HKU Scholars Hubhttp://hub.hku.hkThe DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material.Thu, 13 Dec 2018 03:26:05 GMT2018-12-13T03:26:05Z502151- Theory of superconductivity in a three-orbital model of Sr2RuO4http://hdl.handle.net/10722/193902Title: Theory of superconductivity in a three-orbital model of Sr2RuO4
Authors: Wang, QH; Platt, C; Yang, Y; Honerkamp, C; Zhang, F; Hanke, W; Rice, TM; Thomale, R
Tue, 01 Jan 2013 00:00:00 GMThttp://hdl.handle.net/10722/1939022013-01-01T00:00:00Z
- Origin of the checkerboard pattern in scanning tunneling microscopy maps of underdoped cuprate superconductorshttp://hdl.handle.net/10722/80559Title: Origin of the checkerboard pattern in scanning tunneling microscopy maps of underdoped cuprate superconductors
Authors: Yang, KY; Chen, WQ; Rice, TM; Zhang, FC
Abstract: The checkerboard pattern in the differential conductance maps on underdoped cuprates appears when the scanning tunneling microscopy is placed above the O sites in the outermost CuO2 plane. In this position the interference between tunneling paths through the apical ions above the neighboring Cu sites leads to an asymmetric weighting of final states in the two antinodal regions of k space. The form of the asymmetry in the differential conductance spectra in the checkerboard pattern favors asymmetry in the localization length rather than a nematic displacement as the underlying origin. © 2009 The American Physical Society.
Thu, 01 Jan 2009 00:00:00 GMThttp://hdl.handle.net/10722/805592009-01-01T00:00:00Z
- 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
- Controllable nonlocal transport of Majorana fermions with the aid of two quantum dotshttp://hdl.handle.net/10722/203316Title: Controllable nonlocal transport of Majorana fermions with the aid of two quantum dots
Authors: Liu, J; Wang, J; Zhang, F
Wed, 01 Jan 2014 00:00:00 GMThttp://hdl.handle.net/10722/2033162014-01-01T00:00:00Z
- Flat band electrons and interactions in rhombohedral trilayer graphenehttp://hdl.handle.net/10722/186184Title: Flat band electrons and interactions in rhombohedral trilayer graphene
Authors: Wang, H; Gao, J; Zhang, F
Tue, 01 Jan 2013 00:00:00 GMThttp://hdl.handle.net/10722/1861842013-01-01T00:00:00Z
- Layer antiferromagnetic state in bilayer graphene: A first-principles investigationhttp://hdl.handle.net/10722/184653Title: Layer antiferromagnetic state in bilayer graphene: A first-principles investigation
Authors: Wang, Y; Wang, H; Gao, J; Zhang, F
Tue, 01 Jan 2013 00:00:00 GMThttp://hdl.handle.net/10722/1846532013-01-01T00:00:00Z
- Vortex structures in model p-wave superconducting Sr2RuO4: Single two-dimensional band vs quasi-one-dimensional bandshttp://hdl.handle.net/10722/183153Title: Vortex structures in model p-wave superconducting Sr2RuO4: Single two-dimensional band vs quasi-one-dimensional bands
Authors: Huo, J; Zhang, F
Tue, 01 Jan 2013 00:00:00 GMThttp://hdl.handle.net/10722/1831532013-01-01T00:00:00Z
- Spin Density Wave Fluctuations and p-Wave Pairing in Sr2RuO4http://hdl.handle.net/10722/186178Title: Spin Density Wave Fluctuations and p-Wave Pairing in Sr2RuO4
Authors: HUO, J; Rice, TM; Zhang, F
Tue, 01 Jan 2013 00:00:00 GMThttp://hdl.handle.net/10722/1861782013-01-01T00:00:00Z
- Influence of Quantum and Thermal Noise on Spin-Torque-Driven Magnetization Switchinghttp://hdl.handle.net/10722/186151Title: Influence of Quantum and Thermal Noise on Spin-Torque-Driven Magnetization Switching
Authors: Wang, Y; Zhou, Y; Zhang, F
Tue, 01 Jan 2013 00:00:00 GMThttp://hdl.handle.net/10722/1861512013-01-01T00:00:00Z
- Spin-orbital entanglement and quantum phase transitions in a spin-orbital chain with SU (2) ×sU (2) symmetryhttp://hdl.handle.net/10722/92108Title: Spin-orbital entanglement and quantum phase transitions in a spin-orbital chain with SU (2) ×sU (2) symmetry
Authors: Chen, Y; Wang, ZD; Li, YQ; Zhang, FC
Abstract: Spin-orbital entanglement in quantum spin-orbital systems is quantified by a specifically reduced von Neumann entropy and is calculated for the ground state of a coupled spin-orbital chain with SU (2) ×SU (2) symmetry. By analyzing the discontinuity and local extreme of the reduced entropy, we deduce a rich phase diagram describing quantum phase transitions in this system with complex correlations between multiple degrees of freedom. © 2007 The American Physical Society.
