Im Technologiepark 25, 15236 Frankfurt Oder (Germany); Technische Universitaet Berlin, HFT4, Einsteinufer 25, 10587, Berlin (Germany); Wenger, Ch. [IHP Im Technologiepark 25, 15236 Frankfurt Oder (Germany); Ruhl, G. [Infineon Technologies AG, Wernerwerkstr. 2, 93049 Regensburg (Germany); Blomberg, T. [ASM Microchemistry Ltd., Vaeinoe Auerin katu 12 A, 00560 Helsinki (Finland)

    2011-06-30

    Metal-Insulator-Metal (MIM) capacitors are one of the most essential components of radio frequency devices and analog/mixed-signal integrated circuits. In order to obtain high capacitance densities in MIM devices, high-k materials have been considered to be promising candidates to replace the traditional insulators. The challenging point is that the dielectric material must demonstrate high capacitance density values with low leakage current densities. In this work, SrTiO{sub 3} based MIM capacitors have been investigated and the electrical performance of the devices have been optimized by using bilayered systems of Sr{sub 2}Ta{sub 2}O{sub 7-x}/SrTiO{sub 3} with different thicknesses of Sr{sub 2}Ta{sub 2}O{sub 7-x}. Sputtering X-Ray photoelectron spectroscopy (XPS) measurements have been applied to investigate the interfaces between the thin film constituents of the MIM stacks. The optimized bilayered system provides a leakage current density of 8*10{sup -8} A/cm{sup 2} at 2 V (bottom electrode injection) and a high capacitance density of 13 fF/{mu}m{sup 2}.

  5. Effect of AlN growth temperature on trap densities of in-situ metal-organic chemical vapor deposition grown AlN/AlGaN/GaN metal-insulator-semiconductor heterostructure field-effect transistors

    Directory of Open Access Journals (Sweden)

    Joseph J. Freedsman

    2012-06-01

    Full Text Available The trapping properties of in-situ metal-organic chemical vapor deposition (MOCVD grown AlN/AlGaN/GaN metal-insulator-semiconductor heterostructure field-effect transistors (MIS-HFETs with AlN layers grown at 600 and 700 °C has been quantitatively analyzed by frequency dependent parallel conductance technique. Both the devices exhibited two kinds of traps densities, due to AlN (DT-AlN and AlGaN layers (DT-AlGaN respectively. The MIS-HFET grown at 600 °C showed a minimum DT-AlN and DT-AlGaN of 1.1 x 1011 and 1.2 x 1010 cm-2eV-1 at energy levels (ET -0.47 and -0.36 eV. Further, the gate-lag measurements on these devices revealed less degradation ∼ ≤ 5% in drain current density (Ids-max. Meanwhile, MIS-HFET grown at 700 °C had more degradation in Ids-max ∼26 %, due to high DT-AlN and DT-AlGaN of 3.4 x 1012 and 5 x 1011 cm-2eV-1 positioned around similar ET. The results shows MIS-HFET grown at 600 °C had better device characteristics with trap densities one order of magnitude lower than MIS-HFET grown at 700 °C.

  6. Possible Kondo physics near a metal-insulator crossover in the a-site ordered perovskite CaCu3Ir4O12.

    Science.gov (United States)

    Cheng, J-G; Zhou, J-S; Yang, Y-F; Zhou, H D; Matsubayashi, K; Uwatoko, Y; MacDonald, A; Goodenough, J B

    2013-10-25

    The A-site ordered perovskite (AA(3)')B(4)O(12) can accommodate transition metals on both A' and B sites in the crystal structure. Because of this structural feature, it is possible to have narrow-band electrons interacting with broadband electrons from different sublattices. Here we report a new A-site ordered perovskite (CaCu(3))Ir(4)O(12) synthesized under high pressure. The coupling between localized spins on Cu(2+) and itinerant electrons from the Ir-O sublattice makes Kondo-like physics take place at a temperature as high as 80 K. Results from the local density approximation calculation have confirmed the relevant band structure. The magnetization anomaly found at 80 K can be well rationalized by the two-fluid model.

  7. Influence of Doping on the Mott Metal—Insulator Transition in Infinite Dimensions

    Institute of Scientific and Technical Information of China (English)

    TONGNing-Hua

    2002-01-01

    We have studied the effect of hole-doping on the established scenerio of the first-order Mott metal-insulator transition (MIT) at half-filling using dynamical mean-field theory and exact diagonalization technique.The mott insulator state is changed into metallic state immediately as holes are doped into the system.The latter is expected to be Fermi liquid.The previously found unanalytical structure of MIT no longer exists for doping as small as 2 percent.We compare our results with that obtained from Gutzwiller approximation.

  8. Transformation and Field-Induced Strains in as-Cast Ni-Mn-Ga Alloy

    Institute of Scientific and Technical Information of China (English)

    ZHAO Wei-ren; LI Jian-liang; QI Yan; ZHANG Yang-huan; WANG Xin-lin; YU Yuan-jun

    2004-01-01

    The characteristics of the strains induced by transformation and magnetic field in as-cast Ni-Mn-Ga alloy were systematically investigated. It is found that internal stress and texture introduced during casting bring the anisotropy of temperature-induced strains. However, no anisotropy of field-induced strains is induced, and the internal stress and the texture modulate only the temperature dependence of field-induced strains. Large retardance of field-induced strains was observed, which indicates the rearrangement of martensitic variants as a competition process between the stress energy and Zeeman energy. The non-continuous field dependence of strain indicates the unstable microstructure during martensitic transformation.

  9. Dynamic transition in supercritical iron.

    Science.gov (United States)

    Fomin, Yu D; Ryzhov, V N; Tsiok, E N; Brazhkin, V V; Trachenko, K

    2014-11-26

    Recent advance in understanding the supercritical state posits the existence of a new line above the critical point separating two physically distinct states of matter: rigid liquid and non-rigid gas-like fluid. The location of this line, the Frenkel line, remains unknown for important real systems. Here, we map the Frenkel line on the phase diagram of supercritical iron using molecular dynamics simulations. On the basis of our data, we propose a general recipe to locate the Frenkel line for any system, the recipe that importantly does not involve system-specific detailed calculations and relies on the knowledge of the melting line only. We further discuss the relationship between the Frenkel line and the metal-insulator transition in supercritical liquid metals. Our results enable predicting the state of supercritical iron in several conditions of interest. In particular, we predict that liquid iron in the Jupiter core is in the "rigid liquid" state and is highly conducting. We finally analyse the evolution of iron conductivity in the core of smaller planets such as Earth and Venus as well as exoplanets: as planets cool off, the supercritical core undergoes the transition to the rigid-liquid conducting state at the Frenkel line.

  10. Phase stability and magnetic-field-induced martensitic transformation in Mn-rich NiMnSn alloys

    Directory of Open Access Journals (Sweden)

    Q. Tao

    2012-12-01

    Full Text Available A series of Ni50-xMn41+xSn9 (x = 0–19 alloys from Ni-rich to Mn-rich composition were prepared, and the composition dependence of phase transitions and magnetic properties were investigated. No γ-phase can be observed until x = 17. Martensitic transformation from ferromagnetic austenite to weak-magnetic or ferromagnetic martensite was observed in alloys with Mn content between 52 and 58, and magnetic-field-induced transformation was confirmed. A large magnetization change of 44 Am2/kg across the martensitic transformation is observed in Ni37Mn54Sn9. Our results indicate that Mn-rich Ni-Mn-Sn alloys show promise as metamagnetic shape memory alloys.

