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Zu-Jian Ying

Publications and source records attributed to Zu-Jian Ying.

53 records · Page 3Linked to original sources
arXiv2016

Designing Electron Spin Textures and Spin Interferometers by Shape Deformations

We demonstrate that the spin orientation of an electron propagating in a one-dimensional nanostructure with Rashba spin-orbit (SO) coupling can be manipulated on demand by changing the geometry of the nanosystem. Shape deformations that result in a non-uniform curvature give rise to complex three-dimensional spin textures in space. We employ the paradigmatic example of an elliptically deformed quantum ring to unveil the way to get an all-geometrical and all-electrical control of the spin orientation. The resulting spin textures exhibit a tunable topological character with windings around the radial and the out-of-plane directions. We show that these topologically non trivial spin patterns affect the spin interference effect in the deformed ring, thereby resulting in different geometry-driven ballistic electronic transport behaviors. Our results establish a deep connection between electronic spin textures, spin transport and the nanoscale shape of the system.

cond-mat.mes-hall↗
arXiv2015

Ground-state phase diagram of the quantum Rabi model

The Rabi model plays a fundamental role in understanding light-matter interaction. It reduces to the Jaynes-Cummings model via the rotating-wave approximation, which is applicable only to the cases of near resonance and weak coupling. However, recent experimental breakthroughs in upgrading light-matter coupling order require understanding the physics of the full quantum Rabi model (QRM). Despite the fact that its integrability and energy spectra have been exactly obtained, the challenge to formulate an exact wavefunction in a general case still hinders physical exploration of the QRM. Here we unveil a ground-state phase diagram of the QRM, consisting of a quadpolaron and a bipolaron as well as their changeover in the weak-, strong- and intermediate-coupling regimes, respectively. An unexpected overweighted antipolaron is revealed in the quadpolaron state, and a hidden scaling behavior relevant to symmetry breaking is found in the bipolaron state. An experimentally accessible parameter is proposed to test these states, which might provide novel insights into the nature of the light-matter interaction for all regimes of the coupling strengths.

quant-ph↗
arXiv2015

No-go theorem for the description of Mott phenomena with conventional Density Functional Theory methods

Density functional theory provides the most widespread framework for the realistic description of the electronic structure of solids, but the description of strongly-correlated systems has remained so far elusive. Here we consider a particular limit of electrons in a periodic ionic potential in which a one-band description becomes exact all the way from the weakly-correlated metallic regime to the strongly-correlated Mott-Hubbard regime. We provide a necessary condition a density functional should fulfill to describe Mott-Hubbard behavior and show that it is not satisfied by standard and widely used local, semilocal and hybrid functionals. We illustrate the condition in the case of a few-atom system and provide an analytic approximation to the exact exchange-correlation potential based on a variational wave function which shows explicitly the correct behavior providing a robust scheme to combine lattice and continuum methods.

cond-mat.str-el↗
arXiv2014

Solving lattice density functionals close to the Mott regime

We study a lattice version of the local density approximation (LDA) based on Behte ansatz (BALDA). Contrary to what happens in Density Functional Theory (DFT) in the continuum and despite its name, BALDA displays some very non-local features and it has a discontinuous functional derivative. The same features prevent the convergence of the self-consistent Kohn-Sham cycle thus hindering the study of BALDA solutions close to a Mott phase or in the Coulomb blockade regime. Here we propose a numerical approach which, differently from previous works, does not introduce ad hoc parameters to smear out the singularity. Our results are relevant for all lattice models where BALDA is applied ranging from Kondo systems to harmonically trapped Hubbard fermions. As an example we apply the method to the study of a one-dimensional lattice model with Hubbard interaction and a staggered potential which can be driven from an ionic to a Mott insulating state. In the Mott regime the presence of a "vacuum" allows us to calculate the different contribution to the gap and to highlight an ultranonlocality of BALDA.

cond-mat.str-el↗
arXiv2004

Quantum phase transitions and magnetization of an integrable spin ladder with new parameters in bridging to real compounds