Mon, 01 Jan 2007 00:00:00 GMThttp://hdl.handle.net/10722/921082007-01-01T00:00:00Z
- 0-π transition characteristic of the Josephson current in a carbon nanotube quantum dothttp://hdl.handle.net/10722/203323Title: 0-π transition characteristic of the Josephson current in a carbon nanotube quantum dot
Authors: Li, L; Zheng, BB; Chen, W; Chen, H; Luo, HG; Zhang, F
Wed, 01 Jan 2014 00:00:00 GMThttp://hdl.handle.net/10722/2033232014-01-01T00:00:00Z
- Edge superconducting correlation in the attractive-U Kane-Mele-Hubbard modelhttp://hdl.handle.net/10722/175219Title: Edge superconducting correlation in the attractive-U Kane-Mele-Hubbard model
Authors: Yuan, J; Gao, JH; Chen, WQ; Ye, F; Zhou, Y; Zhang, FC
Abstract: The two-dimensional Kane-Mele model with attractive Hubbard interaction U is studied by using a self-consistent mean-field theory. At U=0, the ground state is a topological insulator. At U larger than a critical value U c, the ground state is a bulk superconductor. At 0<U<U c, the bulk remains insulating while the edge state shows superconducting correlation. The effective model for the edge superconducting state is discussed. © 2012 American Physical Society.
Sun, 01 Jan 2012 00:00:00 GMThttp://hdl.handle.net/10722/1752192012-01-01T00:00:00Z
- Fractional quantum Hall states in two-dimensional electron systems with anisotropic interactionshttp://hdl.handle.net/10722/159794Title: Fractional quantum Hall states in two-dimensional electron systems with anisotropic interactions
Authors: Wang, H; Narayanan, R; Wan, X; Zhang, F
Abstract: We study the anisotropic effect of the Coulomb interaction on a 1/3-filling fractional quantum Hall system by using an exact diagonalization method on small systems in torus geometry. For weak anisotropy the system remains to be an incompressible quantum liquid, although anisotropy manifests itself in density correlation functions and excitation spectra. When the strength of anisotropy increases, we find the system develops a Hall-smectic-like phase with a one-dimensional charge density wave order and is unstable towards the one-dimensional crystal in the strong anisotropy limit. In all three phases of the Laughlin liquid, Hall-smectic-like, and crystal phases the ground state of the anisotropic Coulomb system can be well described by a family of model wave functions generated by an anisotropic projection Hamiltonian. We discuss the relevance of the results to the geometrical description of fractional quantum Hall states proposed by Haldane. © 2012 American Physical Society.
Sun, 01 Jan 2012 00:00:00 GMThttp://hdl.handle.net/10722/1597942012-01-01T00:00:00Z
- Dipolar dynamics for interacting ultracold fermions in a trapped optical latticehttp://hdl.handle.net/10722/177371Title: Dipolar dynamics for interacting ultracold fermions in a trapped optical lattice
Authors: Huo, J; Chen, W; Schollwock, U; Troyer, M; Zhang, F
Sun, 01 Jan 2012 00:00:00 GMThttp://hdl.handle.net/10722/1773712012-01-01T00:00:00Z
- Exploring quantum phase transitions with a sublattice entanglement scenariohttp://hdl.handle.net/10722/92314Title: Exploring quantum phase transitions with a sublattice entanglement scenario
Authors: Chen, Y; Wang, ZD; Zhang, FC
Abstract: We introduce a measure called reduced entropy of sublattice to quantify entanglement in spin, electron, and boson systems. By analyzing this quantity, we reveal an intriguing connection between quantum entanglement and quantum phase transitions in various strongly correlated systems: the local extremes of reduced entropy and its first derivative as functions of the coupling constant coincide, respectively, with the first and second order transition points. Exact numerical studies merely for small lattices reproduce several well-known results, demonstrating that our scenario is quite promising for exploring quantum phase transitions. © 2006 The American Physical Society.
Sun, 01 Jan 2006 00:00:00 GMThttp://hdl.handle.net/10722/923142006-01-01T00:00:00Z
- 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
- Resonant intrinsic spin hall effect in p-type GaAs quantum well structurehttp://hdl.handle.net/10722/146333Title: Resonant intrinsic spin hall effect in p-type GaAs quantum well structure
Authors: Dai, X; Fang, Z; Yao, YG; Zhang, FC
Abstract: We study intrinsic spin Hall effect in p-type GaAs quantum well structure described by Luttinger Hamiltonian and a Rashba spin-orbit coupling arising from the structural inversion symmetry breaking. The Rashba term induces an energy level crossing in the lowest heavy hole subband, which gives rise to a resonant spin Hall conductance. The resonance may be used to identify the intrinsic spin Hall effect in experiments. © 2006 The American Physical Society.