  11. Voltage-dependent capacitance behavior and underlying mechanisms in metal-insulator-metal capacitors with Al2O3-ZrO2-SiO2 nano-laminates

    Science.gov (United States)

    Zhu, Bao; Liu, Wen-Jun; Wei, Lei; Ding, Shi-Jin

    2016-04-01

    Nano-laminates consisting of high-permittivity dielectrics and SiO2 have been extensively studied for radio frequency metal-insulator-metal (MIM) capacitors because of their superior voltage linearity and low leakage current. However, there are no reports on the capacitance-voltage (C-V) characteristics at a high sweep voltage range. In this work, an interesting variation in the voltage-dependent capacitance that forms a ‘ω’-like shape is demonstrated for the MIM capacitors with Al2O3/ZrO2/SiO2 nano-laminates. As the thickness ratio of the SiO2 film to the total insulator increases to around 0.15, the C-V curve changes from an upward parabolic shape to a ‘ω’ shape. This can be explained based on the competition between the orientation polarization from SiO2 and the electrode polarization from Al2O3 and ZrO2. When the SiO2 film is very thin, the electrode polarization dominates in the MIM capacitor, generating a positive curvature C-V curve. When the thickness of SiO2 is increased, the orientation polarization is enhanced and thus both polarizations are operating in the MIM capacitors. This leads to the appearance of a multiple domain C-V curve containing positive and negative curvatures. Therefore, good consistency between the experimental results and the theoretical simulations is demonstrated. Such voltage-dependent capacitance behavior is not determined by the stack structure of the insulator, measurement frequency and oscillator voltage, but by the thickness ratio of the SiO2 film to the whole insulator. These findings are helpful to engineer MIM capacitors with good voltage linearity.

  12. Detecting phase transitions and crossovers in Hubbard models using the fidelity susceptibility

    Science.gov (United States)

    Huang, Li; Wang, Yilin; Wang, Lei; Werner, Philipp

    2016-12-01

    A generalized version of the fidelity susceptibility of single-band and multiorbital Hubbard models is systematically studied using single-site dynamical mean-field theory in combination with a hybridization expansion continuous-time quantum Monte Carlo impurity solver. We find that the fidelity susceptibility is extremely sensitive to changes in the state of the system. It can be used as a numerically inexpensive tool to detect and characterize a broad range of phase transitions and crossovers in Hubbard models, including (orbital-selective) Mott metal-insulator transitions, magnetic phase transitions, high-spin to low-spin transitions, Fermi-liquid to non-Fermi-liquid crossovers, and spin-freezing crossovers.

  13. The transition to the metallic state in low density hydrogen

    Energy Technology Data Exchange (ETDEWEB)

    McMinis, Jeremy; Morales, Miguel A. [Lawrence Livermore National Laboratory, Livermore, California 94550 (United States); Ceperley, David M. [Department of Physics, University of Illinois, Urbana, Illinois 61801 (United States); Kim, Jeongnim [Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States)

    2015-11-21

    Solid atomic hydrogen is one of the simplest systems to undergo a metal-insulator transition. Near the transition, the electronic degrees of freedom become strongly correlated and their description provides a difficult challenge for theoretical methods. As a result, the order and density of the phase transition are still subject to debate. In this work, we use diffusion quantum Monte Carlo to benchmark the transition between paramagnetic and anti-ferromagnetic body centered cubic atomic hydrogen in its ground state. We locate the density of the transition by computing the equation of state for these two phases and identify the phase transition order by computing the band gap near the phase transition. These benchmark results show that the phase transition is continuous and occurs at a Wigner-Seitz radius of r{sub s} = 2.27(3) a{sub 0}. We compare our results to previously reported density functional theory, Hedin’s GW approximation, and dynamical mean field theory results.

  14. Investigating compositional effects of atomic layer deposition ternary dielectric Ti-Al-O on metal-insulator-semiconductor heterojunction capacitor structure for gate insulation of InAlN/GaN and AlGaN/GaN

    Energy Technology Data Exchange (ETDEWEB)

    Colon, Albert; Stan, Liliana; Divan, Ralu; Shi, Junxia

    2016-11-01

    Gate insulation/surface passivation in AlGaN/GaN and InAlN/GaN heterojunction field-effect transistors is a major concern for passivation of surface traps and reduction of gate leakage current. However, finding the most appropriate gate dielectric materials is challenging and often involves a compromise of the required properties such as dielectric constant, conduction/valence band-offsets, or thermal stability. Creating a ternary compound such as Ti-Al-O and tailoring its composition may result in a reasonably good gate material in terms of the said properties. To date, there is limited knowledge of the performance of ternary dielectric compounds on AlGaN/GaN and even less on InAlN/GaN. To approach this problem, the authors fabricated metal-insulator-semiconductor heterojunction (MISH) capacitors with ternary dielectrics Ti-Al-O of various compositions, deposited by atomic layer deposition (ALD). The film deposition was achieved by alternating cycles of TiO2 and Al2O3 using different ratios of ALD cycles. TiO2 was also deposited as a reference sample. The electrical characterization of the MISH capacitors shows an overall better performance of ternary compounds compared to the pure TiO2. The gate leakage current density decreases with increasing Al content, being similar to 2-3 orders of magnitude lower for a TiO2:Al2O3 cycle ratio of 2:1. Although the dielectric constant has the highest value of 79 for TiO2 and decreases with increasing the number of Al2O3 cycles, it is maintaining a relatively high value compared to an Al2O3 film. Capacitance voltage sweeps were also measured in order to characterize the interface trap density. A decreasing trend in the interface trap density was found while increasing Al content in the film. In conclusion, our study reveals that the desired high-kappa properties of TiO2 can be adequately maintained while improving other insulator performance factors. The ternary compounds may be an excellent choice as a gate material for both

  15. Dynamics of glass-forming liquids. XIX. Rise and decay of field induced anisotropy in the non-linear regime.

    Science.gov (United States)

    Young-Gonzales, Amanda R; Samanta, Subarna; Richert, Ranko

    2015-09-14

    For glycerol and three monohydroxy alcohols, we have measured the non-linear dielectric effects resulting from the application and removal of a high dc bias electric field. The field effects are detected by virtue of a small amplitude harmonic field, from which time resolved changes in the dielectric loss are derived. The changes in permittivity are dominated by modifications of the time constants (rather than amplitudes) which display two contributions: a heating-like decrease of relaxation times that originates from the time dependent field when the bias is switched on and off and a slowing down of the dynamics resulting from the field induced reduction of configurational entropy. As observed for the electro-optical Kerr effect, the rise of the entropy change is slower than its decay, a feature that we rationalize on the basis of the quadratic dependence of the entropy change on polarization. For glycerol, the observed steady state level of the field induced shift of the glass transition temperature (+84 mK) matches the expectation based on the entropy change and its impact on dynamics via the Adam-Gibbs relation (+88 mK). For the alcohols, these non-linear effects rise and decay on the time scales of the prominent dielectric Debye process, underscoring the relation of these features to polarization anisotropy, opposed to mechanical or enthalpy relaxation which are orders of magnitude faster in these systems. A model is discussed which captures the observed magnitudes as well as time dependences in a near quantitative fashion. It is demonstrated that the high bias field modifies the response of polarization to the ac field, including a temporary change in the low field susceptibility.

