274 research outputs found
Density of States and Magnetic Correlations at a Metal-Mott Insulator Interface
The possibility of novel behavior at interfaces between strongly and weakly
correlated materials has come under increased study recently. In this paper, we
use determinant Quantum Monte Carlo to determine the inter-penetration of
metallic and Mott insulator physics across an interface in the two dimensional
Hubbard Hamiltonian. We quantify the behavior of the density of states at the
Fermi level and the short and long range antiferromagnetism as functions of the
distance from the interface and with different interaction strength,
temperature and hopping across the interface. Induced metallic behavior into
the insulator is evident over several lattice spacings, whereas
antiferromagnetic correlations remain small on the metallic side. At large
interface hopping, singlets form between the two boundary layers, shielding the
two systems from each other.Comment: 7 pages, 6 figure
Nature of the quantum phase transitions in the two-dimensional hardcore boson model
We use two Quantum Monte Carlo algorithms to map out the phase diagram of the
two-dimensional hardcore boson Hubbard model with near () and next near
() neighbor repulsion. At half filling we find three phases: Superfluid
(SF), checkerboard solid and striped solid depending on the relative values of
, and the kinetic energy. Doping away from half filling, the
checkerboard solid undergoes phase separation: The superfluid and solid phases
co-exist but not as a single thermodynamic phase. As a function of doping, the
transition from the checkerboard solid is therefore first order. In contrast,
doping the striped solid away from half filling instead produces a striped
supersolid phase: Co-existence of density order with superfluidity as a single
phase. One surprising result is that the entire line of transitions between the
SF and checkerboard solid phases at half filling appears to exhibit dynamical
O(3) symmetry restoration. The transitions appear to be in the same
universality class as the special Heisenberg point even though this symmetry is
explicitly broken by the interaction.Comment: 10 pages, 14 eps figures, include
Dominant charge-density-wave correlations in the Holstein model on the half-filled square lattice
We use an unbiased, continuous-time quantum Monte Carlo method to address the
possibility of a zero-temperature phase without charge-density-wave (CDW) order
in the Holstein and, by extension, the Holstein-Hubbard model on the
half-filled square lattice. In particular, we present results spanning the
whole range of phonon frequencies, allowing us to use the well understood
adiabatic and antiadiabatic limits as reference points. For all parameters
considered, our data suggest that CDW correlations are stronger than pairing
correlations even at very low temperatures. These findings are compatible with
a CDW ground state that is also suggested by theoretical arguments.Comment: 8 pages, 7 figure
Center Vortices at Strong Couplings
A long-range effective action is derived for strong-coupling lattice SU(2)
gauge theory in D=3 dimensions. It is shown that center vortices emerge as
stable saddlepoints of this action.Comment: Lattice 2000 (Topology and Vacuum), 4 page
Time of flight observables and the formation of Mott domains of fermions and bosons on optical lattices
We study, using quantum Monte Carlo simulations, the energetics of the
formation of Mott domains of fermions and bosons trapped on one-dimensional
lattices. We show that, in both cases, the sum of kinetic and interaction
energies exhibits minima when Mott domains appear in the trap. In addition, we
examine the derivatives of the kinetic and interaction energies, and of their
sum, which display clear signatures of the Mott transition. We discuss the
relevance of these findings to time-of-flight experiments that could allow the
detection of the metal--Mott-insulator transition in confined fermions on
optical lattices, and support established results on the
superfluid--Mott-insulator transition in confined bosons on optical lattices.Comment: 5 pages, 6 figures, published versio
Supersolid phases in the one dimensional extended soft core Bosonic Hubbard model
We present results of Quantum Monte Carlo simulations for the soft core
extended bosonic Hubbard model in one dimension exhibiting the presence of
supersolid phases similar to those recently found in two dimensions. We find
that in one and two dimensions, the insulator-supersolid transition has dynamic
critical exponent z=2 whereas the first order insulator-superfluid transition
in two dimensions is replaced by a continuous transition with z=1 in one
dimension. We present evidence that this transition is in the
Kosterlitz-Thouless universality class and discuss the mechanism behind this
difference. The simultaneous presence of two types of quasi long range order
results in two soliton-like dips in the excitation spectrum.Comment: 4 pages, 5 figure
A Generalization of Metropolis and Heat-Bath Sampling for Monte Carlo Simulations
For a wide class of applications of the Monte Carlo method, we describe a
general sampling methodology that is guaranteed to converge to a specified
equilibrium distribution function. The method is distinct from that of
Metropolis in that it is sometimes possible to arrange for unconditional
acceptance of trial moves. It involves sampling states in a local region of
phase space with probability equal to, in the first approximation, the square
root of the desired global probability density function. The validity of this
choice is derived from the Chapman-Kolmogorov equation, and the utility of the
method is illustrated by a prototypical numerical experiment.Comment: RevTeX, 7 pages, 2 table
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
Current Distribution in the Three-Dimensional Random Resistor Network at the Percolation Threshold
We study the multifractal properties of the current distribution of the
three-dimensional random resistor network at the percolation threshold. For
lattices ranging in size from to we measure the second, fourth and
sixth moments of the current distribution, finding {\it e.g.\/} that
where is the conductivity exponent and is the
correlation length exponent.Comment: 10 pages, latex, 8 figures in separate uuencoded fil
Finite temperature QMC study of the one-dimensional polarized Fermi gas
Quantum Monte Carlo (QMC) techniques are used to provide an
approximation-free investigation of the phases of the one-dimensional
attractive Hubbard Hamiltonian in the presence of population imbalance. The
temperature at which the "Fulde-Ferrell-Larkin-Ovchinnikov" (FFLO) phase is
destroyed by thermal fluctuations is determined as a function of the
polarization. It is shown that the presence of a confining potential does not
dramatically alter the FFLO regime, and that recent experiments on trapped
atomic gases likely lie just within the stable temperature range.Comment: 10 pages, 13 figures We added a discussion of the behaviour of the
FFLO peak as a function of the attractive interaction strengt
- …