HKU Scholars Hubhttp://hub.hku.hkThe DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material.Tue, 18 Jan 2022 02:41:17 GMT2022-01-18T02:41:17Z502051- Conductance modulations in spin field-effect transistors under finite bias voltageshttp://hdl.handle.net/10722/43421Title: Conductance modulations in spin field-effect transistors under finite bias voltages
Authors: Hu, L; Gao, J; Shen, SQ
Abstract: The conductance modulations in spin field-effect transistors under finite bias voltages were studied. It was shown that when a finite bias voltage is applied between two terminals of a spin field-effect transistor, the spin precession states of injected spin-polarized electrons in the semiconductor channel of the device will depend not only on the gate-voltage controlled Rashba spin-orbit coupling but also on the bias voltage and, hence, the conductance modulation in the device due to Rashba spin-orbit coupling may also depend sensitively on the bias voltage.
Thu, 01 Jan 2004 00:00:00 GMThttp://hdl.handle.net/10722/434212004-01-01T00:00:00Z
- Quadratic magnetic field dependence of magnetoelectric photocurrenthttp://hdl.handle.net/10722/134446Title: Quadratic magnetic field dependence of magnetoelectric photocurrent
Authors: Dai, J; Lu, HZ; Shen, SQ; Zhang, FC; Cui, X
Abstract: We experimentally study the spin and electric photocurrents excited by a linearly polarized light via direct interband transitions in an InGaAs/InAlAs quantum well. In the absence of a magnetic field, the linearly polarized light induces a pure spin current due to the spin-orbit coupling, which may be transformed into a measurable electric current by applying an in-plane magnetic field. The induced electric photocurrent is linear with the in-plane magnetic field. Here, we report a quadratic magnetic field dependence of the photocurrent in the presence of an additional perpendicular component of the magnetic field. We attribute the observation to the Hall effect of magnetoelectric photocurrent. © 2011 American Physical Society.
Sat, 01 Jan 2011 00:00:00 GMThttp://hdl.handle.net/10722/1344462011-01-01T00:00:00Z
- Extrinsic anomalous Hall conductivity of a topologically nontrivial conduction bandhttp://hdl.handle.net/10722/189337Title: Extrinsic anomalous Hall conductivity of a topologically nontrivial conduction band
Authors: Lu, HZ; Shen, SQ
Tue, 01 Jan 2013 00:00:00 GMThttp://hdl.handle.net/10722/1893372013-01-01T00:00:00Z
- Surface edge state and half-quantized Hall conductance in topological insulatorshttp://hdl.handle.net/10722/175193Title: Surface edge state and half-quantized Hall conductance in topological insulators
Authors: Chu, RL; Shi, J; Shen, SQ
Abstract: We study the surface local density of states and the transport properties of a three-dimensional (3D) topological insulator (TI) in the presence of a uniform spin-splitting Zeeman field. We find chiral edge states exist on the gapped surfaces of the 3D TI, which can be considered as interface states between domains of massive and massless Dirac fermions. Effectively these states are the result of splitting of a perfect interface conducting channel. This picture is confirmed by the Landauer-Büttiker calculations in four-terminal Hall bars made of 3D TIs. It is demonstrated that the difference between the clockwise and counterclockwise transmission coefficients of the two neighboring terminals is approximately one-half, which suggests that the half-quantized Hall conductance can be manifested in an appropriate experimental setup. We also predict that the quantized anomalous Hall effect exists in thin films of TIs where such effective Zeeman felds are present. © 2011 American Physical Society.
Sat, 01 Jan 2011 00:00:00 GMThttp://hdl.handle.net/10722/1751932011-01-01T00:00:00Z
- Theoretical evidence of the Berry-phase mechanism in anomalous Hall transport: First-principles studies of Cu Cr2 Se4-x Brxhttp://hdl.handle.net/10722/175049Title: Theoretical evidence of the Berry-phase mechanism in anomalous Hall transport: First-principles studies of Cu Cr2 Se4-x Brx
Authors: Yao, Y; Liang, Y; Xiao, D; Niu, Q; Shen, SQ; Dai, X; Fang, Z
Abstract: To justify the origin of the anomalous Hall effect (AHE), it is highly desirable to have the system parameters tuned continuously. By quantitative calculations, we show that the doping-dependent sign reversal in Cu Cr2 Se4-x Brx, observed but not understood, is nothing but direct evidence for the Berry-phase mechanism of the AHE. Systematic calculations explain well the experiment data for the whole doping range where the impurity scattering rate is changed by several orders with Br substitution. Further sign change is also predicted, which may be tested by future experiments. © 2007 The American Physical Society.
Mon, 01 Jan 2007 00:00:00 GMThttp://hdl.handle.net/10722/1750492007-01-01T00:00:00Z
- Current noise cross correlation mediated by Majorana bound stateshttp://hdl.handle.net/10722/207286Title: Current noise cross correlation mediated by Majorana bound states
Authors: Lu, H; Lu, H; Shen, S
Wed, 01 Jan 2014 00:00:00 GMThttp://hdl.handle.net/10722/2072862014-01-01T00:00:00Z
- Spin transverse force on spin current in an electric fieldhttp://hdl.handle.net/10722/146197Title: Spin transverse force on spin current in an electric field
Authors: Shen, SQ
Abstract: As a relativistic quantum mechanical effect, it is shown that the electron field exerts a transverse force on an electron spin 1/2 only if the electron is moving. The spin force, analogue to the Lorentz for an electron charge in a magnetic field, is perpendicular to the electric field and the spin current whose spin polarization is projected along the electric field. This spin-dependent force can be used to understand the Zitterbewegung of the electron wave packet with spin-orbit coupling and is relevant to the generation of the charge Hall effect driven by the spin current in semiconductors. © 2005 The American Physical Society.