We study the field-induced quantum phase transitions (QPT) and the relevant magnetic properties of a spin-1/2 two-leg integrable spin ladder (ISL), of which the system parameters in bridging to the real compounds are determined by setting the extra interactions in the Hamiltonian of the ISL relative to the Heisenberg spin ladder to vanish in the expectation in the ground state (GS). Such an ISL analytically has the correct leading terms of both the critical fields of the two QPT's as in the real strongly-coupled compounds: gμ_BH_{c1}=J_{\perp}-J_{\parallel} and gμ_BH_{c2}=J_{\perp}+2J_{\parallel} in terms of the experimental leg (J_{\parallel}) and rung (J_{\perp}) interactions. The symmetric magnetization inflection point is located at gμ_BH_{IP}=J_{\perp}+J_{\parallel}/2. The magnetizations for the GS and at finite temperatures, as well as the susceptibility, show good agreements in various comparisons with the finite-site exact diagonalization, the transfer-matrix renormalization group numerical result, the perturbation theory, and the compounds (5IAP)_2CuBr_4\cdot 2H_2O, Cu_2(C_5H_{12}N_2)_2Cl_4 and (C_5H_{12}N)_2CuBr_4.

cond-mat.str-el↗
arXiv2004

Exact solution and magnetic properties of an anisotropic spin ladder

We study an integrable two-leg spin-1/2 ladder with an XYZ-type rung interaction. Exact rung states and rung energies are obtained for the anisotropic rung coupling in the presence of a magnetic field. Magnetic properties are analyzed at both zero and finite temperatures via the thermodynamic Bethe ansatz and the high-temperature expansion. According to different couplings in the anisotropic rung interaction, there are two cases in which a gap opens, with the ground state involving one or two components in the absence of a magnetic field. We obtain the analytic expressions of all critical fields for the field-induced quantum phase transitions (QPT). Anisotropic rung interaction leads to such effects as separated magnetizations and susceptibilities in different directions, lowered inflection points and remnant weak variation of the magnetization after the last QPT.

cond-mat.stat-mech↗
arXiv2003

Effect of one-ion L-S coupling on magnetic properties of a correlated spin-orbit system

By introducing a basis for a novel realization of the SU(4) Lie algebra, we exactly solve a spin-orbital chain with one-ion $L$-$S$ coupling (OILSC) via the Bethe ansatz (BA) approach. In the context of different Landé $g$ factors of the spin and orbital sectors, the OILSC results in rich and novel quantum phase transitions. Some accurate analytical expressions for the critical fields are obtained. Both spin ordering and orbital ordering are found in a gapped singlet phase. The system exhibits many interesting phenomena such as nonvanishing magnetization of the singlet phase, multi-entrance of the singlet in the ground state when the field varies, unsymmetric magnetization in two-component phase and magnetization crossover for different OILSC.

cond-mat.str-el↗
arXiv2003

Magnetization plateau and quantum phase transitions in a spin-orbital model

A spin-orbital chain with different Landé $g$ factors and one-ion anisotropy is studied in the context of the thermodynamical Bethe ansatz. It is found that there exists a magnetization plateau resulting from the different Landé $g$ factors. Detailed phase diagram in the presence of an external magnetic field is presented both numerically and analytically. For some values of the anisotropy, the four-component system undergoes five consecutive quantum phase transitions when the magnetic field varies. We also study the magnetization in various cases, especially its behaviors in the vicinity of the critical points. For the SU(4) spin-orbital model, explicit analytical expressions for the critical fields are derived, with excellent accuracy compared with numerics.

cond-mat.str-el↗
arXiv2003

One dimensional SU(3) bosons with $δ$ function interaction

In this paper we solve one dimensional SU(3) bosons with repulsive $δ$-function interaction by means of Bethe ansatz method. The features of ground state and low-lying excited states are studied by both numerical and analytic methods. We show that the ground state is a SU(3) color ferromagnetic state. The configurations of quantum numbers for the ground state are given explicitly. For finite $N$ system the spectra of low-lying excitations and the dispersion relations of four possible elementary particles (holon, antiholon, $σ$-coloron and $ω$-coloron) are obtained by solving Bethe-ansatz equation numerically. The thermodynamic equilibrium of the system at finite temperature is studied by using the strategy of thermodynamic Bethe ansatz, a revised Gaudin-Takahashi equation which is useful for numerical method are given . The thermodynamic quantities, such as specific heat, are obtain for some special cases. We find that the magnetic property of the model in high temperature regime is dominated by Curie's law: $χ\propto 1/T$ and the system has Fermi-liquid like specific heat in the strong coupling limit at low temperature.