Sun, 01 Jan 2006 00:00:00 GMThttp://hdl.handle.net/10722/1463332006-01-01T00:00:00Z
- Gossamer superconductivity near antiferromagnetic mott insulator in layered organic conductorshttp://hdl.handle.net/10722/42503Title: Gossamer superconductivity near antiferromagnetic mott insulator in layered organic conductors
Authors: Gan, JY; Chen, Y; Su, ZB; Zhang, FC
Abstract: Layered organic superconductors are on the verge of the Mott insulator. We use the Gutzwiller variational method to study a two-dimensional Hubbard model including a spin exchange coupling term as a minimal model for the compounds. The ground state is found to be a Gossamer superconductor at small on-site Coulomb repulsion U and an antiferromagnetic Mott insulator at large U, separated by a first order phase transition. Our theory is qualitatively consistent with major experiments reported in organic superconductors. © 2005 The American Physical Society.
Sat, 01 Jan 2005 00:00:00 GMThttp://hdl.handle.net/10722/425032005-01-01T00:00:00Z
- Global phase diagram of three-dimensional extended Boson Hubbard model: A continuous-time quantum Monte Carlo studyhttp://hdl.handle.net/10722/139659Title: Global phase diagram of three-dimensional extended Boson Hubbard model: A continuous-time quantum Monte Carlo study
Authors: Xi, B; Ye, F; Chen, W; Zhang, F; Su, G
Abstract: We present the global phase diagram of the extended boson Hubbard model on a simple cubic lattice by quantum Monte Carlo simulation with the worm update algorithm. Four kinds of phases are supported by this model, including superfluid, supersolid, Mott, and charge density wave (CDW) states, which are identified in the phase diagram of chemical potential μ versus nearest-neighbor interaction V. By changing the chemical potential, a continuous transition is found from the Mott phase to a superfluid phase without breaking the translational symmetry. For an insulating CDW state, adding particles to it gives rise to a continuous transition to a supersolid phase, while removing particles usually leads to a first-order transition to either a supersolid or superfluid phase. By tuning the nearest-neighbor interaction, one can realize the transition between two insulating phases, Mott and CDW, with the same particle density, which turns out to be first order. We also confirm the result in Phys. Rev. B 79, 094503 (2009) that a supersolid phase with average particle density less than 1/2 can exist in a small region of the μ-V phase diagram. © 2011 American Physical Society.
Sat, 01 Jan 2011 00:00:00 GMThttp://hdl.handle.net/10722/1396592011-01-01T00:00:00Z
- Field-free synthetic-ferromagnet spin torque oscillatorhttp://hdl.handle.net/10722/182181Title: Field-free synthetic-ferromagnet spin torque oscillator
Authors: Zhou, Y; Xiao, J; Bauer, GEW; Zhang, F
Tue, 01 Jan 2013 00:00:00 GMThttp://hdl.handle.net/10722/1821812013-01-01T00:00:00Z
- Zn-impurity effect and interplay of s± and s++ pairings in iron-based superconductorshttp://hdl.handle.net/10722/181707Title: Zn-impurity effect and interplay of s± and s++ pairings in iron-based superconductors
Authors: Yao, Z; Chen, W; Li, YK; Cao, GH; Jiang, H; Wang, Q; Xu, ZA; Zhang, F
Sun, 01 Jan 2012 00:00:00 GMThttp://hdl.handle.net/10722/1817072012-01-01T00:00:00Z
- Local antiferromagnetic moment induced by Zn impurity in high- Tc superconducting copper oxides: A resonating-valence-bond picturehttp://hdl.handle.net/10722/80366Title: Local antiferromagnetic moment induced by Zn impurity in high- Tc superconducting copper oxides: A resonating-valence-bond picture
Authors: Li, T; Wang, QH; Weng, ZY; Yang, F; Zhang, FC
Abstract: Based on a Gutzwiller projected BCS wave function, it is shown that a local S=1 2 moment is present around a vacancy site (zinc impurity) in a form of staggered magnetic moments, which is a direct consequence of the short-range resonating-valence-bond pairing in the spin background. © 2006 The American Physical Society.
Sun, 01 Jan 2006 00:00:00 GMThttp://hdl.handle.net/10722/803662006-01-01T00:00:00Z
- Variational Monte Carlo studies of gossamer superconductivityhttp://hdl.handle.net/10722/59627Title: Variational Monte Carlo studies of gossamer superconductivity
Authors: Guertler, S; Wang, QH; Zhang, FC
Abstract: We use a partially Gutzwiller projected BCS d-wave wave function with an antiferromagnetic-weighting
factor to study the ground-state phase diagram of a half-filled Hubbard-Heisenberg model in a square lattice with nearest-neighbor hopping t and a diagonal hopping t'. The calculations are carried out by using variational Monte Carlo method which treats the Gutzwiller projection explicitly. At large on-site Coulomb interaction U, the ground state is antiferromagnetic. As U decreases, the ground state becomes superconducting and eventually metallic. The phase diagram is obtained by extensive calculations. As compared to the strong effect of U/ t, the phase boundaries turn out to be less sensitive to t' / t. The result is consistent with the phase diagram in layered organic conductors and is compared to the earlier mean-field result based on the Gutzwiller approximation.