  16. Slater to Mott Crossover in the Metal to Insulator Transition of Nd2Ir2O7

    Science.gov (United States)

    Nakayama, M.; Kondo, Takeshi; Tian, Z.; Ishikawa, J. J.; Halim, M.; Bareille, C.; Malaeb, W.; Kuroda, K.; Tomita, T.; Ideta, S.; Tanaka, K.; Matsunami, M.; Kimura, S.; Inami, N.; Ono, K.; Kumigashira, H.; Balents, L.; Nakatsuji, S.; Shin, S.

    2016-07-01

    We present an angle-resolved photoemission study of the electronic structure of the three-dimensional pyrochlore iridate Nd2Ir2O7 through its magnetic metal-insulator transition. Our data reveal that metallic Nd2Ir2O7 has a quadratic band, touching the Fermi level at the Γ point, similar to that of Pr2Ir2O7 . The Fermi node state is, therefore, a common feature of the metallic phase of the pyrochlore iridates. Upon cooling below the transition temperature, this compound exhibits a gap opening with an energy shift of quasiparticle peaks like a band gap insulator. The quasiparticle peaks are strongly suppressed, however, with further decrease of temperature, and eventually vanish at the lowest temperature, leaving a nondispersive flat band lacking long-lived electrons. We thereby identify a remarkable crossover from Slater to Mott insulators with decreasing temperature. These observations explain the puzzling absence of Weyl points in this material, despite its proximity to the zero temperature metal-insulator transition.

  17. Electric-field-induced second harmonic generation in GaAs

    Energy Technology Data Exchange (ETDEWEB)

    Lafrentz, Marco; Brunne, David; Kaminski, Benjamin; Bayer, Manfred [Experimentelle Physik 2, Technische Universitaet Dortmund, D-44221 Dortmund (Germany); Yakovlev, Dmitri R. [Experimentelle Physik 2, Technische Universitaet Dortmund, D-44221 Dortmund (Germany); Ioffe Physico-Technical Institute, Russian Academy of Sciences, 194021 St. Petersburg (Russian Federation); Pavlov, Victor V.; Pisarev, Roman V. [Ioffe Physico-Technical Institute, Russian Academy of Sciences, 194021 St. Petersburg (Russian Federation)

    2011-07-01

    We report on electric-field-induced second-harmonic generation (SHG) in the GaAs semiconductor in the vicinity of the band gap. The light has been send along 001-crystallographic direction. In this geometry SHG is forbidden in electric-dipole approximation. In applied electric field the SHG signal arises due to field-induced symmetry breaking causing new optical nonlinearities. Electric-field and temperature investigations assign the strong signal at E(2{omega})=1.517 eV for T=2 K to excitonic resonance. This phenomenon is a supplementary tool for detailed investigation of complex susceptibilities we have reported on in the past.

  18. Electric-field-induced soft-mode hardening in SrTiO3 films

    Science.gov (United States)

    Akimov; Sirenko; Clark; Hao; Xi

    2000-05-15

    We have studied electric-field-induced Raman scattering in SrTiO3 thin films using an indium-tin-oxide/SrTiO3/SrRuO3 structure grown by pulsed laser deposition. The soft mode polarized along the field becomes Raman active. Experimental data for electric-field-induced hardening of the soft modes and the tuning of the static dielectric constant are in agreement described by the Lyddane-Sachs-Teller formalism. The markedly different behavior of the soft modes in thin films from that in the bulk is explained by the existence of local polar regions.

  19. Field induced rotational viscosity of ferrofluid: effect of capillary size and magnetic field direction.

    Science.gov (United States)

    Andhariya, Nidhi; Chudasama, Bhupendra; Patel, Rajesh; Upadhyay, R V; Mehta, R V

    2008-07-01

    In the present investigation we report the effect of capillary diameter and the direction of applied magnetic field on the rotational viscosity of water and kerosene based ferrofluids. We found that changes in the field induced rotational viscosity are larger in the case of water based magnetic fluid than that of kerosene based fluid. The field induced rotational viscosity is found to be inversely proportional to the capillary diameter and it falls exponentially as a function of the angle between the direction of field and vorticity of flow. Magnetophoretic mobility and hydrodynamic volume fraction of nanomagnetic particles are determined for above cases.

  20. YbNiAl{sub 2}: A new Yb-based antiferromagnet with a field-induced ferromagnetic order

    Energy Technology Data Exchange (ETDEWEB)

    Rojas, D.P., E-mail: rojasd@unican.e [Departamento CITIMAC, Av de los Castros S/N, Santander 39005 (Spain); Rodriguez Fernandez, J.; Espeso, J.I.; Gomez Sal, J.C. [Departamento CITIMAC, Av de los Castros S/N, Santander 39005 (Spain)

    2009-10-15

    We report measurements on the thermal and magnetic properties in the temperature range 2-300 K for the YbNiAl{sub 2} compound which crystallizes in the orthorhombic MgCuAl{sub 2}-type structure (space group Cmcm). At zero magnetic field, AC-magnetic susceptibility data show a peak in the real component consistent with an antiferromagnetic order below T{sub N}=4.8K. A field-induced ferromagnetic order is observed from the zero field cooled and field cooled curves of DC-magnetic susceptibility at different magnetic fields with a transition to a ferromagnetic state between 9 and 10 kOe. It is further confirmed by the isothermal magnetization curves as a function of the magnetic field at several temperatures, showing two metamagnetic transitions at H{sub 1}=8kOe and H{sub 2}=9.3kOe. The results are compared to those reported for other Yb-Ni-Al compounds.

  1. Bleaching versus poling: Comparison of electric field induced phenomena in glasses and glass-metal nanocomposites

    Science.gov (United States)

    Lipovskii, A. A.; Melehin, V. G.; Petrov, M. I.; Svirko, Yu. P.; Zhurikhina, V. V.

    2011-01-01

    By examining the electric field induced processes in glasses and glass-metal nanocomposites (GMN) we propose mechanism of the electric field assisted dissolution (EFAD) of metal nanoparticles in glass. We show that in both glass poling and EFAD processes, the strong (up to 1 V/nm) local electric field in the subanodic region is due to the presence of "slow" hydrogen ions bonded to nonbridging oxygen atoms in glass matrix. However, the origin of these hydrogen ions in glass and GMN is different. Specifically, when we apply the electric field to a virgin glass, the enrichment of the glass with hydrogen species takes place in the course of the poling. In GMN, the hydrogen ions have been incorporated into the glass matrix during metal nanoparticles formation via reduction in a metal by hydrogen, i.e., before the electric field was applied. The EFAD of metal nanoparticles resembles the electric field stimulated diffusion of metal film in glass (the important difference however is that in GMN, there is no direct contact of dissolving metal entity with anodic electrode). This similarity makes it possible to estimate the energy of thermal activated transition of silver atoms from a nanoparticle to glass matrix as ˜1.3 eV. Electroneutrality of the GMN requires emission of electrons from nanoparticles. Photoconductivity spectra of soda-lime glasses and the results of numerical calculations of band structure of fused silica, sodium disilicate and sodium-calcium-silicate glass enable us to evaluate the bandgap and the position of electron mobility edge in soda-lime glass. The evaluated values are ˜6 eV and ˜1.2 eV below vacuum level, respectively. The bent of the glass band structure in strong electric field permits a direct tunneling of Fermi electrons from silver nanoparticle (4.6 eV below the vacuum level) to the glass conductivity band. Evaluated in accordance with the Fowler-Nordheim equation the magnitude of electric field necessary to establish comparable electron