Sat, 01 Jan 2005 00:00:00 GMThttp://hdl.handle.net/10722/1461972005-01-01T00:00:00Z
- Finite-Temperature Conductivity and Magnetoconductivity of Topological Insulatorshttp://hdl.handle.net/10722/197847Title: Finite-Temperature Conductivity and Magnetoconductivity of Topological Insulators
Authors: Lu, H; Shen, S
Wed, 01 Jan 2014 00:00:00 GMThttp://hdl.handle.net/10722/1978472014-01-01T00:00:00Z
- Edge States and Integer Quantum Hall Effect in Topological Insulator Thin Filmshttp://hdl.handle.net/10722/218814Title: Edge States and Integer Quantum Hall Effect in Topological Insulator Thin Films
Authors: ZHANG, S; Lu, H; Shen, S
Thu, 01 Jan 2015 00:00:00 GMThttp://hdl.handle.net/10722/2188142015-01-01T00:00:00Z
- Propagation of sound and supersonic bright solitons in superfluid fermi gases in BCS-BEC crossoverhttp://hdl.handle.net/10722/125265Title: Propagation of sound and supersonic bright solitons in superfluid fermi gases in BCS-BEC crossover
Authors: Wen, W; Shen, SQ; Huang, G
Abstract: We investigate the linear and nonlinear sound propagations in a cigar-shaped superfluid Fermi gas with a large particle number. We first solve analytically the eigenvalue problem of linear collective excitations and provide explicit expressions of all eigenvalues and eigenfunctions, which are valid for all superfluid regimes in the Bardeen-Cooper-Schrieffer-Bose-Einstein condensation (BCS-BEC) crossover. The linear sound speed obtained agrees well with that of a recent experimental measurement. We then consider a weak nonlinear excitation and show that the time evolution of the excitation obeys a Korteweg de Vries equation. Different from the result obtained in quasi-one-dimensional case studied previously, where subsonic dark solitons are obtained via the balance between quantum pressure and nonlinear effect, we demonstrate that bright solitons with supersonic propagating velocity can be generated in the present three-dimensional system through the balance between a waveguidelike dispersion and the interparticle interaction. The supersonic bright solitons obtained display different physical properties in different superfluid regimes and hence can be used to characterize superfluid features of the BCS-BEC crossover. © 2010 The American Physical Society.
Fri, 01 Jan 2010 00:00:00 GMThttp://hdl.handle.net/10722/1252652010-01-01T00:00:00Z
- Topological crystalline antiferromagnetic state in tetragonal FeShttp://hdl.handle.net/10722/249676Title: Topological crystalline antiferromagnetic state in tetragonal FeS
Authors: Hao, NN; Zheng, FW; Zhang, P; Shen, S
Sun, 01 Jan 2017 00:00:00 GMThttp://hdl.handle.net/10722/2496762017-01-01T00:00:00Z
- Hidden edge Dirac point and robust quantum edge transport in InAs/GaSb quantum wellshttp://hdl.handle.net/10722/251564Title: Hidden edge Dirac point and robust quantum edge transport in InAs/GaSb quantum wells
Authors: LI, C; Zhang, SB; Shen, S
Mon, 01 Jan 2018 00:00:00 GMThttp://hdl.handle.net/10722/2515642018-01-01T00:00:00Z
- Generalized valence bond state and solvable models for spin-1/2 systems with orbital degeneracyhttp://hdl.handle.net/10722/43334Title: Generalized valence bond state and solvable models for spin-1/2 systems with orbital degeneracy
Authors: Shen, SQ
Abstract: A spin-1/2 system with double orbital degeneracy may possess SU(4) symmetry. According to the group theory a global SU(4) singlet state can be expressed as a linear combination of all possible configurations consisting of four-site SU(4) singlets. Following Andersion's idea for spin-1/2 system, we propose that the ground state for the antiferromagnetic SU(4) model is an SU(4)-resonating valence-bond (RVB) state. A short-range SU(4)-RVB state is a spin and orbital liquid, and its elementary excitations has an energy gap. We construct a series of solvable models that ground states are short-range SU(4)-RVB states. The results are generalized to the antiferromagnetic SU(N) models.
Mon, 01 Jan 2001 00:00:00 GMThttp://hdl.handle.net/10722/433342001-01-01T00:00:00Z
- Observation of electric current induced by optically injected spin currenthttp://hdl.handle.net/10722/80580Title: Observation of electric current induced by optically injected spin current
Authors: Cui, XD; Shen, SQ; Li, J; Ji, Y; Ge, W; Zhang, FC
Abstract: Linearly polarized light at normal incidence injects a spin current into a strip of two-dimensional electron gas with Rashba spin-orbit coupling. The authors report observation of an electric current when such light is shed on the vincinity of the junction in a crossbar-shaped InGaAsInAlAs quantum well Rashba system. The polarization dependence of this electric current was experimentally observed to be the same as that of the spin current. The authors attribute the observed electric current to the scattering of the optically injected spin current at the crossing. © 2007 American Institute of Physics.