Thu, 01 Jan 2009 00:00:00 GMThttp://hdl.handle.net/10722/596272009-01-01T00:00:00Z
- High spin systems with orbital degeneracyhttp://hdl.handle.net/10722/42462Title: High spin systems with orbital degeneracy
Authors: Shen, SQ; Xie, XC; Zhang, FC
Abstract: A class of high spin systems with twofold orbital degeneracy was analyzed in the limits of large spin. The method was applied to study case where isotropic electron hopping integrals were present and the effects of the quantum spin fluctuations were examined using the linearized spin wave theory. It was found that orbital valence bond state was stable in a certain parameter region.
Tue, 01 Jan 2002 00:00:00 GMThttp://hdl.handle.net/10722/424622002-01-01T00:00:00Z
- Directional ordering of fluctuations in a two-dimensional compass modelhttp://hdl.handle.net/10722/42502Title: Directional ordering of fluctuations in a two-dimensional compass model
Authors: Mishra, A; Ma, M; Zhang, FC; Guertler, S; Tang, LH; Wan, S
Abstract: A classical realization of directional coupling in two dimension of the effective orbital-orbital interaction in the Mott insulating phase of the transition metal oxides (TMO) was presented. The model exhibited partial orbital ordering in the form of directional ordering of fluctuation at low temperatures stabilized by an entropy gap. The directional ordering was necessarily accompanied by a lattice distortion and the bond length in horizontal and vertical directions became unequal when the couplings of the orbital isosopin to lattice modes were included. Analysis shows that the compass model has a low temperature phase which exhibited long-ranged correlations in the directions of fluctuations in both isospin and lattice spaces.
Thu, 01 Jan 2004 00:00:00 GMThttp://hdl.handle.net/10722/425022004-01-01T00:00:00Z
- Effect of superlattice modulation of electronic parameters on the density of states of cuprate superconductorshttp://hdl.handle.net/10722/57342Title: Effect of superlattice modulation of electronic parameters on the density of states of cuprate superconductors
Authors: Yang, KY; Rice, TM; Zhang, FC
Abstract: Recent scanning tunneling microscopy on BSCCO 2212 has revealed a substantial spatial supermodulation of the energy gap in the superconducting state. We propose that this gap modulation is due to the superlattice modulations of the atoms in the structure, and hence the parameters in a microscopic model of the CuO2 plane. The gap modulation is estimated using renormalized mean field theory for a t- t′ -J model on a superlattice. The results compare well with experiment. © 2007 The American Physical Society.
Mon, 01 Jan 2007 00:00:00 GMThttp://hdl.handle.net/10722/573422007-01-01T00:00:00Z
- 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
- Self-doping effect and successive magnetic transitions in superconducting Sr2 VFeAsO3http://hdl.handle.net/10722/142470Title: Self-doping effect and successive magnetic transitions in superconducting Sr2 VFeAsO3
Authors: Cao, GH; Ma, Z; Wang, C; Sun, Y; Bao, J; Jiang, S; Luo, Y; Feng, C; Zhou, Y; Xie, Z; Hu, F; Wei, S; Nowik, I; Felner, I; Zhang, L; Xu, Z; Zhang, FC
Abstract: We have studied a quinary Fe-based superconductor Sr 2 VFeAsO 3 by the measurements of x-ray diffraction, x-ray absorption, Mössbauer spectrum, resistivity, magnetization, and specific heat. This apparently undoped oxyarsenide is shown to be self-doped via electron transfer from the V3 + ions. We observed successive magnetic transitions within the VO 2 layers: an antiferromagnetic transition at 150 K followed by a weak ferromagnetic transition at 55 K. The spin orderings within the VO 2 planes are discussed based on mixed valence of V3 + and V4 +. © 2010 The American Physical Society.
Fri, 01 Jan 2010 00:00:00 GMThttp://hdl.handle.net/10722/1424702010-01-01T00:00:00Z
- Giant mesoscopic spin hall effect on the surface of topological insulatorhttp://hdl.handle.net/10722/139611Title: Giant mesoscopic spin hall effect on the surface of topological insulator
Authors: Gao, JH; Yuan, J; Chen, WQ; Zhou, Y; Zhang, FC
Abstract: We study mesoscopic spin Hall effect on the surface of a topological insulator with a step-function potential by using the McMillan method commonly used in the study of superconductor junctions. In the ballistic transport regime, we predict a giant spin polarization induced by a transverse electric current with parameter suitable to the topological insulator thin film Bi 2Se 3. The spin polarization oscillates across the potential boundary with no confinement due to the Klein paradox, and should be observable in a spin resolved scanning tunneling microscope. © 2011 American Physical Society.