  2. Enhanced superconductivity and superconductor to insulator transition in nano-crystalline molybdenum thin films

    Science.gov (United States)

    Sharma, Shilpam; Amaladass, E. P.; Sharma, Neha; Harimohan, V.; Amirthapandian, S.; Mani, Awadhesh

    2017-06-01

    Disorder driven superconductor to insulator transition via intermediate metallic regime is reported in nano-crystalline thin films of molybdenum. The nano-structured thin films have been deposited at room temperature using DC magnetron sputtering at different argon pressures. The grain size has been tuned using deposition pressure as the sole control parameter. A variation of particle sizes, room temperature resistivity and superconducting transition has been studied as a function of deposition pressure. The nano-crystalline molybdenum thin films are found to have large carrier concentration but very low mobility and electronic mean free path. Hall and conductivity measurements have been used to understand the effect of disorder on the carrier density and mobilities. Ioffe-Regel parameter is shown to correlate with the continuous metal-insulator transition in our samples.

  3. On the nature of the Mott transition in multiorbital systems

    Science.gov (United States)

    Facio, Jorge I.; Vildosola, V.; García, D. J.; Cornaglia, Pablo S.

    2017-02-01

    We analyze the nature of a Mott metal-insulator transition in multiorbital systems using dynamical mean-field theory. The auxiliary multiorbital quantum impurity problem is solved using continuous-time quantum Monte Carlo and the rotationally invariant slave-boson (RISB) mean-field approximation. We focus our analysis on the Kanamori Hamiltonian and find that there are two markedly different regimes determined by the nature of the lowest-energy excitations of the atomic Hamiltonian. The RISB results at T →0 suggest the following rule of thumb for the order of the transition at zero temperature: a second-order transition is to be expected if the lowest-lying excitations of the atomic Hamiltonian are charge excitations, while the transition tends to be first order if the lowest-lying excitations are in the same charge sector as the atomic ground state. At finite temperatures, the transition is first order and its strength, as measured, e.g., by the jump in the quasiparticle weight at the transition, is stronger in the parameter regime where the RISB method predicts a first-order transition at zero temperature. Interestingly, these results seem to apply to a wide variety of models and parameter regimes.

  4. Directed magnetic field induced assembly of high magnetic moment cobalt nanowires

    DEFF Research Database (Denmark)

    Srivastava, Akhilesh Kumar; Madhavi, S.; Ramanujan, R.V.

    2010-01-01

    A directed magnetic field induced assembly technique was employed to align two phase (h.c.p. + f.c.c.) cobalt nanoparticles in a mechanically robust long wire morphology. Co nanoparticles with an average size of 4.3 nm and saturation magnetization comparable to bulk cobalt were synthesized...

  5. The influence of sulcus width on simulated electric fields induced by transcranial magnetic stimulation

    NARCIS (Netherlands)

    Janssen, A.M.; Rampersad, S.M.; Lucka, F.; Lanfer, B.; Lew, S.; Aydin, U.; Wolters, C.H.; Stegeman, D.F.; Oostendorp, T.F.

    2013-01-01

    Volume conduction models can help in acquiring knowledge about the distribution of the electric field induced by transcranial magnetic stimulation. One aspect of a detailed model is an accurate description of the cortical surface geometry. Since its estimation is difficult, it is important to know h

  6. Ytterbium can relax slowly too: a field-induced Yb2 single-molecule magnet.

    Science.gov (United States)

    Lin, Po-Heng; Sun, Wen-Bin; Tian, Yong-Mei; Yan, Peng-Fei; Ungur, Liviu; Chibotaru, Liviu F; Murugesu, Muralee

    2012-10-28

    An unusual dinuclear Yb(2) complex isolated using a mixed ligand strategy leads to field-induced SMM behaviour. Low magnetic axiality and a large tunnelling gap lead to significant quantum tunnelling of the magnetisation, which was reduced under an applied static optimum field of 1600 Oe.

  7. Spatiotemporal structure of intracranial electric fields induced by transcranial electric stimulation in humans and nonhuman primates

    DEFF Research Database (Denmark)

    Opitz, Alexander; Falchier, Arnaud; Yan, Chao-Gan

    2016-01-01

    Transcranial electric stimulation (TES) is an emerging technique, developed to non-invasively modulate brain function. However, the spatiotemporal distribution of the intracranial electric fields induced by TES remains poorly understood. In particular, it is unclear how much current actually reac...

  8. Self-consistent electric field-induced dipole interaction of colloidal spheres, cubes, rods, and dumbbells

    NARCIS (Netherlands)

    Kwaadgras, Bas W.; Van Roij, René; Dijkstra, Marjolein

    2014-01-01

    When calculating the interaction between electric field-induced dipoles, the dipole moments are often taken to be equal to their polarizability multiplied by the external electric field. However, this approach is not exact, since it does not take into account the fact that particles with a dipole mo

  9. Strong-field-induced attosecond dynamics in SiO2

    Directory of Open Access Journals (Sweden)

    Kienberger R.

    2013-03-01

    Full Text Available Striking field-induced changes in the absorption near the Si L-edge of SiO2 exposed to a near-infrared laser field of several V/Å delivered by a few-cycle pulse are observed with sub-100 attosecond extreme ultraviolet pulses by means of attosecond transient absorption.

  10. Role of Entropy and Structural Parameters in the Spin State Transition of LaCoO3

    Science.gov (United States)

    Chakrabarti, Bismayan; Birol, Turan; Haule, Kristjan

    The spin state transition in LaCoO3 has eluded description for decades despite concerted theoretical and experimental effort. In this study, we approach this problem using fully charge consistent Density Functional Theory + Dynamical Mean Field Theory (DFT+DMFT). We show, from first principles, that LaCoO3 cannot be described by a single, pure spin state at any temperature, but instead shows a gradual change in the population of higher spin multiples as temperature is increased. We explicitly elucidate the critical role of the lattice expansion and oxygen octahedral rotations in the spin state transition. We also show that the spin state transition and the metal-insulator transition in the compound occur at different temperatures. In addition, our results shed light on the importance of electronic entropy, which has so far been ignored in all first principles studies of this material.

  11. Magnetic field-induced modification of selection rules for Rb D 2 line monitored by selective reflection from a vapor nanocell

    Science.gov (United States)

    Klinger, Emmanuel; Sargsyan, Armen; Tonoyan, Ara; Hakhumyan, Grant; Papoyan, Aram; Leroy, Claude; Sarkisyan, David

    2017-08-01

    Magnetic field-induced giant modification of the probabilities of five transitions of 5 S 1 / 2, F g = 2 → 5 P 3 / 2, F e = 4 of 85Rb and three transitions of 5 S 1 / 2, F g = 1 → 5 P 3 / 2, F e = 3 of 87Rb forbidden by selection rules for zero magnetic field has been observed experimentally and described theoretically for the first time. For the case of excitation with circularly-polarized ( σ +) laser radiation, the probability of F g = 2, m F = - 2 → F e = 4, m F = - 1 transition becomes the largest among the seventeen transitions of 85Rb F g = 2 → F e = 1,2,3,4 group, and the probability of F g = 1, m F = - 1 → F e = 3, m F = 0 transition becomes the largest among the nine transitions of 87Rb F g = 1 → F e = 0,1,2,3 group, in a wide range of magnetic field 200-1000 G. Complete frequency separation of individual Zeeman components was obtained by implementation of derivative selective reflection technique with a 300 nm-thick nanocell filled with Rb, allowing formation of narrow optical resonances. Possible applications are addressed. The theoretical model is well consistent with the experimental results.