Mon, 01 Jan 2007 00:00:00 GMThttp://hdl.handle.net/10722/805802007-01-01T00:00:00Z
- Formation of energy gap in high-dimensional spin-orbital liquidshttp://hdl.handle.net/10722/42464Title: Formation of energy gap in high-dimensional spin-orbital liquids
Authors: Shen, SQ; Zhang, GM
Abstract: A Schwinger boson mean-field theory is developed for spin liquids in a symmetric spin-orbital model in higher dimensions. Spin, orbital and coupled spin-orbital operators are treated equally. We evaluate the dynamic correlation functions and collective excitations spectra. As the collective excitations have a finite energy gap, we conclude that the ground state is a spin-orbital liquid with a two-fold degeneracy, which breaks the discrete spin-orbital symmetry. Based on this conclusion, we propose that broken symmetry or symmetric frustration instead of geometric quantum frustration provides a new route to explore the spin liquid states. Possible relevence of this spin liquid state to several realistic systems, such as CaV 4O 9 and Na 2Sb 2Ti 2O, are discussed.
Tue, 01 Jan 2002 00:00:00 GMThttp://hdl.handle.net/10722/424642002-01-01T00:00:00Z
- Vacancy-induced bound states in topological insulatorshttp://hdl.handle.net/10722/139648Title: Vacancy-induced bound states in topological insulators
Authors: Shan, WY; Lu, J; Lu, HZ; Shen, SQ
Abstract: We present an exact solution of a modified Dirac equation for topological insulator in the presence of a hole or vacancy to demonstrate that vacancies can induce bound states in the band gap of topological insulators. They arise due to the Z 2 classification of time-reversal invariant insulators. Coexistence of the in-gap bound states and the edge or surface states in topological insulators suggests that imperfections may affect transport properties of topological insulators via additional bound states near the system boundary. © 2011 American Physical Society.
Sat, 01 Jan 2011 00:00:00 GMThttp://hdl.handle.net/10722/1396482011-01-01T00:00:00Z
- Crossover from Majorana edge- to end-states in quasi-one-dimensional p-wave superconductorshttp://hdl.handle.net/10722/139658Title: Crossover from Majorana edge- to end-states in quasi-one-dimensional p-wave superconductors
Authors: Zhou, B; Shen, SQ
Abstract: In a recent work, it was demonstrated by means of numerical diagonalization that the Majorana end states can be localized at opposite ends of a sample of an ideal spinless p-wave superconductor with the strip geometry beyond the strict one-dimensional limit. Here, we reexamine this issue and study the topological quantum phase transition in the same system. We give the phase diagrams of the presence of Majorana end modes by using of Z 2 topological index. It is found that the topological property of a strip geometry will change in an oscillatory way with respect of the sample width. © 2011 American Physical Society.
Sat, 01 Jan 2011 00:00:00 GMThttp://hdl.handle.net/10722/1396582011-01-01T00:00:00Z
- Signatures of the Adler–Bell–Jackiw chiral anomaly in a Weyl fermion semimetalhttp://hdl.handle.net/10722/223884Title: Signatures of the Adler–Bell–Jackiw chiral anomaly in a Weyl fermion semimetal
Authors: Zhang, CL; Xu, SY; Belopolski, I; Yuan, Z; Lin, Z; Tong, B; Bian, G; Alidoust, N; Lee, CC; Huang, SM; Chang, TR; Chang, G; Hsu, CH; Jeng, HT; Neupane, M; Sanchez, DS; Zheng, H; Wang, J; Lin, H; Zhang, C; Lu, HZ; Shen, S; Neupert, T; Zahid Hasan, M; Jia, S
Fri, 01 Jan 2016 00:00:00 GMThttp://hdl.handle.net/10722/2238842016-01-01T00:00:00Z
- Effects of spin imbalance on the electric-field-driven quantum dissipationless spin current in p-doped semiconductorshttp://hdl.handle.net/10722/43454Title: Effects of spin imbalance on the electric-field-driven quantum dissipationless spin current in p-doped semiconductors
Authors: Hu, L; Gao, J; Shen, SQ
Abstract: It was proposed recently by Murakami et al. [Science 301, 1348 (2003)] that in a large class of p-doped semiconductors, an applied electric field can drive a quantum dissipationless spin current in the direction perpendicular to the electric field. In this paper we investigate the effects of spin imbalance on this intrinsic spin Hall effect. We show that in a real sample with boundaries, due to the presence of spin imbalance near the edges of the sample, the spin Hall conductivity is not a constant but a sensitively position-dependent quantity, and due to this fact, in order to take the effects of spin imbalance properly into account, a microscopic calculation of both the quantum dissipationless spin Hall current and the spin accumulation on an equal footing is thus required. Based on such a microscopic calculation, a detailed discussion of the effects of spin imbalance on the intrinsic spin Hall effect in thin slabs of p-doped semiconductors are presented.
Thu, 01 Jan 2004 00:00:00 GMThttp://hdl.handle.net/10722/434542004-01-01T00:00:00Z
- High-field Magnetoconductivity of Topological Semimetals with Short-range Potentialhttp://hdl.handle.net/10722/214487Title: High-field Magnetoconductivity of Topological Semimetals with Short-range Potential
Authors: Lu, H; ZHANG, S; Shen, S
Thu, 01 Jan 2015 00:00:00 GMThttp://hdl.handle.net/10722/2144872015-01-01T00:00:00Z
- Weak Antilocalization and Localization in Disordered and Interacting Weyl Semimetalshttp://hdl.handle.net/10722/214478Title: Weak Antilocalization and Localization in Disordered and Interacting Weyl Semimetals
Authors: Lu, H; Shen, S
Thu, 01 Jan 2015 00:00:00 GMThttp://hdl.handle.net/10722/2144782015-01-01T00:00:00Z
- Comment on 'Lagrange-multiplier method in correlated-electron systems: Exact diagonalization study'http://hdl.handle.net/10722/43263Title: Comment on 'Lagrange-multiplier method in correlated-electron systems: Exact diagonalization study'
Authors: Shen, SQ
Abstract: We discuss the Lagrange-multiplier method in a many-body system, and how to apply the Lagrange multiplier correctly to realize quantum constraint in a Hamiltonian for a quantum system. It is pointed out that the discussion in Yanagisawa’s paper [Phys. Rev. B 57, 6208 (1998)] lacks a basic knowledge of mathematics, and that his conclusion is generally wrong.
