Non-local Thirring model at finite temperature

We extend a recently proposed non-local and non-covariant version of the Thirring model to the finite-temperature case. We obtain a completely bosonized expression for the partition function, describing the thermodynamics of the collective modes which are the underlying excitations of this system. From this result we derive closed formulae for the free-energy, specific-heat, two-point correlation functions and momentum distribution, as functionals of electron-electron coupling potentials. © 1998 Elsevier Science B.V.     

A measure of conductivity for lattice fermions at finite density

We study the linear response to an external electric field of a system of fermions in a lattice at zero temperature. This allows to measure numerically the Euclidean conductivity which turns out to be compatible with an analytical calculation for free fermions. The numerical method is generalizable to systems with dynamical interactions where no analytical approach is possible.     

有限温度下一维Gaudin-Yang模型的热力学性质

本文通过数值求解有限温度下一维均匀费米Gaudin-Yang模型的热力学Bethe-ansatz方程, 研究了此模型的基本性质,得到了在给定的温度或给定的相互作用下, 化学势、相互作用、粒子密度和熵的相互变化图像. 对结果分析发现, 在给定温度和相互作用下, 熵随着化学势的变化有一个量子临界区域.     

Solvable lattice gas models of random hetero-polymers at finite density: I. Statics

We introduce -dimensional lattice gas versions of three common models of random hetero-polymers, in which both the polymer density and the density of the polymer-solvent mixture are finite. These solvable models give valuable insight into the problems related to the (quenched) average over the randomness in statistical mechanical models of proteins, without having to deal with the hard geometrical constraints occurring in finite-dimensional models. Our exact solution, which is specific to the -dimensional case, is compared to the results obtained by a saddle-point analysis and by the grand ensemble approach, both of which can also be applied to models of finite dimension. We find, somewhat surprisingly, that the saddle-point analysis can lead to qualitatively incorrect results. Received 15 June 1999 and Received in final form 14 October 1999     

Holographic model at finite temperature with R-charge density

We consider a holographic model of QCD at finite temperature with nonzero chemical potentials conjugate to R-charge densities. A critical surface of the confinement–deconfinement phase transition is shown for five-dimensional charged black hole solution given by Behrndt, Cvetič and Sabra. On a special section of the parameter space, we find a critical curve being similar to the one expected in QCD. We calculate meson spectra and decay constants in the confinement phase of this section to see their temperature and chemical potential dependences. We could assure generalized Gell-Mann–Oakes–Renner relation and the reduction of pion velocity near the critical point.     

Commensurability in one-dimensional lattices at finite temperature

The theory of commensurability transitions in one-dimensional atomic chains has been applied to charge density waves, mercury chain compounds, superionic conductors, etc. Previous numerical and analytical results on a model with chains of atoms with nearest neighbor interactions and periodic external potentials have dealt mainly with equilibrium and dynamical properties atT = 0 K. These studies are extended to nonzero temperatures. It is found that the reversible work per particle to slide the chain vanishes in the thermodynamic limit for any nonzero temperature. The mathematical pathologies associated with the commensurability transition atT= 0 (i.e., the devil's stair) are absent at finite temperature; only thermodynamic evidence of low-order Commensurability transitions remains.Supported by the Department of Energy, Contract number EG-77-S-02-4432.     

Phase transition in finite density and temperature lattice QCD

We investigate the behavior of the chiral condensate in lattice QCD at finite temperature and finite chemical potential. The study was done using two flavors of light quarks and with a series of β and ma at the lattice size 24×12²×6. The calculation was done in the Taylor expansion formalism. We are able to calculate the first and second order derivatives of <ψψ> in both isoscalar and isovector channels. With the first derivatives being small, we find that the second derivatives are sizable close to the phase transition and that the magnitude of ψψ decreases under the influence of finite chemical potential in both channels.     

Solvable lattice gas models of random heteropolymers at finite density: II. Dynamics and transitions to compact states

The European Physical Journal E - In this paper we analyse both the dynamics and the high density physics of the infinite dimensional lattice gas model for random heteropolymers recently introduced...     

Double-exchange ferromagnetism in the partially-filled one-dimensional Kondo lattice model

We investigate the incompletely saturated ferromagnetic phase which occurs at strong-coupling in the partially-filled one-dimensional (1D) Kondo lattice model. The double-exchange interaction responsible for the ferromagnetic ordering is absent in dilute Kondo systems, and is a missing element in nearly all theoretical treatments of the model. We discuss how: 1) double-exchange arises in the system, even though the Kondo coupling is antiferromagnetic, and show that at strong-coupling it favors an alignment of the spins of unpaired localized moments; and 2) how this determines the ground-state phase diagram, and properties of the localized moments.     

Persistent current and Drude weight for the one-dimensional Hubbard model from current lattice density functional theory

The Bethe ansatz local density approximation (LDA) to lattice density functional theory (LDFT) for the one-dimensional repulsive Hubbard model is extended to current-LDFT (CLDFT). The transport properties of mesoscopic Hubbard rings threaded by a magnetic flux are then systematically investigated by this scheme. In particular we present calculations of ground state energies, persistent currents and Drude weights for both a repulsive homogeneous and a single impurity Hubbard model. Our results for the ground state energies in the metallic phase compare favorably well with those obtained with numerically accurate many-body techniques. Also the dependence of the persistent currents on the Coulomb and the impurity interaction strength, and on the ring size are all well captured by LDA-CLDFT. Our study demonstrates the value of CLDFT in describing the transport properties of one-dimensional correlated electron systems. As its computational overheads are rather modest, we propose this method as a tool for studying problems where both disorder and interaction are present.     

有限温度下一维Hubbard模型的化学势泛函理论研究

通过数值方法求解了有限温度下一维均匀Hubbard模型的热力学Bethe-ansatz方程组,得到了在给定温度和相互作用强度情况下,比热c、磁化率χ和压缩比κ随化学势μ的变化图像.基于有限温度下一维均匀Hubbard模型的精确解,利用化学势(μ)-泛函理论研究了一维谐振势下的非均匀Hubbard模型,给出了金属态和Mott绝缘态下不同温度情况时局域粒子密度n_i和局域压缩比_κi随格点的变化情况.     

Eight-vertex model in lattice statistics and one-dimensional anisotropic heisenberg chain. II. Equivalence to a generalized ice-type lattice model

We establish an equivalence between the zero-field eight-vertex model and an Ising model (with four-spin interaction) in which each spin has L possible values, labeled 1, …, L, and two adjacent spins must differ by one (to modulus L). Such an Ising model can also be thought of as a generalized ice-type model and we will later show that the eigenvectors of the transfer matrix can be obtained by a Bethe-type ansatz.     

On the thermodynamics of an ideal fermi gas on the lattice at finite density

We study the ideal gas of fermions on a lattice at finite density for both naive and Wilson fermions. Comparing the thermodynamical quantities thus calculated with the known results in the continuum theory, we are led to propose a modification of the naive form of the lattice action, which is same for both the naive and the Wilson fermions. The thermodynamical quantities, calculated by using this form, are shown to have the correct continuum limit.