  12. EUO-Based Multifunctional Heterostructures

    Science.gov (United States)

    2015-06-06

    magnetic exchange interaction.20 In collaboration with Jochen Mannhart’s group we found a way to extend the large metal- to- insulator transition (MIT...conduction band,24,25 allowing for the temperature and magnetic field induced switching between non-linear and linear current-voltage characteristics...magnetoresistance and the metal- insulator transition resistance ratios of doped EuO by interfacing this semiconductor with niobium; the observed effect is

  13. NMR investigation of field-induced magnetic order in barium manganese oxide

    Science.gov (United States)

    Suh, Steve

    As early as 1956, Matsubara and Matsuda found an exact correspondence between a lattice gas model and a quantum antiferromagnet model[1]. They paved the way for the language of integer spin boson particles to be used interchangeably with quantum magnetic insulator systems in a general manner. For example, an analogy of density of bosons is found in magnetization, and analogy of chemical potential is found in external field. Just as there exist corresponding parameters between these two seemingly unrelated systems, quantum magnets can also exhibit consequences of Boson particle systems. In particular, spin-ordering transition in quantum magnets can be interpreted as Bose-Einstein condensate (BEC) transition in Boson particle framework. Direct observation of BEC in Boson particles has been realized in 4He's superfluid transition and in dilute atomic gas clouds cooled to very low temperatures[2]. In this thesis, we try to realize and analyze BEC transition through field-induced spin-ordering transition in the S = 1 antiferromagnetic dimer system, Ba3Mn2O8. We perform NMR measurements with 135,137Ba nucleus as a local probe. Although S = 1 spin properties of Ba 3Mn2O8 come from electronic spins on Mn atoms, hyperfine coupling between Mn electronic spins and Ba nuclear spins allow us to infer Mn electrons' spin information. Since there are 2 inequivalent Ba sites, Ba(1) and Ba(2), in Ba3Mn2O8, we essentially have two probes that provide a detailed picture of structure and nature of magnetism in this material. There are many antiferromagnetic BEC candidates, but there is a significant advantage of studying Ba3Mn 2O8. Unlike the other popular antiferromagnetic BEC candidates such as TlCuCl3[3] or BaCuSi2O6[4], we find no evidence of lattice deformation in Ba3Mn2O8 . This allows us an unprecedented clean look at magnetic properties. Aside from the aforementioned simple technical advantage, there are new physics that we can learn from Ba3Mn2O 8. The geometric frustration of

  14. Interaction between extended and localized electronic states in the region of the metal to insulator transition in semiconductor alloys

    Energy Technology Data Exchange (ETDEWEB)

    Teubert, Joerg

    2008-07-01

    The first part of this work addresses the influence of those isovalent localized states on the electronic properties of (B,Ga,In)As. Most valuable were the measurements under hydrostatic pressure that revealed a pressure induced metal-insulator transition. One of the main ideas in this context is the trapping of carriers in localized B-related cluster states that appear in the bandgap at high pressure. The key conclusion that can be drawn from the experimental results is that boron atoms seem to have the character of isovalent electron traps, rendering boron as the first known isovalent trap induced by cationic substitution. In the second part, thermoelectric properties of (B,Ga,In)As and (Ga,In)(N,As) are studied. It was found that although the electric-field driven electronic transport in n-type (Ga,In)(N,As) and (B,Ga,In)As differs considerably from that of n-type GaAs, the temperature-gradient driven electronic transport is very similar for the three semiconductors, despite distinct differences in the conduction band structure of (Ga,In)(N,As) and (B,Ga,In)As compared to GaAs. The third part addresses the influence of magnetic interactions on the transport properties near the metal-insulator transition (MIT). Here, two scenarios are considered: Firstly the focus is set on ZnMnSe:Cl, a representative of so called dilute magnetic semiconductors (DMS). In this material Mn(2+) ions provide a large magnetic moment due to their half filled inner 3d-shell. It is shown that magnetic interactions in conjunction with disorder effects are responsible for the unusual magnetotransport behavior found in this and other II-Mn-VI semiconductor alloys. In the second scenario, a different magnetic compound, namely InSb:Mn, is of interest. It is a representative of the III-Mn-V DMS, where the magnetic impurity Mn serves both as the source of a large localized magnetic moment and as the source of a loosely bound hole due to its acceptor character. Up to now, little is known about

  15. Electric field-induced emission enhancement and modulation in individual CdSe nanowires.

    Science.gov (United States)

    Vietmeyer, Felix; Tchelidze, Tamar; Tsou, Veronica; Janko, Boldizsar; Kuno, Masaru

    2012-10-23

    CdSe nanowires show reversible emission intensity enhancements when subjected to electric field strengths ranging from 5 to 22 MV/m. Under alternating positive and negative biases, emission intensity modulation depths of 14 ± 7% are observed. Individual wires are studied by placing them in parallel plate capacitor-like structures and monitoring their emission intensities via single nanostructure microscopy. Observed emission sensitivities are rationalized by the field-induced modulation of carrier detrapping rates from NW defect sites responsible for nonradiative relaxation processes. The exclusion of these states from subsequent photophysics leads to observed photoluminescence quantum yield enhancements. We quantitatively explain the phenomenon by developing a kinetic model to account for field-induced variations of carrier detrapping rates. The observed phenomenon allows direct visualization of trap state behavior in individual CdSe nanowires and represents a first step toward developing new optical techniques that can probe defects in low-dimensional materials.

  16. Influence of thermal agitation on the electric field induced precessional magnetization reversal with perpendicular easy axis

    Directory of Open Access Journals (Sweden)

    Hongguang Cheng

    2013-12-01

    Full Text Available We investigated the influence of thermal agitation on the electric field induced precessional magnetization switching probability with perpendicular easy axis by solving the Fokker-Planck equation numerically with finite difference method. The calculated results show that the thermal agitation during the reversal process crucially influences the switching probability. The switching probability can be achieved is only determined by the thermal stability factor Δ of the free layer, it is independent on the device dimension, which is important for the high density device application. Ultra-low error rate down to the order of 10−9 can be achieved for the device of thermal stability factor Δ of 40. Low damping factor α material should be used for the free layer for high reliability device applications. These results exhibit potential of electric field induced precessional magnetization switching with perpendicular easy axis for ultra-low power, high speed and high density magnetic random access memory (MRAM applications.