Fri, 01 Jan 1999 00:00:00 GMThttp://hdl.handle.net/10722/432631999-01-01T00:00:00Z
- Double quantum dot as detector of spin biashttp://hdl.handle.net/10722/80808Title: Double quantum dot as detector of spin bias
Authors: Sun, QF; Xing, Y; Shen, SQ
Abstract: It was proposed that a double quantum dot can be used as a detector of the spin bias. Electron transport through a double quantum dot is theoretically investigated when a pure spin bias is applied on two conducting leads in contact with the quantum dot. It is found that the spin polarization in the left and right dots may be spontaneously induced, while the intradot levels are located within the spin bias window and breaks the left-right symmetry of the two quantum dots. As a result, a large current emerges. For an open external circuit, a charge bias instead of a charge current will be induced at equilibrium, which is believed to be measurable according to the current nanotechnology. This method may provide a practical and whole electrical approach to detect the spin bias (or the spin current) by measuring the charge bias or current in a double quantum dot. © 2008 The American Physical Society.
Tue, 01 Jan 2008 00:00:00 GMThttp://hdl.handle.net/10722/808082008-01-01T00:00:00Z
- Spin-bias driven magnetization reversal and nondestructive detection in a single molecular magnethttp://hdl.handle.net/10722/59664Title: Spin-bias driven magnetization reversal and nondestructive detection in a single molecular magnet
Authors: Lu, HZ; Zhou, B; Shen, SQ
Abstract: The magnetization reversal in a single molecular magnet (SMM) weakly coupled to an electrode with spin-dependent splitting of chemical potentials (spin bias) is theoretically investigated by means of the rate equation. A microscopic mechanism for the reversal is demonstrated by the avalanche dynamics at the reversal point. The magnetization as a function of the spin bias shows hysteresis loops tunable by the gate voltage and varying with temperature. The nondestructive measurement to the orientation of giant spin in SMM is presented by measuring the fully polarized electric current in the response to a small spin bias. For Mn12 ac molecule, its small transverse anisotropy only slightly violates the results above. The situation when there is an angle between the easy axis of the SMM and the spin-quantization direction of the electrode is also studied. © 2009 The American Physical Society.
Thu, 01 Jan 2009 00:00:00 GMThttp://hdl.handle.net/10722/596642009-01-01T00:00:00Z
- Charge ordering and phase separation in the infinite dimensional extended Hubbard modelhttp://hdl.handle.net/10722/43460Title: Charge ordering and phase separation in the infinite dimensional extended Hubbard model
Authors: Tong, NH; Shen, SQ; Bulla, R
Abstract: We study the extended Hubbard model with both on-site (U) and nearest neighbor (V) Coulomb repulsion using the exact diagonalization method within the dynamical mean field theory. For a fixed U (U=2.0), the T-n phase diagrams are obtained for V=1.4 and V=1.2, at which the ground state of n=1/2 system is charge-ordered and charge-disordered, respectively. In both cases, robust charge order is found at finite temperature and in an extended filling regime around n=1/2. The order parameter changes nonmonotonously with temperature. For V=1.4, phase separation between charge-ordered and charge-disordered phases is observed in the low temperature and n<0.5 regime. It is described by an "S"-shaped structure of the n-μ curve. For V =1.2, the ground state is charge-disordered, and a reentrant charge-ordering transition is observed for 0.42<n<0.68. The relevance of our results to experiments for doped manganites is discussed.
Thu, 01 Jan 2004 00:00:00 GMThttp://hdl.handle.net/10722/434602004-01-01T00:00:00Z
- Ordered valence-bond states in symmetric two-dimensional spin-orbital systemshttp://hdl.handle.net/10722/42461Title: Ordered valence-bond states in symmetric two-dimensional spin-orbital systems
Authors: Zhang, GM; Shen, SQ
Abstract: A reduced effective spin-orbital Hamiltonian in a symmetric spin-orbital system was derived by introducing the SU(4) Schwinger boson representation. After introducing a symmetric pairing VB order parameter, a mean field theory was developed, leading to a quantum disordered liquid state with a finite gap in the collective excitations in 1D and, on a 2D square lattice.
Mon, 01 Jan 2001 00:00:00 GMThttp://hdl.handle.net/10722/424612001-01-01T00:00:00Z
- Nonlocal noise cross correlation mediated by entangled Majorana fermionshttp://hdl.handle.net/10722/175216Title: Nonlocal noise cross correlation mediated by entangled Majorana fermions
Authors: Lü, HF; Lu, HZ; Shen, SQ
Abstract: Due to their nonlocality, qubits nested in Majorana bound states may be the key to realize decoherence-free quantum computation. Majorana bound states could be achieved at the ends of a one-dimensional topological superconductor. However, when the bound states couple directly to electron reservoirs their nonlocal correlation is quenched by local Andreev reflections. Here we propose a scheme to generate nonlocal noise cross correlation between two well-separated quantum dots, mediated by a pair of Majorana bound states. Both positive and negative cross correlations can be obtained by tuning the gate voltages applied to the dots. Within a limited range of finite temperatures, the cross correlation is not suppressed by thermal fluctuations. Furthermore, we show how the local Andreev reflections suppress the noise cross correlation when multiple dot energy levels are coupled to the Majorana bound states. The measurable cross correlation is expected to serve as a sensitive indicator for the generation of Majorana fermions. © 2012 American Physical Society.
