311 research outputs found
Thermodynamics of strongly interacting fermions in two-dimensional optical lattices
We study finite-temperature properties of strongly correlated fermions in
two-dimensional optical lattices by means of numerical linked cluster
expansions, a computational technique that allows one to obtain exact results
in the thermodynamic limit. We focus our analysis on the strongly interacting
regime, where the on-site repulsion is of the order of or greater than the band
width. We compute the equation of state, double occupancy, entropy, uniform
susceptibility, and spin correlations for temperatures that are similar to or
below the ones achieved in current optical lattice experiments. We provide a
quantitative analysis of adiabatic cooling of trapped fermions in two
dimensions, by means of both flattening the trapping potential and increasing
the interaction strength.Comment: 7 pages, 7 figure
Thermodynamics of the Antiferromagnetic Heisenberg Model on the Checkerboard Lattice
Employing numerical linked-cluster expansions (NLCEs) along with exact
diagonalizations of finite clusters with periodic boundary condition, we study
the energy, specific heat, entropy, and various susceptibilities of the
antiferromagnetic Heisenberg model on the checkerboard lattice. NLCEs, combined
with extrapolation techniques, allow us to access temperatures much lower than
those accessible to exact diagonalization and other series expansions. We find
that the high-temperature peak in specific heat decreases as the frustration
increases, consistent with the large amount of unquenched entropy in the region
around maximum classical frustration, where the nearest-neighbor and
next-nearest neighbor exchange interactions (J and J', respectively) have the
same strength, and with the formation of a second peak at lower temperatures.
The staggered susceptibility shows a change of character when J' increases
beyond 0.75J, implying the disappearance of the long-range antiferromagnetic
order at zero temperature. For J'=4J, in the limit of weakly coupled crossed
chains, we find large susceptibilities for stripe and Neel order with
Q=(pi/2,pi/2) at low temperatures with antiferromagnetic correlations along the
chains. Other magnetic and bond orderings, such as a plaquette valence-bond
solid and a crossed-dimer order suggested by previous studies, have also been
investigated.Comment: 10 pages, 13 figure
Thermodynamic Properties of Kagome Antiferromagnets with different Perturbations
We discuss the results of several small perturbations to the thermodynamic
properties of Kagome Lattice Heisenberg Model (KLHM) at high and intermediate
temperatures, including Curie impurities, dilution, in-plane and out of plane
Dzyaloshinski-Moria (DM) anisotropies and exchange anisotropy. We examine the
combined role of Curie impurities and dilution in the behavior of uniform
susceptibility. We also study the changes in specific heat and entropy with
various anisotropies. Their relevance to newly discovered materials
ZnCu3(OH)6Cl2 is explored. We find that the magnetic susceptibility is well
described by about 6 percent impurity and dilution. We also find that the
entropy difference between the material and KLHM is well described by the DM
parameter D_z/J~0.1.Comment: 6 pages, 3 figures, proceedings of the HFM 2008 Conferenc
Phase coherence, visibility, and the superfluid--Mott-insulator transition on one-dimensional optical lattices
We study the phase coherence and visibility of trapped atomic condensates on
one-dimensional optical lattices, by means of quantum Monte-Carlo simulations.
We obtain structures in the visibility similar to the kinks recently observed
experimentally by Gerbier et.al.[Phy. Rev. Lett. 95, 050404 (2005); Phys. Rev.
A 72, 053606 (2005)]. We examine these features in detail and offer a
connection to the evolution of the density profiles as the depth of the lattice
is increased. Our simulations reveal that as the interaction strength, U, is
increased, the evolution of superfluid and Mott-insulating domains stall for
finite intervals of U. The density profiles do not change with increasing U. We
show here that in one dimension the visibility provides unequivocal signatures
of the melting of Mott domains with densities larger than one.Comment: 4 pages, 5 figure
Numerical Linked-Cluster Algorithms. II. t-J models on the square lattice
We discuss the application of a recently introduced numerical linked-cluster
(NLC) algorithm to strongly correlated itinerant models. In particular, we
present a study of thermodynamic observables: chemical potential, entropy,
specific heat, and uniform susceptibility for the t-J model on the square
lattice, with J/t=0.5 and 0.3. Our NLC results are compared with those obtained
from high-temperature expansions (HTE) and the finite-temperature Lanczos
method (FTLM). We show that there is a sizeable window in temperature where NLC
results converge without extrapolations whereas HTE diverges. Upon
extrapolations, the overall agreement between NLC, HTE, and FTLM is excellent
in some cases down to 0.25t. At intermediate temperatures NLC results are
better controlled than other methods, making it easier to judge the convergence
and numerical accuracy of the method.Comment: 7 pages, 12 figures, as publishe
Superfluid and Mott Insulator phases of one-dimensional Bose-Fermi mixtures
We study the ground state phases of Bose-Fermi mixtures in one-dimensional
optical lattices with quantum Monte Carlo simulations using the Canonical Worm
algorithm. Depending on the filling of bosons and fermions, and the on-site
intra- and inter-species interaction, different kinds of incompressible and
superfluid phases appear. On the compressible side, correlations between bosons
and fermions can lead to a distinctive behavior of the bosonic superfluid
density and the fermionic stiffness, as well as of the equal-time Green
functions, which allow one to identify regions where the two species exhibit
anticorrelated flow. We present here complete phase diagrams for these systems
at different fillings and as a function of the interaction parameters.Comment: 8 pages, 12 figure
Free expansion of impenetrable bosons on one-dimensional optical lattices
We review recent exact results for the free expansion of impenetrable bosons
on one-dimensional lattices, after switching off a confining potential. When
the system is initially in a superfluid state, far from the regime in which the
Mott-insulator appears in the middle of the trap, the momentum distribution of
the expanding bosons rapidly approaches the momentum distribution of
noninteracting fermions. Remarkably, no loss in coherence is observed in the
system as reflected by a large occupation of the lowest eigenstate of the
one-particle density matrix. In the opposite limit, when the initial system is
a pure Mott insulator with one particle per lattice site, the expansion leads
to the emergence of quasicondensates at finite momentum. In this case,
one-particle correlations like the ones shown to be universal in the
equilibrium case develop in the system. We show that the out-of-equilibrium
behavior of the Shannon information entropy in momentum space, and its contrast
with the one of noninteracting fermions, allows to differentiate the two
different regimes of interest. It also helps in understanding the crossover
between them.Comment: 21 pages, 14 figures, invited brief revie
Focus on out-of-equilibrium dynamics in strongly interacting one-dimensional systems
In the past few years, there have been significant advances in understanding out-of-equilibrium dynamics in strongly interacting many-particle quantum systems. This is the case for 1D dynamics, where experimental advances - both with ultracold atomic gases and with solid state systems - have been accompanied by advances in theoretical methods, both analytical and numerical. This 'focus on' collection brings together 17 new papers, which together give a representative overview of the recent advances
Coherent matter waves emerging from Mott-insulators
We study the formation of (quasi-)coherent matter waves emerging from a Mott
insulator for strongly interacting bosons on a one-dimensional lattice. It has
been shown previously that a quasi-condensate emerges at momentum k=\pi/2a,
where a is the lattice constant, in the limit of infinitely strong repulsion
(hard-core bosons). Here we show that this phenomenon persists for all values
of the repulsive interaction that lead to a Mott insulator at a commensurate
filling. The non-equilibrium dynamics of hard-core bosons is treated exactly by
means of a Jordan-Wigner transformation, and the generic case is studied using
a time-dependent density matrix renormalization group technique. Different
methods for controlling the emerging matter wave are discussed.Comment: 20 pages, 11 figures. Published versio
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