238 research outputs found
Charge stripes due to electron correlations in the two-dimensional spinless Falicov-Kimball model
We calculate the restricted phase diagram for the Falicov-Kimball model on a
two-dimensional square lattice. We consider the limit where the conduction
electron density is equal to the localized electron density, which is the limit
related to the S_z=0 states of the Hubbard model. After considering over 20,000
different candidate phases (with a unit cell of 16 sites or less) and their
thermodynamic mixtures, we find only about 100 stable phases in the
ground-state phase diagram. We analyze these phases to describe where stripe
phases occur and relate these discoveries to the physics behind stripe
formation in the Hubbard model.Comment: (34 pages, 9 figures, submitted to Journal of Statistical Physics to
celebrate Elliott Lieb's 70th birthday
Strong-coupling expansion for ultracold bosons in an optical lattice at finite temperatures in the presence of superfluidity
We develop a strong-coupling () expansion technique for calculating
the density profile for bosonic atoms trapped in an optical lattice with an
overall harmonic trap at finite temperature and finite on site interaction in
the presence of superfluid regions. Our results match well with quantum Monte
Carlo simulations at finite temperature. We also show that the superfluid order
parameter never vanishes in the trap due to proximity effect. Our calculations
for the scaled density in the vacuum to superfluid transition agree well with
the experimental data for appropriate temperatures. We present calculations for
the entropy per particle as a function of temperature which can be used to
calibrate the temperature in experiments. We also discuss issues connected with
the demonstration of universal quantum critical scaling in the experiments.Comment: 11 pages, 9 figure
Quasi-universal transient behavior of a nonequilibrium Mott insulator driven by an electric field
We use a self-consistent strong-coupling expansion for the self-energy
(perturbation theory in the hopping) to describe the nonequilibrium dynamics of
strongly correlated lattice fermions. We study the three-dimensional
homogeneous Fermi-Hubbard model driven by an external electric field showing
that the damping of the ensuing Bloch oscillations depends on the direction of
the field, and that for a broad range of field strengths, a long-lived
transient prethermalized state emerges. This long-lived transient regime
implies that thermal equilibrium may be out of reach of the time scales
accessible in present cold atom experiments, but shows that an interesting new
quasi-universal transient state exists in nonequilibrium governed by a
thermalized kinetic energy but not a thermalized potential energy. In addition,
when the field strength is equal in magnitude to the interaction between atoms,
the system undergoes a rapid thermalization, characterized by a different
quasi-universal behavior of the current and spectral function for different
values of the hopping.Comment: (5 pages, 5 figures, ReVTeX
Electronic Raman scattering in correlated materials: exact treatment of nonresonant, mixed, and resonant scattering with dynamical mean field theory
We solve for the electronic Raman scattering response functions on an
infinite-dimensional hypercubic lattice employing dynamical mean field theory.
This contribution extends previous work on the nonresonant response to include
the mixed and resonant contributions. We focus our attention on the spinless
Falicov-Kimball model, where the problem can be solved exactly, and the system
can be tuned to go through a Mott-Hubbard-like metal-insulator transition.
Resonant effects vary in different scattering geometries, corresponding to the
symmetries of the charge excitations scattered by the light. We do find that
the Raman response is large near the double resonance, where the transfered
frequency is close to the incident photon frequency. We also find a joint
resonance of both the charge-transfer peak and the low-energy peak when the
incident photon frequency is on the order of the interaction strength. In
general, the resonance effects can create order of magnitude (or more)
enhancements of features in the nonresonant response, especially when the
incident photon frequency is somewhat larger than the frequency of the
nonresonant feature. Finally, we find that the resonant effects also exhibit
isosbestic behavior, even in the A1g and B2g sectors, and it is most prominent
when the incident photon frequency is on the order of the interaction energy.Comment: (20 pages, 13 figures
Thermoelectricity of EuCu{2}(Ge{1-x}Si{x}){2} intermetallics
The evolution of the thermopower EuCu{2}(Ge{1-x}Si{x}){2} intermetallics,
which is induced by the Si-Ge substitution, is explained by the Kondo
scattering of conduction electrons on the Eu ions which fluctuate between the
magnetic 2+ and non-magnetic 3+ Hund's rule configurations. The Si-Ge
substitution is equivalent to chemical pressure which modifies the coupling and
the relative occupation of the {\it f} and conduction states.Comment: 2 pages, Proceedings of the SCES 2005 confernece. Physica B (2006),
in pres
Simulation of inhomogeneous distributions of ultracold atoms in an optical lattice via a massively parallel implementation of nonequilibrium strong-coupling perturbation theory
We present a nonequilibrium strong-coupling approach to inhomogeneous systems
of ultracold atoms in optical lattices. We demonstrate its application to the
Mott-insulating phase of a two-dimensional Fermi-Hubbard model in the presence
of a trap potential. Since the theory is formulated self-consistently, the
numerical implementation relies on a massively parallel evaluation of the
self-energy and the Green's function at each lattice site, employing thousands
of CPUs. While the computation of the self-energy is straightforward to
parallelize, the evaluation of the Green's function requires the inversion of a
large sparse matrix, with . As a crucial ingredient,
our solution heavily relies on the smallness of the hopping as compared to the
interaction strength and yields a widely scalable realization of a rapidly
converging iterative algorithm which evaluates all elements of the Green's
function. Results are validated by comparing with the homogeneous case via the
local-density approximation. These calculations also show that the
local-density approximation is valid in non-equilibrium setups without mass
transport.Comment: 14 pages, 9 figure
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