Sun, 01 Jan 2012 00:00:00 GMThttp://hdl.handle.net/10722/1752162012-01-01T00:00:00Z
- Spin-orbit scattering in quantum diffusion of massive Dirac fermionshttp://hdl.handle.net/10722/175220Title: Spin-orbit scattering in quantum diffusion of massive Dirac fermions
Authors: Shan, WY; Lu, HZ; Shen, SQ
Abstract: We theoretically study the effects of spin-orbit scattering on weak (anti)localization in two-dimensional massive Dirac systems. We clarify that weak antilocalization and localization of a single massive Dirac cone come from the diffusion of a singlet Cooperon in the massless limit and one of triplet Cooperons in the large-mass limit, respectively. Spin-orbit scattering behaves like random magnetic scattering to the triplet Cooperon, and suppresses the weak localization in the large-mass regime, different from in conventional systems where spin-orbit scattering leads to a crossover from weak localization to antilocalization. This behavior suggests an experiment to detect the weak localization of bulk subbands in topological insulator thin films, in which an enhancement of "weak antilocalization" is expected after doping heavy-element impurities. Finally, we compare the conventional electron and Dirac fermion systems in the quantum diffusion transport under ordinary, spin-orbit, and magnetic scattering. © 2012 American Physical Society.
Sun, 01 Jan 2012 00:00:00 GMThttp://hdl.handle.net/10722/1752202012-01-01T00:00:00Z
- Spintronic Faraday rotation spectroscopy and geometrical modulation of spin current in an Aharonov-Casher ringhttp://hdl.handle.net/10722/43458Title: Spintronic Faraday rotation spectroscopy and geometrical modulation of spin current in an Aharonov-Casher ring
Authors: Ma, Z; Li, P; Shen, SQ
Abstract: We study the ballistic spin transmission through an AC ring between two ferromagnetic filter-electrodes in the presence of spin-orbit interaction, theoretically. It is shown that the spin precession of polarized electrons can be controlled via a cylindrically symmetric electric field, and the sequence of the polarized conductance depends on the relative orientation of magnetization between the left and right filters. The injected spin-polarized electrons can be blocked completely for the special values of electric field and angle of texture, which makes the magnetoresistance to be drastically enhanced. We also propose an interference scheme to detect the geometric phase.
Thu, 01 Jan 2004 00:00:00 GMThttp://hdl.handle.net/10722/434582004-01-01T00:00:00Z
- Surface and edge states in topological semimetalshttp://hdl.handle.net/10722/136766Title: Surface and edge states in topological semimetals
Authors: Chu, RL; Shan, WY; Lu, J; Shen, SQ
Abstract: We study the topologically nontrivial semimetals by means of the six-band Kane model. Existence of surface states is explicitly demonstrated by calculating the local density of states (LDOS) on the material surface. In the strain-free condition, surface states are divided into two parts in the energy spectrum, one part is in the direct gap, the other part including the crossing point of surface state Dirac cone is submerged in the valence band. We also show how uniaxial strain induces an insulating band gap and raises the crossing point from the valence band into the band gap, making the system a true topological insulator. We predict the existence of helical edge states and spin Hall effect in the thin-film topological semimetals, which could be tested by future experiments. Disorder is found to significantly enhance the spin-Hall effect in the valence band of the thin films. © 2011 American Physical Society.
Sat, 01 Jan 2011 00:00:00 GMThttp://hdl.handle.net/10722/1367662011-01-01T00:00:00Z
- Orbital ordering and two ferromagnetic phases in low-doped La 1-xSr xMnO 3http://hdl.handle.net/10722/43298Title: Orbital ordering and two ferromagnetic phases in low-doped La 1-xSr xMnO 3
Authors: Shen, SQ; Gu, RY; Wang, QH; Wang, ZD; Xie, XC
Abstract: We present a theory for the transition between two ferromagnetic phases observed experimentally in lightly doped La 1-xSr xMnO 3. Starting from an electronic model, the instabilities to various types of orbital orderings are studied within the random-phase approximation. In most cases, the instabilities occur in the region of strong correlations. A phase diagram is calculated in the case of strong correlation by means of the projected perturbation technique and the Schwinger boson technique. A phase transition between two types of orbital ordering occurs at a low doping, which may be closely relevant to recent experimental observations.
Sat, 01 Jan 2000 00:00:00 GMThttp://hdl.handle.net/10722/432982000-01-01T00:00:00Z
- Contractor renormalization group theory of SU(N) chains and laddershttp://hdl.handle.net/10722/43474Title: Contractor renormalization group theory of SU(N) chains and ladders
Authors: Li, P; Shen, SQ
Abstract: The contractor renormalization group (CORE) method is applied to the SU(N) chain and ladders in this paper. In our designed schemes, we show that these two classes of systems can return to their original form of Hamiltonian after CORE transformation. Successive iteration of the transformation leads to a fixed point so that the ground state energy and the energy gap to the ground state can be deduced. The result of SU(N) chain is compared with the one by Bethe ansatz method. The transformation on spin-1 2 ladders gives a finite gap in the excited energy spectra to the ground state in an intuitive way. The application to SU(3) ladders is also discussed. © 2005 The American Physical Society.