Sat, 01 Jan 2011 00:00:00 GMThttp://hdl.handle.net/10722/1396112011-01-01T00:00:00Z
- Mott insulator-superfluid transitions in a two-band model at finite temperature and possible application to supersolid He4http://hdl.handle.net/10722/57329Title: Mott insulator-superfluid transitions in a two-band model at finite temperature and possible application to supersolid He4
Authors: Zhuang, HB; Ma, M; Dai, X; Zhang, FC
Abstract: We study the Mott insulator-superfluid transition in a two-band boson Hubbard model, which can be mapped onto a spin- 1 2 XY model with spins coupled to an additional Ising degree of freedom. By using a modified mean field theory that includes the effects of phase fluctuations, we show that the transition is first order at both zero and finite temperatures. On the Mott insulator side, there may be reentrance in phase transition. These features are consequences of the underlying transition between competing defect poor and defect rich phases. The possible relevance of the model and our results to supersolid He4 and cold bosonic atoms in optical lattices are discussed. © 2007 The American Physical Society.
Mon, 01 Jan 2007 00:00:00 GMThttp://hdl.handle.net/10722/573292007-01-01T00:00:00Z
- Anderson impurity in a helical metalhttp://hdl.handle.net/10722/123854Title: Anderson impurity in a helical metal
Authors: Feng, XY; Chen, WQ; Gao, JH; Wang, QH; Zhang, FC
Abstract: We use a trial wave function to study the spin-1/2 Kondo effect of a helical metal on the surface of a three-dimensional topological insulator. While the impurity spin is quenched by conduction electrons, the spin-spin correlation of the conduction electron and impurity is strongly anisotropic in both spin and spatial spaces. As a result of strong spin-orbit coupling, the out-of-plane component of the impurity spin is found to be fully screened by the orbital angular momentum of the conduction electrons. © 2010 The American Physical Society.
Fri, 01 Jan 2010 00:00:00 GMThttp://hdl.handle.net/10722/1238542010-01-01T00:00:00Z
- Quasiparticles in the pseudogap phase of underdoped cupratehttp://hdl.handle.net/10722/59657Title: Quasiparticles in the pseudogap phase of underdoped cuprate
Authors: Yang, KY; Yang, HB; Johnson, PD; Rice, TM; Zhang, FC
Abstract: Recent angle-resolved photoemission (Yang H.-B. et al., Nature, 456 (2008) 77) and scanning tunneling microscopy (Kohsaka Y. et al., Nature, 454 (2008) 1072) measurements on underdoped cuprates have yielded new spectroscopic information on quasiparticles in the pseudogap phase. New features of the normal state such as particle-hole asymmetry, maxima in the energy dispersion, and accompanying drops in the spectral weight of quasiparticles agree with the ansatz of Yang et al. for the single-particle propagator in the pseudogap phase. The coherent quasiparticle dispersion and reduced asymmetry in the tunneling density of states in the superconducting state can also be described by this propagator. © EPLA, 2009.
Thu, 01 Jan 2009 00:00:00 GMThttp://hdl.handle.net/10722/596572009-01-01T00:00:00Z
- Electronic structure near an impurity and terrace on the surface of a three-dimensional topological insulatorhttp://hdl.handle.net/10722/81079Title: Electronic structure near an impurity and terrace on the surface of a three-dimensional topological insulator
Authors: Wang, QH; Wang, D; Zhang, FC
Abstract: Motivated by recent scanning tunneling microscopy experiments on surfaces of Bi1-x Sb x′ and Bi2 Te3, we theoretically study the electronic structure of a three-dimensional (3D) topological insulator in the presence of a local impurity or a domain wall on its surface using a 3D lattice model. While the local density of states (LDOS) oscillates significantly in space at energies above the bulk gap, the oscillation due to the in-gap surface Dirac fermions is very weak. The extracted modulation wave number as a function of energy satisfies the Dirac dispersion for in-gap energies and follows the border of the bulk continuum above the bulk gap. We have also examined analytically the effects of the defects by using a pure Dirac fermion model for the surface states and found that the LDOS decays asymptotically faster at least by a factor of 1/r than that in normal metals, consistent with the results obtained from our lattice model. © 2010 The American Physical Society.
Fri, 01 Jan 2010 00:00:00 GMThttp://hdl.handle.net/10722/810792010-01-01T00:00:00Z
- Dynamically generated dimension reduction and crossover in a spin-orbital modelhttp://hdl.handle.net/10722/43445Title: Dynamically generated dimension reduction and crossover in a spin-orbital model
Authors: De Silva, TN; Ma, M; Zhang, FC
Abstract: We study a spin-orbital model in which the spin-spin interaction couples linearly to the orbital isospin. Fluctuations drive the transition from a paramagnetic state to a C-type-ordered state into a strongly first-order one, as observed in V2O3. At T=O, there is a ferro-orbital-C-spin to ferro-orbital-G-spin transition. Close to the transition point, the system shows dynamically generated dimension reduction and crossover, resulting in one or more spin reentrant transitions.