  17. Influence of thermal agitation on the electric field induced precessional magnetization reversal with perpendicular easy axis

    Energy Technology Data Exchange (ETDEWEB)

    Cheng, Hongguang, E-mail: chenghg7932@gmail.com; Deng, Ning [Institute of Microelectronics, Tsinghua University, Beijing 100084 (China)

    2013-12-15

    We investigated the influence of thermal agitation on the electric field induced precessional magnetization switching probability with perpendicular easy axis by solving the Fokker-Planck equation numerically with finite difference method. The calculated results show that the thermal agitation during the reversal process crucially influences the switching probability. The switching probability can be achieved is only determined by the thermal stability factor Δ of the free layer, it is independent on the device dimension, which is important for the high density device application. Ultra-low error rate down to the order of 10{sup −9} can be achieved for the device of thermal stability factor Δ of 40. Low damping factor α material should be used for the free layer for high reliability device applications. These results exhibit potential of electric field induced precessional magnetization switching with perpendicular easy axis for ultra-low power, high speed and high density magnetic random access memory (MRAM) applications.

  18. Transition of Magnetoresistance in Co/Alq3 Granular Film on Silicon Substrate

    Institute of Scientific and Technical Information of China (English)

    SHU Qi; ZHAO Xiao-Meng; ZHANG Yan; SHENG Peng; TANG Zhen-Yao; NI Gang

    2009-01-01

    A Co0.38 (Alq3)0.62 granular film is prepared using a co-evaporating technique on a silicon substrate with a native oxide layer. A crossover of magnetoresistance (MR) from positive to negative is observed. The positive MR ratio reaches 17.5% at room temperature (H = 50 kOe), and the negative MR ratio reaches -1.35% at 15K (H = 10 kOe). Furthermore, a metal-insulator transition is also observed. The transition of resistance and MR results from the channel switching of electron transport between the upper Co-Alq3 granular film and the inversion layer underneath. The negative MR originates from the tunneling magnetoresistance effect due to the tunneling conducting between adjacent Co granules, and the positive MR may be attributed to the transport of high mobility carriers in the SiO2/Si inversion layer.

  19. Disorder-induced structural transitions in topological insulating Ge-Sb-Te compounds

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Jeongwoo; Jhi, Seung-Hoon, E-mail: jhish@postech.ac.kr [Department of Physics, Pohang University of Science and Technology, Pohang 790-784 (Korea, Republic of)

    2015-05-21

    The mechanism for the fast switching between amorphous, metastable, and crystalline structures in chalcogenide phase-change materials has been a long-standing puzzle. Based on first-principles calculations, we study the atomic and electronic properties of metastable Ge{sub 2}Sb{sub 2}Te{sub 5} and investigate the atomic disorder to understand the transition between crystalline hexagonal and cubic structures. In addition, we study the topological insulating property embedded in these compounds and its evolution upon structural changes and atomic disorder. We also discuss the role of the surface-like states arising from the topological insulating property in the metal-insulator transition observed in the hexagonal structure.

  20. Surface Effects on the Mott-Hubbard Transition in Archetypal V{2}O{3}.

    Science.gov (United States)

    Lantz, G; Hajlaoui, M; Papalazarou, E; Jacques, V L R; Mazzotti, A; Marsi, M; Lupi, S; Amati, M; Gregoratti, L; Si, L; Zhong, Z; Held, K

    2015-12-04

    We present an experimental and theoretical study exploring surface effects on the evolution of the metal-insulator transition in the model Mott-Hubbard compound Cr-doped V{2}O{3}. We find a microscopic domain formation that is clearly affected by the surface crystallographic orientation. Using scanning photoelectron microscopy and x-ray diffraction, we find that surface defects act as nucleation centers for the formation of domains at the temperature-induced isostructural transition and favor the formation of microscopic metallic regions. A density-functional theory plus dynamical mean-field theory study of different surface terminations shows that the surface reconstruction with excess vanadyl cations leads to doped, and hence more metallic, surface states, which explains our experimental observations.

  1. Large magnetic-field-induced strains in rare earth polycrystalline Ni-Mn-Ga

    Institute of Scientific and Technical Information of China (English)

    ZHAO Zengqi; WU Shuangxia; WANG Fangshu; WANG Qiang; JIANG Liping; WANG Xinlin

    2004-01-01

    The magnetic-field-induced strains (MFIS) of polycrystalline Ni50Mn29Ga21 alloys containing Tb were studied. A large MFIS of - 1.10% was obtained under compressive prestress conditions. The addition of Tb can fine the crystal grains, enhance the bending strength obviously, and make MFIS increase further, indicating that a moderate amount of Tb does not hinder twin boundary motion and it conversely makes the material more practical.

  2. NMR studies of field induced magnetism in CeCoIn5

    Energy Technology Data Exchange (ETDEWEB)

    Graf, Matthias [Los Alamos National Laboratory; Curro, Nicholas J [UC/DAVIS; Young, Ben - Li [NATIONAL CHIAO TUNG UNIV; Urbano, Ricardo R [FLORIDA STATE UNIV

    2009-01-01

    Recent Nuclear Magnetic Resonance and elastic neutron scattering experiments have revealed conclusively the presence of static incommensurate magnetism in the field-induced B phase of CeCoIns, We analyze the NMR data assuming the hyperfine coupling to the 1n(2) nuclei is anisotropic and simulate the spectra for several different magnetic structures, The NMR data are consistent with ordered Ce moments along the [001] direction, but are relatively insensitive to the direction of the incommensurate wavevector.

  3. Ablation effects of noninvasive radiofrequency field-induced hyperthermia on liver cancer cells

    Directory of Open Access Journals (Sweden)

    Kaiyun Chen

    2016-05-01

    Full Text Available To have in-depth analysis of clinical ablation effect of noninvasive radiofrequency field-induced hyperthermia on liver cancer cells, this paper collected liver cancer patients’ treatment information from 10 hospitals during January 2010 and December 2011, from which 1050 cases of patients were randomly selected as study object of observation group who underwent noninvasive radiofrequency field-induced hyperthermia treatment; in addition, 500 cases of liver cancer patients were randomly selected as study object of control group who underwent clinical surgical treatment. After treatment was completed, three years of return visit were done, survival rates of the two groups of patients after 1 year, 2 years, and 3 years were compared, and clinical effects of radiofrequency ablation of liver cancer were evaluated. Zoom results show that the two groups are similar in terms of survival rate, and the difference is without statistical significance. 125 patients in observation group had varying degrees of adverse reactions, while 253 patients in control group had adverse reactions. There was difference between groups P < 0.05, with significant statistical significance. It can be concluded that radiofrequency ablation of liver cancer is more secure. Therefore, the results of this study fully demonstrate that liver cancer treatment with noninvasive radiofrequency field-induced hyperthermia is with safety effect and satisfactory survival rate, thus with relatively high clinical value in clinical practice.

  4. X-ray emission spectroscopy study of the Verwey transition in Fe sub 3 O sub 4

    CERN Document Server

    Moewes, A; Finkelstein, L D; Galakhov, A V; Gota, S; Gautier-Soyer, M; Rueff, J P; Hague, C F

    2003-01-01

    The temperature-dependent Verwey transition in a 500 A (111) thin film of Fe sub 3 O sub 4 (magnetite) has been studied using soft-x-ray emission spectroscopy at room temperature and below the transition temperature T sub V. The Fe L sub 2 sub , sub 3 x-ray emission spectra show an increase in the intensity of the L sub 2 emission relative to the L sub 3 emission below T sub V. This is independent of the excitation energy and is attributed to a metal-insulator transition across T sub V. Comparison of the Fe L sub 3 emission and O K alpha spectra with LDA band structure calculations supports the suggestion of charge ordering in Fe sub 3 O sub 4 at low temperature.