Sat, 01 Jan 2005 00:00:00 GMThttp://hdl.handle.net/10722/434742005-01-01T00:00:00Z
- Influence of spin transfer and contact resistance on measurement of the spin Hall effecthttp://hdl.handle.net/10722/43401Title: Influence of spin transfer and contact resistance on measurement of the spin Hall effect
Authors: Hu, L; Gao, J; Shen, SQ
Abstract: When a longitudinal spin-unpolarized charge current flows in a thin slab of nonmagnetic metal with strong spin-orbit coupling of conduction electrons, a transverse spin Hall voltage can be generated between both edges of the sample, and the spin Hall voltage can be detected by the measurement of an ordinary Hall voltage produced in a transverse metal strip which connects both edges of the sample. In this paper, we discuss the influences of spin transfer and contact resistances between the longitudinal sample and the transverse metal strip on the measurement of the spin Hall voltage. We show that, due to the spin transfer between the longitudinal sample and the transverse metal strip, the magnitude of the spin Hall voltage produced in the longitudinal sample and the magnitude of the ordinary Hall voltage produced in the transverse metal strip and the relation between them will all strongly depend on the contact resistances, thus in order to detect the spin Hall voltage correctly through the measurement of the ordinary Hall voltage, the influences of spin transfer and contact resistance need to be taken into account.
Wed, 01 Jan 2003 00:00:00 GMThttp://hdl.handle.net/10722/434012003-01-01T00:00:00Z
- Weak localization of bulk channels in topological insulator thin filmshttp://hdl.handle.net/10722/147670Title: Weak localization of bulk channels in topological insulator thin films
Authors: Lu, HZ; Shen, SQ
Abstract: Weak antilocalization (WAL) is expected whenever strong spin-orbit coupling or scattering comes into play. Spin-orbit coupling in the bulk states of a topological insulator is very strong, enough to result in the topological phase transition. However, the recently observed WAL in topological insulators seems to have an ambiguous origin from the bulk states. Starting from the effective model for three-dimensional topological insulators, we find that the lowest two-dimensional (2D) bulk subbands of a topological insulator thin film can be described by the modified massive Dirac model. We derive the magnetoconductivity formula for both the 2D bulk subbands and surface bands. Because with relatively large gap, the 2D bulk subbands may lie in the regimes where the unitary behavior or even weak localization (WL) is also expected, instead of always WAL. As a result, the bulk states may contribute small magnetoconductivity or even compensate the WAL from the surface states. Inflection in magnetoconductivity curves may appear when the bulk WL channels outnumber the surface WAL channels, providing a signature of the weak localization from the bulk states. © 2011 American Physical Society.
Sat, 01 Jan 2011 00:00:00 GMThttp://hdl.handle.net/10722/1476702011-01-01T00:00:00Z
- Disorder-induced topological phase transitions in two-dimensional spin-orbit coupled superconductorshttp://hdl.handle.net/10722/238703Title: Disorder-induced topological phase transitions in two-dimensional spin-orbit coupled superconductors
Authors: Qin, W; Xiao, D; Chang, K; Shen, S; Zhang, ZY
Fri, 01 Jan 2016 00:00:00 GMThttp://hdl.handle.net/10722/2387032016-01-01T00:00:00Z
- Transverse electric current induced by optically injected spin current in a cross-shaped InGaAsInAlAs systemhttp://hdl.handle.net/10722/45263Title: Transverse electric current induced by optically injected spin current in a cross-shaped InGaAsInAlAs system
Authors: Li, J; Dai, X; Shen, SQ; Zhang, FC
Abstract: We examine the electric response of a linearly polarized light normally shed on a cross-shaped quasi-two-dimensional InGaAsInAlAs system with structure inversion asymmetry. The photoexcited conduction electrons carry a pure spin current with in-plane spin polarization due to the Rashba spin-orbit interaction. We use the Landauer-Büttiker formalism to show that this spin current induces two inward or outward transverse charge currents, which are observable in experiments. This effect may serve as an experimental probe of certain types of spin current. © 2006 American Institute of Physics.
Sun, 01 Jan 2006 00:00:00 GMThttp://hdl.handle.net/10722/452632006-01-01T00:00:00Z
- Phase diagram of an extended Kondo lattice model for manganites: The Schwinger-boson mean-field approachhttp://hdl.handle.net/10722/43289Title: Phase diagram of an extended Kondo lattice model for manganites: The Schwinger-boson mean-field approach
Authors: Gu, RY; Wang, ZD; Shen, SQ; Xing, DY
Abstract: We investigate the phase diagram of an extended Kondo lattice model for doped manganese oxides in the presence of strong but finite Hund's coupling and on-site Coulomb interaction. By means of the Schwinger-boson mean-field approach, it is found that, besides magnetic ordering, there will be nonuniform charge distributions, such as charge ordering and phase separation, if the interaction between electrons prevails over the hybridization. Which of the charge ordering and phase separation appears is determined by a competition between effective repulsive and attractive interactions due to virtual processes of electron hopping. Calculated results show that strong electron correlations caused by the on-site Coulomb interaction as well as the finite Hund's coupling play an important role in the magnetic ordering and charge distribution at low temperatures. ©2000 The American Physical Society.
Sat, 01 Jan 2000 00:00:00 GMThttp://hdl.handle.net/10722/432892000-01-01T00:00:00Z
- Berry phase and its induced charge and spin currents in a ring of a double-exchange systemhttp://hdl.handle.net/10722/43276Title: Berry phase and its induced charge and spin currents in a ring of a double-exchange system
Authors: Liang, SD; Shen, SQ; Wang, ZD
Abstract: A ring of double-exchange system is investigated to explore the Berry phase acquired by the interplay of localized and conduction electrons. The competition between the double-exchange ferromagnetism and the superexchange antiferromagnetic coupling from the localized electrons leads to a phase transition from a ferromagnetic state to a spin spiral state. The spin spiral state acquires a nonzero Berry phase along the ring, and induces both charge and spin currents simultaneously. It is predicted that both the Aharonov-Bohm effect and Aharonov-Cashier effect will be exhibited spontaneously in the system. © 1999 The American Physical Society.
