226 research outputs found
Scaling limit of the one-dimensional attractive Hubbard model: The non-half-filled band case
The scaling limit of the less than half filled attractive Hubbard chain is
studied. This is a continuum limit in which the particle number per lattice
site, n, is kept finite (0<n<1) while adjusting the interaction and bandwidth
in a such way that there is a finite mass gap. We construct this limit both for
the spectrum and the secular equations describing the excitations. We find,
that similarly to the half filled case, the limiting model has a massive and a
massless sector. The structure of the massive sector is closely analogous to
that of the half filled band and consequently to the chiral invariant SU(2)
Gross-Neveu (CGN) model. The structure of the massless sector differs from that
of the half filled band case: the excitations are of particle and hole type,
however they are not uniquely defined. The energy and the momentum of this
sector exhibits a tower structure corresponding to a conformal field theory
with c=1 and SU(2)xSU(2) symmetry. The energy-momentum spectrum and the zero
temperature free energy of the states with finite density coincides with that
of the half filled case supporting the identification of the limiting model
with the SU(2) symmetric CGN theory.Comment: Latex, 28 page
Boundary S matrices for the open Hubbard chain with boundary fields
Using the method introduced by Grisaru et al., boundary S matrices for the
physical excitations of the open Hubbard chain with boundary fields are
studied. In contrast to the open supersymmetric t-J model, the boundary S
matrix for the charge excitations depend on the boundary fields though the
boundary fields do not break the spin-SU(2) symmetry.Comment: Latex,12 page
Scaling limit of the one-dimensional attractive Hubbard model: The half-filled band case
The scaling limit of the higher level Bethe Ansatz (HLBA) equations for a
macroscopically half-filled Hubbard chain is considered. These equations
practically decouple into three disjoint sets which are again of the BA type,
and correspond to the secular equations of three different kinds of dressed
particles (one massive and two massless). The finite size corrections and the
fine structure of the spectrum show that the massless sector corresponds to a
conformal field with central charge c=1 and Gaussian anomalous dimensions. The
zero temperature free energy is also calculated and is found to be in perfect
agreement with the results of a perturbative calculation in the SU(2) chiral
Gross-Neveu (CGN) model.Comment: LATEX, uses Revtex, 39 page
Exact Drude weight for the one-dimensional Hubbard model at finite temperatures
The Drude weight for the one-dimensional Hubbard model is investigated at
finite temperatures by using the Bethe ansatz solution. Evaluating finite-size
corrections to the thermodynamic Bethe ansatz equations, we obtain the formula
for the Drude weight as the response of the system to an external gauge
potential. We perform low-temperature expansions of the Drude weight in the
case of half-filling as well as away from half-filling, which clearly
distinguish the Mott-insulating state from the metallic state.Comment: 9 pages, RevTex, To appear in J. Phys.
Trapped interacting two-component bosons
In this paper we solve one dimensional trapped SU(2) bosons with repulsive
-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.Comment: 15 pages, 9 figure
Thermodynamics of Kondo Model with Electronic Interactions
On the basis of Bethe ansatz solution of one dimensional Kondo model with
electronic interaction, the thermodynamics equilibrium of the system in finite
temperature is studied in terms of the strategy of Yang and Yang. The string
hypothesis in the spin rapidity is discussed extensively. The thermodynamics
quantities, such as specific heat and magnetic susceptibility, are obtained.Comment: 8 pages, 0 figures, Revte
Hubbard physics in the symmetric half-filled periodic Anderson-Hubbard model
Two very different methods -- exact diagonalization on finite chains and a
variational method -- are used to study the possibility of a metal-insulator
transition in the symmetric half-filled periodic Anderson-Hubbard model. With
this aim we calculate the density of doubly occupied sites as a function of
various parameters. In the absence of on-site Coulomb interaction ()
between electrons, the two methods yield similar results. The double
occupancy of levels remains always finite just as in the one-dimensional
Hubbard model. Exact diagonalization on finite chains gives the same result for
finite , while the Gutzwiller method leads to a Brinkman-Rice transition
at a critical value (), which depends on and .Comment: 10 pages, 5 figure
A gapless charge mode induced by the boundary states in the half-filled Hubbard open-chain
We discuss the ground state and some excited states of the half-filled
Hubbard model defined on an open chain with L sites, where only one of the
boundary sites has a different value of chemical potential. We consider the
case when the boundary site has a negative chemical potential -p and the
Hubbard coupling U is positive. By an analytic method we show that when p is
larger than the transfer integral some of the ground-state solutions of the
Bethe ansatz equations become complex-valued. It follows that there is a
``surface phase transition'' at some critical value p_c; when p<p_c all the
charge excitations have the gap for the half-filled band, while there exists a
massless charge mode when p>p_c.Comment: Revtex, 25 pages, 3 eps figures; Full revision with Appendixes adde
- …