Thu, 01 Jan 2004 00:00:00 GMThttp://hdl.handle.net/10722/434452004-01-01T00:00:00Z
- Disorder effect of resonant spin Hall effect in a tilted magnetic fieldhttp://hdl.handle.net/10722/81068Title: Disorder effect of resonant spin Hall effect in a tilted magnetic field
Authors: Jiang, ZF; Shen, SQ; Zhang, FC
Abstract: We study the disorder effect of resonant spin Hall effect in a two-dimensional electron system with Rashba coupling in the presence of a tilted magnetic field. The competition between the Rashba coupling and the Zeeman coupling leads to the energy crossing of the Landau levels, which gives rise to the resonant spin Hall effect. Utilizing the Streda's formula within the self-consistent Born approximation, we find that the impurity scattering broadens the energy levels and the resonant spin Hall conductance exhibits a double peak around the resonant point, which is recovered in an applied tilted magnetic field. © 2009 The American Physical Society.
Thu, 01 Jan 2009 00:00:00 GMThttp://hdl.handle.net/10722/810682009-01-01T00:00:00Z
- π Junction to probe antiphase s-Wave pairing in iron pnictide superconductorshttp://hdl.handle.net/10722/81056Title: π Junction to probe antiphase s-Wave pairing in iron pnictide superconductors
Authors: Chen, WQ; Ma, F; Lu, ZY; Zhang, FC
Abstract: Josephson junctions between a FeAs-based superconductor with antiphase s-wave pairing and a conventional s-wave superconductor are studied. The translational invariance in a planar junction between a single crystal pnictide and an aluminum metal greatly enhances the relative weight of electron pockets in the pnictide to the critical current. In a wide doping region of the pnictide, a planar and a point contact junction have opposite phases, which can be used to design a trijunction ring with π phase to probe the antiphase pairing. © 2009 The American Physical Society.
Thu, 01 Jan 2009 00:00:00 GMThttp://hdl.handle.net/10722/810562009-01-01T00:00:00Z
- Finite-temperature Gutzwiller projection for strongly correlated electron systemshttp://hdl.handle.net/10722/125278Title: Finite-temperature Gutzwiller projection for strongly correlated electron systems
Authors: Wang, WS; He, XM; Wang, D; Wang, QH; Wang, ZD; Zhang, FC
Abstract: We generalized the Gutzwiller projectional variational method for the ground state of strongly correlated electron systems to the case of finite temperature. Under the Gutzwiller approximation, we show that this maps to a finite temperature renormalized mean-field theory. As one of the key ingredients in the theory, we obtained an explicit expression of the projection entropy or the entropy change due to the projection. We illustrate the application of the theory to the Anderson impurity problem and the half-filled Hubbard model and compare the theory to more elaborate techniques. We find qualitative agreement. The theory can be applied to a wide variety of Hubbard, t-J, and Anderson impurity models. © 2010 The American Physical Society.
Fri, 01 Jan 2010 00:00:00 GMThttp://hdl.handle.net/10722/1252782010-01-01T00:00:00Z
- Fermi surface nesting and spin density wave instability in the overdoped superconducting iron pnictideshttp://hdl.handle.net/10722/225567Title: Fermi surface nesting and spin density wave instability in the overdoped superconducting iron pnictides
Authors: Jiang, HM; Yao, ZJ; Zhang, FC
Abstract: The nesting of electron Fermi pocket with one of the two hole pockets around the Brillouin zone center has been attributed to the spin density wave (SDW) instability in the parent compound of superconducting iron pnictides. We propose here that the second hole Fermi pocket may be nested with the electron pocket in the doped case, which results in a new SDW instability. Our work is motivated by and may explain the recent scanning tunneling spectroscopy (STM) measurements on NaFe1−xCoxAs, which show an asymmetric gap-like feature near the Fermi level in the overdoped regime (Zhou X. et al., Phys. Rev. Lett., 109 (2012) 037002). We use a multi-band model to examine this feature within random phase approximation to include the coupling between the itinerant electron and the local spins.
Sun, 01 Jan 2012 00:00:00 GMThttp://hdl.handle.net/10722/2255672012-01-01T00:00:00Z
- Localized in-gap states and quantum spin Hall effect in Si-doped InAs/GaSb quantum wellshttp://hdl.handle.net/10722/200801Title: Localized in-gap states and quantum spin Hall effect in Si-doped InAs/GaSb quantum wells
Authors: Xu, DH; Gao, J; Liu, CX; Sun, JH; Zhang, F; Zhou, Y
Wed, 01 Jan 2014 00:00:00 GMThttp://hdl.handle.net/10722/2008012014-01-01T00:00:00Z
- Theory for charge and orbital density-wave states in manganite La0.5Sr1.5MnO4http://hdl.handle.net/10722/183152Title: Theory for charge and orbital density-wave states in manganite La0.5Sr1.5MnO4
Authors: Yao, Z; Chen, W; Gao, J; Jiang, H; Zhang, F
Tue, 01 Jan 2013 00:00:00 GMThttp://hdl.handle.net/10722/1831522013-01-01T00:00:00Z
- Field-induced p-wave superconducting state of mesoscopic systemshttp://hdl.handle.net/10722/152812Title: Field-induced p-wave superconducting state of mesoscopic systems
Authors: Huo, JW; Chen, WQ; Raghu, S; Zhang, FC
Abstract: By using Bogoliubov-de Gennes equations, we study superconducting (SC) states in a quasi-two-dimensional system of radius R. It is shown that no vortices exist in s-wave SC samples with R<R c∼ξ(0), the T=0 coherence length. We predict that chiral p-wave states exhibit superconductivity for R<R c only in the presence of a vortex with opposite chirality. This induced SC phase is a consequence of nonzero chirality of the pairing order parameter and implies the presence of chiral edge currents. Our study may be applied to sharply probing the pairing symmetry of unconventional superconductors. © 2012 American Physical Society.