Fri, 01 Jan 1999 00:00:00 GMThttp://hdl.handle.net/10722/432761999-01-01T00:00:00Z
- Massive Dirac fermions and spin physics in an ultrathin film of topological insulatorhttp://hdl.handle.net/10722/123861Title: Massive Dirac fermions and spin physics in an ultrathin film of topological insulator
Authors: Lu, HZ; Shan, WY; Yao, W; Niu, Q; Shen, SQ
Abstract: We study transport and optical properties of the surface states, which lie in the bulk energy gap of a thin-film topological insulator. When the film thickness is comparable with the surface-state decay length into the bulk, the tunneling between the top and bottom surfaces opens an energy gap and form two degenerate massive Dirac hyperbolas. Spin-dependent physics emerges in the surface bands, which are vastly different from the bulk behavior. These include the surface spin Hall effects, spin-dependent orbital magnetic moment, and spin-dependent optical transition selection rule, which allows optical spin injection. We show a topological quantum phase transition where the Chern number of the surface bands changes when varying the thickness of the thin film. © 2010 The American Physical Society.
Fri, 01 Jan 2010 00:00:00 GMThttp://hdl.handle.net/10722/1238612010-01-01T00:00:00Z
- Spin Hall effect and Berry phase in two-dimensional electron gashttp://hdl.handle.net/10722/43456Title: Spin Hall effect and Berry phase in two-dimensional electron gas
Authors: Shen, SQ
Abstract: The spin Hall effect is investigated in a high mobility two-dimensional electron system with the spin-orbital coupling of both the Rashba and the Dresselhaus types. A spin current perpendicular to the electric field is generated by either the Rashba or the Dresselhaus coupling. The spin Hall conductance is dependent of the stength of the coupling, but its sign is determined by the relative ratio of the two couplings. The direction of dimensional plane via adjusting the Rashba coupling. It is observed that the spin hall conductance has a close relation to the Berry phase of conduction elections.
Thu, 01 Jan 2004 00:00:00 GMThttp://hdl.handle.net/10722/434562004-01-01T00:00:00Z
- Coulomb interaction in the spin Hall effecthttp://hdl.handle.net/10722/43416Title: Coulomb interaction in the spin Hall effect
Authors: Hu, L; Gao, J; Shen, SQ
Abstract: The influence of the electronic Coulomb interaction on the spin-orbit-coupling induced spin Hall effect was discussed. It was shown that the electronic Coulomb interaction may decrease substantially the spin-orbit-coupling induced transverse spin accumulation in a sample when a longitudinal charge current circulates in it, and the decrease of the transverse spin accumulation due to the influences of the Coulomb interaction is determined by the ratio of the spin-drag resistivity to the ordinary resistivity of the sample.
Wed, 01 Jan 2003 00:00:00 GMThttp://hdl.handle.net/10722/434162003-01-01T00:00:00Z
- Antiferromagnetism and phase separation in electronic models for doped transition-metal oxideshttp://hdl.handle.net/10722/43236Title: Antiferromagnetism and phase separation in electronic models for doped transition-metal oxides
Authors: Shen, SQ; Wang, ZD
Abstract: We investigate the ground state properties of electronic models for doped transition-metal oxides. An effective t-J like Hamiltonian is derived from the case of strong Hund coupling between the conduction electrons and localized spins by means of the projection technique. An attractive interaction for conduction electrons and an antiferromagnetic coupling of the localized spin are obtained. A large ratio of the attraction to effective electron hopping, which is modulated by the spin background, will lead to the phase separation. The antiferromagnetic phase and the phase separation appear in the case of either high or low density of electrons. The possible relevance of the phase separation to the charge stripe phase in doped transition-metal oxides is dicussed.
Thu, 01 Jan 1998 00:00:00 GMThttp://hdl.handle.net/10722/432361998-01-01T00:00:00Z
- Controllable quantum spin precession by Aharonov-Casher phase in a conducting ringhttp://hdl.handle.net/10722/42492Title: Controllable quantum spin precession by Aharonov-Casher phase in a conducting ring
Authors: Shen, SQ; Li, ZJ; Ma, Z
Abstract: A connection between the quantum spin polarization orientation and spin precession in quantum transport in an AC ring was established. It was shown that spin precession can be controlled through the external electric field by means of the AC effect. An exact solution for the problem and focus on the spin aspect of quantum transport was developed.
Thu, 01 Jan 2004 00:00:00 GMThttp://hdl.handle.net/10722/424922004-01-01T00:00:00Z
- Nonexponential relaxation and quantum tunnel splitting in the molecular magnet Fe8http://hdl.handle.net/10722/43373Title: Nonexponential relaxation and quantum tunnel splitting in the molecular magnet Fe8
Authors: Chen, ZD; Shen, SQ
Abstract: Magnetic relaxation in molecular magnets under a sweeping field is studied by taking into account local stray fields. It is found that the randomness of local stray field leads to a distribution of the relaxation rate which subsequently makes the relaxation deviate from the exponential law as predicted by the Landau-Zener model such that the Landau-Zener method needs to be revised to deduce an exact tunneling splitting. The tunneling splitting and distribution width of local stray fields are derived from the experimental data for molecular magnets Fe8.
