arXiv subjects

You-Quan Li

Publications and source records attributed to You-Quan Li.

At least 73 records · Page 4Linked to original sources

arXiv2004

Medium effects on the selection of sequences folding into stable proteins in a simple model

We study the medium effects on the selection of sequences in protein folding by taking account of the surface potential in HP-model. Our analysis on the proportion of H and P monomers in the sequences gives a direct interpretation that the lowly designable structures possess small average gap. The numerical calculation by means of our model exhibits that the surface potential enhances the average gap of highly designable structures. It also shows that a most stable structure may be no longer the most stable one if the medium parameters changed.

q-bio.BM↗

arXiv2004

Charge Ordered RVB States in the Doped Cuprates

We study charge ordered d-wave resonating valence bond states (dRVB) in the doped cuprates, and estimate the energies of these states in a generalized $t-J $ model by using a renormalized mean field theory. The long range Coulomb potential tends to modulate the charge density in favor of the charge ordered RVB state. The possible relevance to the recently observed $4 \times 4$ checkerboard patterns in tunnelling conductance in high $T_c$ cuprates is discussed.

cond-mat.str-el↗

arXiv2004

On the ground state and excitations of a four-component fermion model

The properties of the ground state and excitations of a four-component Hubbard-like model are studied by the Lieb-Schultz-Mattis approach. It is proven rigorously that the ground state of the model is nondegenerate and excitations are gapless at all band fillings.

cond-mat.str-el↗

arXiv2004

The entanglement of Heisenberg chain with next-nearest-neighbor interaction

The features of the concurrences of the nearest-neighbor and the next-nearest-neighbor sites for one-dimensional Heisenberg model with the next-nearest-neighbor interaction are studied both at the ground state and finite temperatures respectively. Both concurrences are found to exhibit different behaviors at the ground state, which is clarified from the point of view of the correlation function. The threshold temperature with respective to different number of sites and the thermal concurrences of the system up to 12 sites are studied numerically.

quant-ph↗

arXiv2003

Entanglement, quantum phase transition and scaling in XXZ chain

Motivated by recent development in quantum entanglement, we study relations among concurrence $C$, SU$_q$(2) algebra, quantum phase transition and correlation length at the zero temperature for the XXZ chain. We find that at the SU(2) point, the ground state possess the maximum concurrence. When the anisotropic parameter $Δ$ is deformed, however, its value decreases. Its dependence on $Δ$ scales as $C=C_0-C_1(Δ-1)^2$ in the XY metallic phase and near the critical point (i.e. $1<Δ<1.3$) of the Ising-like insulating phase. We also study the dependence of $C$ on the correlation length $ξ$, and show that it satisfies $C=C_0-1/2ξ$ near the critical point. For different size of the system, we show that there exists a universal scaling function of $C$ with respect to the correlation length $ξ$.

quant-ph↗

arXiv2003

Local entanglement and quantum phase transition in the Hubbard model

The local entanglement $E_v$ of the one-dimensional Hubbard model is studied on the basis of its Bethe-ansatz solution. The relationship between the local entanglement and the on-site Coulomb interaction $U$ is obtained. Our results show that $E_v$ is an even analytic function of $U$ at half-filling and it reaches a maximum at the critical point U=0. The variation of the local entanglement with the filling factor shows that the ground state with maximal symmetry possesses maximal entanglement. The magnetic field makes the local entanglement to decrease and approach to zero at saturated magnetization. The on-site Coulomb interaction always suppresses the local entanglement.

quant-ph↗

arXiv2003

Phase diagram and symmetry breaking of SU(4) spin-orbital chain in a generalized external field

The ground state phases of a one-dimensional SU(4) spin-orbital Hamiltonian in a generalized external field are studied on the basis of Bethe-ansatz solution. Introducing three Landé $g$ factors for spin, orbital and their products in the SU(4) Zeeman term, we discuss systematically the various symmetry breaking. The magnetization versus external field are obtained by solving Bethe-ansatz equations numerically. The phase diagrams corresponding to distinct residual symmetries are given by means of both numerical and analytical methods.

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

Numerical and Monte Carlo Bethe ansatz method: 1D Heisenberg model

In this paper we present two new numerical methods for studying thermodynamic quantities of integrable models. As an example of the effectiveness of these two approaches, results from numerical solutions of all sets of Bethe ansatz equations, for small Heisenberg chains, and Monte Carlo simulations in quasi-momentum space, for a relatively larger chains, are presented. Our results agree with those obtained by thermodynamics Bethe ansatz (TBA) and Quantum Transfer Matrix (QTM).

cond-mat.str-el↗

arXiv2002

Magnetic properties of an SU(4) spin-orbital chain

In this paper, we study the magnetic properties of the one-dimensional SU(4) spin-orbital model by solving its Bethe ansatz solution numerically. It is found that the magnetic properties of the system for the case of $g_t=1.0$ differs from that for the case of $g_t=0.0$. The magnetization curve and susceptibility are obtained for a system of 200 sites. For $0<g_t<g_s$, the phase diagram depending on the magnetic field and the ratio of Landé factors, $g_t/g_s$, is obtained. Four phases with distinct magnetic properties are found.

cond-mat.str-el↗

arXiv2002

Rigorous Proof of Pseudospin Ferromagnetism in Two-Component Bosonic Systems with Component-Independent Interactions

For a two-component bosonic system, the components can be mapped onto a pseudo-spin degree of freedom with spin quantum number S=1/2. We provide a rigorous proof that for a wide-range of real Hamiltonians with component independent mass and interaction, the ground state is a ferromagnetic state with pseudospin fully polarized. The spin-wave excitations are studied and found to have quadratic dispersion relations at long wave length.

cond-mat.soft↗

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↗

arXiv2002

Rigorous results for a hierarchy of generalized Heisenberg models

The Lieb-Schultz-Mattis theorem is extended to generalized Heisenberg models related to non-exceptional Lie algebras. It is shown that there are no energy gaps above the ground sates for SO(4), Sp(2) and SU(4) Heisenberg models, gaps are suspected to occur in SO(5) and SO(6) models. The nondegenerate ground state for these models is rigorously proven.

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↗