  5. AlGaN/GaN metal-insulator-semiconductor high-electron mobility transistors with high on/off current ratio of over 5 × 1010 achieved by ozone pretreatment and using ozone oxidant for Al2O3 gate insulator

    Science.gov (United States)

    Tokuda, Hirokuni; Asubar, Joel T.; Kuzuhara, Masaaki

    2016-12-01

    This letter describes DC characteristics of AlGaN/GaN metal-insulator-semiconductor high-electron-mobility transistors (MIS-HEMTs) with Al2O3 deposited by atomic layer deposition (ALD) as gate dielectric. Comparison was made for the samples deposited using ozone (O3) or water as oxidant. The effect of pretreatment, where O3 was solely supplied prior to depositing Al2O3, was also investigated. The MIS-HEMT with O3 pretreatment and Al2O3 gate dielectric deposited using O3 as the oxidant exhibited the most desirable characteristics with an excellent high on/off current ratio of 7.1 × 1010, and a low sub-threshold swing (SS) of 73 mV/dec.

  6. Electric field-induced optical second harmonic generation in nematic liquid crystal 5CB

    Science.gov (United States)

    Torgova, S. I.; Shigorin, V. D.; Maslyanitsyn, I. A.; Todorova, L.; Marinov, Y. G.; Hadjichristov, G. B.; Petrov, A. G.

    2014-12-01

    Electric field-induced second harmonic generation (EFISH) was studied for the liquid crystal 4-cyano-4'-pentylbiphenyl (5CB) (a nematic phase material at room temperature). The intensity of coherent SHG from 5CB cells upon DC electric field was measured for various initial orientations of the liquid crystal. The dependence of the SHG intensity on the pump beam incidence angle was obtained in transmission geometry using sample rotation method. The experimental results (the registered light intensity in the output SHG interference patterns) were theoretically modelled and analyzed.

  7. Electric Field-Induced Fluid Velocity Field Distribution in DNA Solution

    Institute of Scientific and Technical Information of China (English)

    ZHANG Ling-Yun; WANG Peng-Ye

    2008-01-01

    We present an analytical solution for fluid velocity field distribution of polyelectrolyte DNA. Both the electric field force and the viscous force in the DNA solution are considered under a suitable boundary condition. The solution of electric potential is analytically obtained by using the linearized Poisson-Boltzmann equation. The fluid velocity along the electric field is dependent on the cylindrical radius and concentration. It is shown that the electric field-induced fluid velocity will be increased with the increasing cylindrical radius, whose distribution also varies with the concentration

  8. Reversible electric field induced spectral hole filling in a doped polymer film

    Science.gov (United States)

    Gu, Wei; Hanson, David M.

    1988-09-01

    The effect of a dc electric field on persistent spectral holes in the absorption spectra of perylene doped polyvinyl butyral films has been measured. This effect is not like a typical Stark effect that is obtained with polymer films doped with polar dye molecules. Instead, a new phenomenon of reversible spectral hole filling is observed. This phenomenon is attributed to the elastic deformation of the interaction potentials of the dopant and the polymer associated with reversible field-induced tunneling in the intrinsic two-level systems. A quantitative theory of the phenomenon is proposed.

  9. THE ELASTIC FIELD INDUCED BY A HEMISPHERICAL INCLUSION IN THE HALF—SPACE

    Institute of Scientific and Technical Information of China (English)

    吴林志

    2003-01-01

    The elastic field induced by a hemispherical inclusion with uniform eigeustralns in asemi-infinite elastic medium is solved by using the Green's function method and series expansion tech-nique. The exact solutions axe presented for the displacement and stress fields which can be expressedby complete elliptic integrals of the first, second, and third kinds and hypergeometric functions. Thepresent method can be used to determine the corresponding elastic fields when the shape of the inclusionis a spherical crown or a spherical segment. Finally, numerical results axe given for the displacementand stress fields along the axis of symmetry (x3-axis).

  10. THE ELASTIC FIELD INDUCED BY A HEMISPHERICAL INCLUSION IN THE HALF-SPACE

    Institute of Scientific and Technical Information of China (English)

    吴林志

    2003-01-01

    The elastic field induced by a hemispherical inclusion with uniform eigenstrains in a semi-infinite elastic medium is solved by using the Green's function method and series expansion technique.The exact solutions are presented for the displacement and stress fields which can be expressed by complete elliptic integrals of the first,second,and third kinds and hypergeometric functions.The present method can be used to determine the corresponding elastic fields when the shape of the inclusion is a spherical crown or a spherical segment.Finally,numerical results are given for the displacement and stress fields along the axis of symmetry (x3-axis).

  11. Field-Induced Deformation as a Mechanism for Scanning Tunneling Microscopy Based Nanofabrication

    DEFF Research Database (Denmark)

    Hansen, Ole; Ravnkilde, Jan Tue; Quaade, Ulrich;

    1998-01-01

    The voltage between tip and sample in a scanning tunneling microscope (STM) results in a large electric field localized near the tip apex. The mechanical stress due to this field can cause appreciable deformation of both tip and sample on the scale of the tunnel gap. We derive an approximate...... analytical expression for this deformation and confirm the validity of the result by comparison with a finite element analysis. We derive the condition for a field-induced jump to contact of tip and sample and show that this agrees well with experimental results for material transfer between tip and sample...

  12. Analysis and design of nonlocal spin devices with electric-field-induced spin-transport acceleration

    Energy Technology Data Exchange (ETDEWEB)

    Takamura, Yota, E-mail: takamura@spin.pe.titech.ac.jp [Imaging Science and Engineering Laboratory, Tokyo Institute of Technology, Yokohama (Japan); Department of Physical Electronics, Tokyo Institute of Technology, Tokyo (Japan); Akushichi, Taiju; Shuto, Yusuke; Sugahara, Satoshi, E-mail: sugahara@isl.titech.ac.jp [Imaging Science and Engineering Laboratory, Tokyo Institute of Technology, Yokohama (Japan)

    2015-05-07

    We apply electric-field-induced acceleration for spin transport to a four-terminal nonlocal device and theoretically analyze its Hanle-effect signals. The effect of the ferromagnetic contact widths of the spin injector and detector on the signals is carefully discussed. Although Hanle-effect signals are randomized owing to the effect of the contact widths, this can be excluded by selecting an appropriate electric field for acceleration of spin transport. Spin lifetime can be correctly extracted by nonlocal devices with electric-field acceleration even using the spin injector and detector with finite contact widths.

  13. Analysis and design of nonlocal spin devices with electric-field-induced spin-transport acceleration

    Science.gov (United States)

    Takamura, Yota; Akushichi, Taiju; Shuto, Yusuke; Sugahara, Satoshi

    2015-05-01

    We apply electric-field-induced acceleration for spin transport to a four-terminal nonlocal device and theoretically analyze its Hanle-effect signals. The effect of the ferromagnetic contact widths of the spin injector and detector on the signals is carefully discussed. Although Hanle-effect signals are randomized owing to the effect of the contact widths, this can be excluded by selecting an appropriate electric field for acceleration of spin transport. Spin lifetime can be correctly extracted by nonlocal devices with electric-field acceleration even using the spin injector and detector with finite contact widths.