Wed, 01 Jan 2003 00:00:00 GMThttp://hdl.handle.net/10722/433732003-01-01T00:00:00Z
- Spin and orbital excitations in undoped manganiteshttp://hdl.handle.net/10722/42458Title: Spin and orbital excitations in undoped manganites
Authors: Gu, RY; Shen, SQ; Wang, ZD; Xing, DY
Abstract: We develop a theory for spin and orbital excitations in undoped manganites to account for the spin and orbital orderings observed experimentally. It is found that the anisotropy of the magnetic structure is closely related to the orbital ordering, and the Jahn-Teller effect stabilizes the orbital ordering. The phase diagram and the low-energy excitation spectra for both spin and orbital orderings are obtained. The calculated critical temperatures can be quantitatively comparable to the experimental data. © 2000 American Institute of Physics.
Sat, 01 Jan 2000 00:00:00 GMThttp://hdl.handle.net/10722/424582000-01-01T00:00:00Z
- Spin relaxation in submonolayer and monolayer InAs structures grown in a GaAs matrixhttp://hdl.handle.net/10722/59618Title: Spin relaxation in submonolayer and monolayer InAs structures grown in a GaAs matrix
Authors: Yang, C; Cui, X; Shen, SQ; Xu, Z; Ge, W
Abstract: Electron-spin dynamics in InAs/GaAs heterostructures consisting of a single layer of InAs (1/3-1 monolayer) embedded in (001) and (311)A GaAs matrix was studied by means of time-resolved Kerr rotation spectroscopy. The spin-relaxation time of the submonolayer InAs samples is significantly enhanced, compared with that of the monolayer InAs sample. The electron-spin-relaxation time and the effective g factor in submonolayer samples were found to be strongly dependent on the photogenerated carrier density. The contribution from both the D'yakonov-Perel' mechanism and Bir-Aronov-Pikus mechanism are discussed to interpret the temperature dependence of spin decoherence at various carrier densities. © 2009 The American Physical Society.
Thu, 01 Jan 2009 00:00:00 GMThttp://hdl.handle.net/10722/596182009-01-01T00:00:00Z
- Current-induced effect on the resistivity of epitaxial thin films of La 0.7Ca 0.3MnO 3 and La 0.85Ba 0.15MnO 3http://hdl.handle.net/10722/42483Title: Current-induced effect on the resistivity of epitaxial thin films of La 0.7Ca 0.3MnO 3 and La 0.85Ba 0.15MnO 3
Authors: Gao, J; Shen, SQ; Li, TK; Sun, JR
Abstract: A study was performed on the current-induced effect on the resistivity of epitaxial thin films of La 0.7Ca 0.3MnO 3 and La 0.85Ba 0.15MnO 3. The peak resistance showed a significant change at different current or current resistance. It was found that for both the compounds the dependence of the measured resistance on current revealed a good linear relationship.
Wed, 01 Jan 2003 00:00:00 GMThttp://hdl.handle.net/10722/424832003-01-01T00:00:00Z
- Calculation of tunnel splitting in a biaxial spin particle with an applied magnetic fieldhttp://hdl.handle.net/10722/48658Title: Calculation of tunnel splitting in a biaxial spin particle with an applied magnetic field
Authors: Zhou, B; Shen, SQ; Liang, JQ
Abstract: The level splitting formulae of excited states as well as ground state for a biaxial spin particle in the presence of an applied magnetic field are obtained in a simple way from Schrödinger theory. Considering the boundary condition of the wave function, we obtain the tunneling splitting of the energy levels for half-integral spins as well as for the integral spins. The results obtained are compared with those previously derived by complicated pseudoparticle methods and numerical calculation values.
Thu, 01 Jan 2004 00:00:00 GMThttp://hdl.handle.net/10722/486582004-01-01T00:00:00Z
- Dynamics and Berry phase of two-species Bose-Einstein condensateshttp://hdl.handle.net/10722/43422Title: Dynamics and Berry phase of two-species Bose-Einstein condensates
Authors: Chen, ZD; Liang, JQ; Shen, SQ; Xie, WF
Abstract: A full quantum-mechanical evaluation of the dynamics of the two-species Bose-Einstein condensates was reported. Phenomenon of self-trapping, phase locking and collapse-revival were also investigated. The Berry phase which depends upon the number parity of atoms was found out. Results show that the nonlinear interatom coupling does not affect the Berry phase but leads to damping and collapse revival.
Thu, 01 Jan 2004 00:00:00 GMThttp://hdl.handle.net/10722/434222004-01-01T00:00:00Z
- Effective Hamiltonian for an extended Kondo-lattice model and a possible origin of charge ordering in half-doped manganiteshttp://hdl.handle.net/10722/43265Title: Effective Hamiltonian for an extended Kondo-lattice model and a possible origin of charge ordering in half-doped manganites
Authors: Shen, SQ; Wang, ZD
Abstract: An effective Hamiltonian is derived in the case of the strong Hund coupling and on-site Coulomb interaction by means of a projective perturbation approach. A physical mechanism for charge ordering in half-doped manganites (R 0.5X 0.5MnO 3) is proposed. The virtual process of electron hopping results in antiferromagnetic superexchange and a repulsive interaction, which may drive electrons to form a Wigner lattice. The phase diagram of the ground state of the model is presented at half doping. In the case of formation of a Wigner lattice, we prove that spins of electrons are aligned ferromagnetically as well as that the localized spin background is antiferromagnetic. The influence of the on-site Coulomb interaction is also discussed. © 1999 The American Physical Society.
Fri, 01 Jan 1999 00:00:00 GMThttp://hdl.handle.net/10722/432651999-01-01T00:00:00Z