Sun, 01 Jan 2012 00:00:00 GMThttp://hdl.handle.net/10722/1528122012-01-01T00:00:00Z
- Strong coupling theory for superconducting iron pnictideshttp://hdl.handle.net/10722/59619Title: Strong coupling theory for superconducting iron pnictides
Authors: Chen, WQ; Yang, KY; Zhou, Y; Zhang, FC
Abstract: Superconductivity in iron pnictides is studied by using a two-orbital Hubbard model in the large U limit. The Coulomb repulsion induces an orbital-dependent pairing between charge carriers. The pairing is found mainly from the scattering within the same Fermi pocket. The interpocket pair scatterings determine the symmetry of the superconductivity, which is extended s wave at small Hund's coupling, and d wave at large Hund's coupling and large U. The former is consistent with recent experiments of angle-resolved photoemission spectroscopy and Andreev reflection spectroscopy. © 2009 The American Physical Society.
Thu, 01 Jan 2009 00:00:00 GMThttp://hdl.handle.net/10722/596192009-01-01T00:00:00Z
- Increase in perpendicular coercivity of Co-Ni ferrite-plated films by Zn ferrite underlayershttp://hdl.handle.net/10722/174848Title: Increase in perpendicular coercivity of Co-Ni ferrite-plated films by Zn ferrite underlayers
Authors: Kitamoto, Y; Zhang, F; Abe, M; Naoe, M
Abstract: The present article explains that Co-Ni ferrite-plated films with perpendicular coercivity H c⊥ of 3.8 kOe were obtained using Zn ferrite underlayers at the substrate temperature of 90°C without postannealing. Though a thinner recording layer is required for low noise media, perpendicular anisotropy of Co-Ni ferrite single-layer films of 50 nm in thickness is weak due to worse crystallinity in the initial growth region. Their reproduced waveforms were single pulses, as observed in the longitudinal recording media. Thus, the underlayers of a spinel type of Zn ferrite were used to improve the crystallinity in the Co-Ni ferrite layers, in particular, in the initial growth region. The thickness of the Co-Ni ferrite layer t CoNi was 50 nm, and that of the Zn ferrite underlayers t Zn was in the range of 25-110 nm. While H c⊥ of the Co-Ni ferrite single layers with t CoNi of 50 nm was 2.5 kOe, H c⊥ of the double-layer films increased with increasing t Zn, reaching 3.8 kOe at t Zn of 110 nm. The reproduced waveforms exhibited dipulses that are typical in the perpendicular recording media. These results will open the way to develop the perpendicular recording disks with high H c⊥ using plastic substrates at low temperature. © 2000 American Institute of Physics.
Sat, 01 Jan 2000 00:00:00 GMThttp://hdl.handle.net/10722/1748482000-01-01T00:00:00Z
- Effect of Ni addition into Co ferrite thin films for perpendicular recording mediahttp://hdl.handle.net/10722/174857Title: Effect of Ni addition into Co ferrite thin films for perpendicular recording media
Authors: Zhang, F; Kitamoto, Y; Abe, M; Naoe, M
Abstract: The present article describes effects of doping Ni 2+ ions into Co ferrite plated films on film structure, magnetic properties, and read/write characteristics. While thinner films are required for low noise level even in perpendicular recording media, average surface roughness R a of the Co ferrite films increased from 4 to 6 nm with decreasing the film thickness from 100 to 50 nm. Adding Ni 2+ ions had an effect on controlling the grain growth, resulting in a reduction in R a to 3-4 nm for the 50-nm-thick films by adding a small amount of Ni 2+ ions {r m[=C Ni/(C Co+C Ni)]=0.1}. Perpendicular coercivity H c⊥ of the Co-Ni ferrite film at r m=0.1 was 2500 Oe, which is almost the same as that of the Co ferrite films, and H c⊥ decreased with increasing r m. Atomic force microscope images showed that the Co-Ni ferrite films were composed of uniform and isolated grains without coagulation. As a result, a Co-Ni ferrite medium fabricated at r m=0.1 exhibited lower noise level than a Co ferrite medium without Ni addition. © 2000 American Institute of Physics.