  14. Field induced microwave absorption in single crystal Bi (2212): Evidence for a superconductive glass state

    Energy Technology Data Exchange (ETDEWEB)

    Tyagi, S.; Gould, A.; Bhagat, S.M. (Centre for Research on Superconductivity, Dept. of Physics, Univ. of Maryland, College Park (USA)); Manheimer, M.A. (Lab. for Physical Sciences, College Park, MD (USA))

    1989-12-01

    The field induced microwave absorption P(H) at 35 GHz in Bi 2212 micaceous single crystals exhibits remarkable variations as temperature is increased from 1.3 K to Tc. For T< or approx.16 K, the hysteresis loops are highly reminiscent of those observed in spin glasses. At 30< or approx.T< or approx.50 K, they resemble those of a Type II superconductor. As suggested by the magnetization data, the micaceous nature causes a large enhancement in P(H) for 50

  15. A procedure to estimate the electric field induced in human body exposed to unknown magnetic sources.

    Science.gov (United States)

    Wang, Wencui; Bottauscio, Oriano; Chiampi, Mario; Giordano, Domenico; Zilberti, Luca

    2013-04-01

    The paper proposes and discusses a boundary element procedure able to predict the distribution of the electric field induced in a human body exposed to a low-frequency magnetic field produced by unknown sources. As a first step, the magnetic field on the body surface is reconstructed starting from the magnetic field values detected on a closed surface enclosing the sources. Then, the solution of a boundary value problem provides the electric field distribution inside the human model. The procedure is tested and validated by considering different non-uniform magnetic field distributions generated by a Helmholtz coil system as well as different locations of the human model.

  16. A field induced guide-antiguide modulator of GaAs-AlGaAs

    Science.gov (United States)

    Huang, T. C.; Chung, Y.; Young, D. B.; Dagli, N.; Coldren, L. A.

    1991-01-01

    A guide-antiguide modulator of GaAs-AlGaAs using the electric-field-induced waveguide concept was demonstrated. The device was formed with a central waveguide electrode sandwiched between two antiguide electrodes on the surface of a p-i-n multiple quantum well (MQW). Switching between lateral guiding and antiguiding was accomplished by reverse biasing either the central electrode or the adjacent electrodes to increase the index beneath these respective regions. The on-off ratio was measured to be 20:1 with a propagation loss of the on-state of about 5 dB/mm.

  17. Tuning the field-induced magnetic transition in a layered cobalt phosphonate by reversible dehydration-hydration process.

    Science.gov (United States)

    Yang, Ting-Hai; Liao, Yi; Zheng, Li-Min; Dinnebier, Robert E; Su, Yan-Hui; Ma, Jing

    2009-06-07

    A layered cobalt phosphonate, Co(2-pmp)(H(2)O)(2) (1) (2-pmpH(2) = 2-pyridylmethylphosphonic acid) is reported, which provides the first example of metamagnetic cobalt system that shows reversible changes in both structures and magnetic behaviors upon dehydration-hydration process.

  18. 3D-xy critical properties of YBa{sub 2}Cu{sub 4}O{sub 8} and magnetic-field-induced 3D to 1D crossover

    Energy Technology Data Exchange (ETDEWEB)

    Weyeneth, S; Schneider, T; Keller, H [Physik-Institut der Universitaet Zuerich, Winterthurerstrasse 190, CH-8057 Zuerich (Switzerland); Bukowski, Z; Karpinski, J [Laboratory for Solid State Physics, ETH Zuerich, CH-8093 Zuerich (Switzerland)], E-mail: wstephen@physik.uzh.ch

    2008-08-27

    We present reversible magnetization data of a YBa{sub 2}Cu{sub 4}O{sub 8} single crystal and analyze the evidence for 3D-xy critical behavior and a magnetic-field-induced 3D to 1D crossover. Remarkable consistency with these phenomena is observed in agreement with a magnetic-field-induced finite size effect, whereupon the correlation length transverse to the applied magnetic field cannot grow beyond the limiting magnetic length scale L{sub H} ({phi}{sub 0}/(aH)){sup 1/2}. By applying the appropriate scaling form we obtain the zero-field critical temperature, the 3D to 1D crossover, the vortex melting line and the universal ratios of the related scaling variables. Accordingly there is no continuous phase transition in the (H,T) plane along the H{sub c2} lines as predicted by the mean-field treatment.

  19. Anomalous vortex dynamics in κ-[bis(ethylenedithio)tetrathiafulvalene]2Cu[N(CN)2]Br: Evidence for field-induced magnetic order and unconventional superconductivity

    Science.gov (United States)

    Lahaise, U. G.; Chen, Qun; de Long, L. E.; Brock, C. P.; Wang, H. H.; Carlson, K. D.; Schlueter, J. A.; Williams, J. M.

    1995-02-01

    Anisotropic superconducting flux-line behavior of single-crystal κ-[bis(ethylenedithio)tetrathiaful- valene]2Cu[N(CN)2]Br has been studied with dc magnetization and vibrating-reed (VR) techniques. A peak at T*(H) in the temperature dependence of the VR inverse quality factor 1/Q exhibits a shoulder for magnetic fields 0<μ0H<=0.5 T parallel to the conducting ac plane. The shoulder becomes unresolved near a kink in T*(H) at μ0H~=0.7 T. Discontinuities in 1/Q and the VR frequency shift occur for 0.1<=μ0H<=1.3 T applied perpendicular to the ac plane and temperatures T<=20 K, well into the normal state. These anomalies are preliminary evidence for a field-induced magnetic phase transition and unconventional superconductivity.

  20. Field-induced alignment of a smectic-A phase: a time-resolved x-ray diffraction investigation.

    Science.gov (United States)

    Bras, W; Emsley, J W; Levine, Y K; Luckhurst, G R; Seddon, J M; Timimi, B A

    2004-09-01

    The field-induced alignment of a smectic-A phase is, in principle, a complicated process involving the director rotation via the interaction with the field and the layer rotation via the molecular interactions. Time-resolved nuclear magnetic resonance spectroscopy has revealed this complexity in the case of the director alignment, but provides no direct information on the motion of the layers. Here we describe a time-resolved x-ray diffraction experiment using synchrotron radiation to solve the challenging problem of capturing the diffraction pattern on a time scale which is fast in comparison with that for the alignment of the smectic layers. We have investigated the alignment of the smectic-A phase of 4-octyl-4(')-cyanobiphenyl by a magnetic field. The experiment consists of creating a monodomain sample of the smectic-A phase by slow cooling from the nematic phase in a magnetic field with a flux density of 7 T. The sample is then turned quickly through an angle phi(0) about an axis parallel to the x-ray beam direction but orthogonal to the field. A sequence of two-dimensional small angle x-ray diffraction patterns are then collected at short time intervals. Experiments were carried out for different values of phi(0), and at different temperatures. The results show that the alignment behavior changes fundamentally when phi(0) exceeds 45 degrees, and that there is a sharp change in the alignment process when the temperature is less than 3 degrees C below the smectic-A-nematic transition. The results of the x-ray experiments are in broad agreement with the NMR results, but reveal major phenomena concerning the maintenance of the integrity of the smectic-A layer structure during the alignment process. (c) 2004 American Institute of Physics