375 research outputs found
Commuting quantum transfer matrix approach to intrinsic Fermion system: Correlation length of a spinless Fermion model
The quantum transfer matrix (QTM) approach to integrable lattice Fermion
systems is presented. As a simple case we treat the spinless Fermion model with
repulsive interaction in critical regime. We derive a set of non-linear
integral equations which characterize the free energy and the correlation
length of for arbitrary particle density at any finite
temperatures. The correlation length is determined by solving the integral
equations numerically. Especially in low temperature limit this result agrees
with the prediction from conformal field theory (CFT) with high accuracy.Comment: 17 page
Exact thermodynamics of an Extended Hubbard Model of single and paired carriers in competition
By exploiting the technique of Sutherland's species, introduced in
\cite{DOMO-RC}, we derive the exact spectrum and partition function of a 1D
extended Hubbard model. The model describes a competition between dynamics of
single carriers and short-radius pairs, as a function of on-site Coulomb
repulsion () and filling (). We provide the temperature dependence of
chemical potential, compressibility, local magnetic moment, and specific heat.
In particular the latter turns out to exhibit two peaks, both related to
`charge' degrees of freedom. Their origin and behavior are analyzed in terms of
kinetic and potential energy, both across the metal-insulator transition point
and in the strong coupling regime.Comment: 14 pages, 15 eps figure
Exact results for the thermal and magnetic properties of strong coupling ladder compounds
We investigate the thermal and magnetic properties of the integrable su(4)
ladder model by means of the quantum transfer matrix method. The magnetic
susceptibility, specific heat, magnetic entropy and high field magnetization
are evaluated from the free energy derived via the recently proposed method of
high temperature expansion for exactly solved models. We show that the
integrable model can be used to describe the physics of the strong coupling
ladder compounds. Excellent agreement is seen between the theoretical results
and the experimental data for the known ladder compounds
(5IAP)CuBr2HO, Cu(CHN)Cl etc.Comment: 10 pages, 5 figure
Lattice path integral approach to the one-dimensional Kondo model
An integrable Anderson-like impurity model in a correlated host is derived
from a gl(21)-symmetric transfer matrix by means of the
Quantum-Inverse-Scattering-Method (QISM). Using the Quantum Transfer Matrix
technique, free energy contributions of both the bulk and the impurity are
calculated exactly. As a special case, the limit of a localized moment in a
free bulk (Kondo limit) is performed in the Hamiltonian and in the free energy.
In this case, high- and low-temperature scales are calculated with high
accuracy.Comment: 26 pages, 9 figure
Non-equilibrated post freeze out distributions
We discuss freeze out on the hypersurface with time-like normal vector,
trying to answer how realistic is to assume thermal post freeze out
distributions for measured hadrons. Using simple kinetic models for gradual
freeze out we are able to generate thermal post FO distribution, but only in
highly simplified situation. In a more advanced model, taking into account
rescattering and re-thermalization, the post FO distribution gets more
complicated. The resulting particle distributions are in qualitative agreement
with the experimentally measured pion spectra. Our study also shows that the
obtained post FO distribution functions, although analytically very different
from the Juttner distribution, do look pretty much like thermal distributions
in some range of parameters.Comment: 14 pages, 2 figures, EPJ style, submitted to EPJ
Impact of Nucleon Mass Shift on the Freeze Out Process
The freeze out of a massive nucleon gas through a finite layer with time-like
normal is studied. The impact of in-medium nucleon mass shift on the freeze out
process is investigated. A considerable modification of the thermodynamical
variables temperature, flow-velocity, energy density and particle density has
been found. Due to the nucleon mass shift the freeze out particle distribution
functions are changed noticeably in comparison with evaluations, which use
vacuum nucleon mass.Comment: submitted to Physical Review
Thermomagnetic Power and Figure of Merit for Spin-1/2 Heisenberg Chain
Transport properties in the presence of magnetic fields are numerically
studied for the spin-1/2 Heisenberg XXZ chain. The breakdown of the
spin-reversal symmetry due to the magnetic field induces the magnetothermal
effect. In analogy with the thermoelectric effect in electron systems, the
thermomagnetic power (magnetic Seebeck coefficient) is provided, and is
numerically evaluated by the exact diagonalization for wide ranges of
temperatures and various magnetic fields. For the antiferromagnetic regime, we
find the magnetic Seebeck coefficient changes sign at certain temperatures,
which is interpreted as an effect of strong correlations. We also compute the
thermomagnetic figure of merit determining the efficiency of the thermomagnetic
devices for cooling or power generation.Comment: 8 page
Thermodynamics and Crossover Phenomena in the Correlation Lengths of the One-Dimensional t-J Model
We investigate the thermodynamics of the one-dimensional t-J model using
transfer matrix renormalization group (TMRG) algorithms and present results for
quantities like particle number, specific heat, spin susceptibility and
compressibility. Based on these results we confirm a phase diagram consisting
of a Tomonaga-Luttinger liquid (TLL) phase for small J/t and a phase separated
state for J/t large. Close to phase separation we find a spin-gap
(Luther-Emery) phase at low densities consistent with predictions by other
studies. At the supersymmetric point we compare our results with exact results
from the Bethe ansatz and find excellent agreement. In particular we focus on
the calculation of correlation lengths and static correlation functions and
study the crossover from the non-universal high T lattice into the quantum
critical regime. At the supersymmetric point we compare in detail with
predictions by conformal field theory (CFT) and TLL theory and show the
importance of logarithmic corrections.Comment: 14 pages, 20 figure
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