Sat, 01 Jan 2000 00:00:00 GMThttp://hdl.handle.net/10722/1748572000-01-01T00:00:00Z
- Theory for phase transitions in insulating V 2O 3http://hdl.handle.net/10722/174815Title: Theory for phase transitions in insulating V 2O 3
Authors: Joshi, A; Ma, M; Zhang, FC
Abstract: The analysis of proposed S = 2 bond model with orbital degrees of freedom for insulating V 2O 3 was presented. It was found that the model explains magnetic ordering and other properties of magnetic phase transition. It explains occurance of magnetic and orbital ordering at same transition temperature, explains transition being first order, and observation of relatively broad peak in susceptibility for wave vector of AS ordering by neutron scattering above transition temperature.
Mon, 01 Jan 2001 00:00:00 GMThttp://hdl.handle.net/10722/1748152001-01-01T00:00:00Z
- Plaquette ordering in SU(4) antiferromagnetshttp://hdl.handle.net/10722/174828Title: Plaquette ordering in SU(4) antiferromagnets
Authors: Mishra, A; Ma, M; Zhang, FC
Abstract: We use fermion mean-field theory to study possible plaquette ordering in the antiferromagnetic SU(4) Heisenberg model. We find the ground state for both the square and triangular lattices to be the disconnected plaquette state. Our mean-field theory gives a first-order transition for plaquette ordering for the triangular lattice. Our results suggest a large number of low-lying states.
Tue, 01 Jan 2002 00:00:00 GMThttp://hdl.handle.net/10722/1748282002-01-01T00:00:00Z
- Chiral optical resonance of vortex core states in type-II superconductorshttp://hdl.handle.net/10722/174859Title: Chiral optical resonance of vortex core states in type-II superconductors
Authors: Zhu, YD; Zhang, FC; Drew, HD
Abstract: The dynamic conductivity of vortex cores in type-II superconductors is calculated. We show that there is a chiral optical resonance well below the superconducting gap, corresponding to creating a pair of quasiparticles inside the vortex core. The chirality is the same as cyclotron resonance. The frequency and intensity of the resonance are estimated by numerically solving the Bogoliubov de Gennes equations self-consistently. © 1993 The American Physical Society.
Fri, 01 Jan 1993 00:00:00 GMThttp://hdl.handle.net/10722/1748591993-01-01T00:00:00Z
- Coexistence of ferromagnetism and superconductivity in Cu-rich lanthanum Cu-oxideshttp://hdl.handle.net/10722/174864Title: Coexistence of ferromagnetism and superconductivity in Cu-rich lanthanum Cu-oxides
Authors: Zhao, BR; Dong, XL; Luo, PS; Gao, M; Zhao, ZX; Peng, LM; Ni, YM; Qiu, XG; Awaji, S; Watanabe, K; Wu, F; Xu, B; Zhao, LH; Zhang, FC
Abstract: We have measured the zero field and field cooled magnetization of the lightly oxygen doped Cu-rich La 2CuO 4+δ in a wide temperature range (5 K to 350 K). The data together with the evolution of the magnetic hyteresis loop suggest that the ferromagnetism with Curie temperature of 280 K coexists with superconductivity below the transition temperature ∼ 34 K. The coexistence occurs in the hole-rich clusters of size ≤ 150 nm, which are electronic phase separated from the hole-poor antiferromagnetic background.
Tue, 01 Jan 2002 00:00:00 GMThttp://hdl.handle.net/10722/1748642002-01-01T00:00:00Z
- Theory for spin and orbital orderings in high-temperature phases in YVO 3http://hdl.handle.net/10722/174889Title: Theory for spin and orbital orderings in high-temperature phases in YVO 3
Authors: De Silva, TN; Joshi, A; Ma, M; Zhang, FC
Abstract: Motivated by the recent neutron-diffraction experiment on YVO 3, we consider a microscopic model where each V 3+ ion is occupied by two 3d electrons of parallel spins with twofold-degenerate orbital configurations. The mean-field classical solutions of the spin-orbital superexchange model predicts an antiferro-orbital ordering at a higher temperature followed by a C-type antiferromagnetic spin ordering at a lower temperature. Our results are qualitatively consistent with the observed orbital phase transition at ∼200 K and the spin phase transition at ∼114 K in YVO 3.
Wed, 01 Jan 2003 00:00:00 GMThttp://hdl.handle.net/10722/1748892003-01-01T00:00:00Z
- Spectral density and magnetic susceptibility for the asymmetric degenerate Anderson modelhttp://hdl.handle.net/10722/174891Title: Spectral density and magnetic susceptibility for the asymmetric degenerate Anderson model
Authors: Zhang, FC; Lee, TK
Abstract: With the use of a new diagrammatic formulation, two coupled integral equations for the self-energy functions of the f hole and f particle in the asymmetric degenerate Anderson model are solved numerically. All the diagrams are included in the equations except the cross terms (or the vertex correction). The results for the spectral density function and the magnetic susceptibility show the scaling property described by the renormalization-group theory. © 1984 The American Physical Society.
Sun, 01 Jan 1984 00:00:00 GMThttp://hdl.handle.net/10722/1748911984-01-01T00:00:00Z