cond-mat.str-el↗
arXiv2002

Thermodynamics of SU(2) bosons in one dimension

On the basis of Bethe ansatz solution of two-component bosons with SU(2) symmetry and $δ$-function interaction in one dimension, we study the thermodynamics of the system at finite temperature by using the strategy of thermodynamic Bethe ansatz (TBA). It is shown that the ground state is an isospin "ferromagnetic" state by the method of TBA, and at high temperature the magnetic property is dominated by Curie's law. We obtain the exact result of specific heat and entropy in strong coupling limit which scales like $T$ at low temperature. While in weak coupling limit, it is found there is still no Bose-Einstein Condensation (BEC) in such 1D system.

cond-mat.str-el↗
arXiv2001

Low temperature properties of one-dimensional SU(4) Hubbard-like model at low concentration

On the basis of Bethe ansatz solution of one dimensional SU(4) Hubbard-like model, we study its thermodynamics properties by means of Yang-Yang thermodynamics Bethe ansatz. The Landé $g$ factor is taken into account so as to describe electrons with orbital degeneracy. The free energy at low temperature is given and the specific heat both in strong coupling and weak coupling limits are obtained.

cond-mat.str-el↗
arXiv2001

Trapped interacting two-component bosons

In this paper we solve one dimensional trapped SU(2) bosons with repulsive $δ$-function interaction by means of Bethe-ansatz method. The features of ground state and low-lying excited states are studied by numerical and analytic methods. We show that the ground state is an isospin "ferromagnetic" state which differs from spin-1/2 fermions system. There exist three quasi-particles in the excitation spectra, and both holon-antiholon and holon-isospinon excitations are gapless for large systems. The thermodynamics equilibrium of the system at finite temperature is studied by thermodynamic Bethe ansatz. The thermodynamic quantities, such as specific heat etc. are obtained for the case of strong coupling limit.

cond-mat.str-el↗
arXiv2001

Two component interacting bosons: 1-d exact results

Motivated by the experiment of two-component Bose-Einstein condensates produced in magnetically trapped $^{87}Rb$, we study one dimensional Boson systems with repulsive $δ$-function interaction in the presence of SU(2) intrinsic degree of freedom by means of coordinate Bethe ansatz. The ground state and low-lying excitations are solved by both numerical and analytical methods. It is shown that the ground state is an isospin-ferromagnetic state and the excitations are composed of three elementary particles: holons, antiholons and isospinons. The isospinon is a triplet coupled to the ``ferromagnetic'' background antiparallelly.

cond-mat.str-el↗
arXiv2001

Symmetries in the Hubbard model with n-fold orbital degeneracy

The present paper studies the symmeries of the Hubbard model of electrons with generally $n$-fold orbital degeneracy. It's shown SU_d(2n) and SU_c(2n) symmetries hold respectively for the model with completely repulsive or attractive on-site interaction and that with partly attractive interactions. An extended Lieb-Mattis transformation is given to map these two symmetries into each other. The sub-symmetry SU_d^{(e)}(n)\otimes SU_d^{(o)}(n) is found to be shared by the two models with arbitrary chemical potential μ. By assuming at most two electrons on each site it's found that $SU_d(2n)$ and $SU_c(2n)$ both exist in each kind of the two models and consequently lead to a larger symmetry SU_d(2n)\times SU_c(2n). Another underlying symmetry SU_c^{(e)}(2)_{\cal P}\times ...\times SU_c^{(e)}(2)_{\cal P} \otimes \bigl(SU_c^{(o)}(2)_{\cal P}\times ...\times SU_c^{(o)}(2)_{\cal P}\bigr) is also revealed for the unified $U$ model under the excluding. The symmetry is valid for the partially attractive model with chemical potential $μ=-U.$

cond-mat.str-el↗
arXiv2000

Thermodynamics of trapped interacting bosons in one dimension

On the basis of Bethe ansatz solution of bosons with delta-function interaction in a one-dimensional potential well, the thermodynamics equilibrium of the system in finite temperature is studied by using the strategy of Yang and Yang. The thermodynamics quantities, such as specific heat etc. are obtained for the cases of strong coupling limit and weak coupling limit respectively.

cond-mat↗
arXiv1999

Equation of motion approach to the solution of Anderson model

Based on an equation of motion approach the single impurity Anderson model(SIAM) is reexamined. Using the cluster expansions the equations of motion of Green functions are transformed into the corresponding equations of motion of connected Green functions, which provides a natural and uniform truncation scheme. A factor of two missing in the Lacroix's approximation for the Kondo temperature is gained in the next higher order truncation beyond Lacroix's. A quantitative improvement in the density of states at the Fermi level is also obtained.

cond-mat.str-el↗