937 research outputs found
Ultracold atoms in one-dimensional optical lattices approaching the Tonks-Girardeau regime
Recent experiments on ultracold atomic alkali gases in a one-dimensional
optical lattice have demonstrated the transition from a gas of soft-core bosons
to a Tonks-Girardeau gas in the hard-core limit, where one-dimensional bosons
behave like fermions in many respects. We have studied the underlying many-body
physics through numerical simulations which accommodate both the soft-core and
hard-core limits in one single framework. We find that the Tonks-Girardeau gas
is reached only at the strongest optical lattice potentials. Results for
slightly higher densities, where the gas develops a Mott-like phase already at
weaker optical lattice potentials, show that these Mott-like short range
correlations do not enhance the convergence to the hard-core limit.Comment: 4 pages, 3 figures, replaced with published versio
Supersolid phase with cold polar molecules on a triangular lattice
We study a system of heteronuclear molecules on a triangular lattice and
analyze the potential of this system for the experimental realization of a
supersolid phase. The ground state phase diagram contains superfluid, solid and
supersolid phases. At finite temperatures and strong interactions there is an
additional emulsion region, in contrast to similar models with short-range
interactions. We derive the maximal critical temperature and the
corresponding entropy for supersolidity and find feasible
experimental conditions for its realization.Comment: 4 pages, 4 figure
The SHARE survey: presentation and first results for the French edition
The SHARE survey (Survey on Health Ageing and Retirement in Europe) is an international and multidisciplinary operation launched in 2002, led by a European network coordinated by the MEA of the University of Mannheim. Its ambition is to become an instrument of reference for interdisciplinary research on ageing. A test of this survey on approximately 12000 households took place in 10 European countries in 2004. This first wave already allows the realization of comparative work on participating countries, either descriptive or microeconometric. Data have been made available to researchers in spring 2005, after publication of a volume of first results. This article presents the survey and gives an outline of its potentialities, using some first descriptive results for France.Ageing, health, pensions
Maximum occupation number for composite boson states
One of the major differences between fermions and bosons is that fermionic
states have a maximum occupation number of one, whereas the occupation number
for bosonic states is in principle unlimited. For bosons that are made up of
fermions, one could ask the question to what extent the Pauli principle for the
constituent fermions would limit the boson occupation number. Intuitively one
can expect the maximum occupation number to be proportional to the available
volume for the bosons divided by the volume occupied by the fermions inside one
boson, though a rigorous derivation of this result has not been given before.
In this letter we show how the maximum occupation number can be calculated from
the ground-state energy of a fermionic generalized pairing problem. A very
accurate analytical estimate of this eigenvalue is derived. From that a general
expression is obtained for the maximum occupation number of a composite boson
state, based solely on the intrinsic fermionic structure of the bosons. The
consequences for Bose-Einstein condensates of excitons in semiconductors and
ultra cold trapped atoms are discussed.Comment: 4 pages, Revte
Out-Group Mating Threat and Disease Threat Increase Implicit Negative Attitudes Toward the Out-Group Among Men
We investigated if perceiving an out-group as a threat to one's mating opportunities enhanced the implicit negative attitudes toward that out-group. In addition, we examined the moderating effect of disease threat on the relationship between an out-group mating threat and implicit negative attitudes toward that out-group. In Experiment 1, an out-group mating threat led to stronger implicit negative out-group attitudes as measured by the Implicit Association Test, but only for men with high chronic perceived vulnerability to disease. No such effects were found among women. In Experiment 2, men in the out-group mating threat condition who were primed with disease prevalence showed significantly stronger implicit negative attitudes toward the out-group than controls. Findings are discussed with reference to the functional approach to prejudice and sex-specific motivational reactions to different out-group threats
Quantum Monte Carlo simulation in the canonical ensemble at finite temperature
A quantum Monte Carlo method with non-local update scheme is presented. The
method is based on a path-integral decomposition and a worm operator which is
local in imaginary time. It generates states with a fixed number of particles
and respects other exact symmetries. Observables like the equal-time Green's
function can be evaluated in an efficient way. To demonstrate the versatility
of the method, results for the one-dimensional Bose-Hubbard model and a nuclear
pairing model are presented. Within the context of the Bose-Hubbard model the
efficiency of the algorithm is discussed.Comment: 11 pages, 8 figure
Stochastic Mean-Field Theory for the Disordered Bose-Hubbard Model
We investigate the effect of diagonal disorder on bosons in an optical
lattice described by an Anderson-Hubbard model at zero temperature. It is known
that within Gutzwiller mean-field theory spatially resolved calculations suffer
particularly from finite system sizes in the disordered case, while arithmetic
averaging of the order parameter cannot describe the Bose glass phase for
finite hopping . Here we present and apply a new \emph{stochastic}
mean-field theory which captures localization due to disorder, includes
non-trivial dimensional effects beyond the mean-field scaling level and is
applicable in the thermodynamic limit. In contrast to fermionic systems, we
find the existence of a critical hopping strength, above which the system
remains superfluid for arbitrarily strong disorder.Comment: 6 pages, 6 figure
The Classical Heisenberg Model on the Centred Pyrochlore Lattice
The centred pyrochlore lattice is a novel geometrically frustrated lattice,
realized in the metal-organic framework Mn(ta) (arXiv:2203.08780) where the
basic unit of spins is a five site centred tetrahedron. Here, we present an
in-depth theoretical study of the classical Heisenberg model on this
lattice, using a combination of mean-field analytical methods and Monte Carlo
simulations. We find a rich phase diagram with low temperature states
exhibiting ferrimagnetic order, partial ordering, and a highly degenerate spin
liquid with distinct regimes of low temperature correlations. We discuss in
detail how the regime displaying broadened pinch points in its spin structure
factor is consistent with an effective description in terms of a fluid of
interacting charges. We also show how this picture holds in two dimensions on
the analogous centred kagome lattice and elucidate the connection to the
physics of thin films in () dimensions. Furthermore, we show that a
Coulomb phase can be stabilized on the centred pyrochlore lattice by the
addition of further neighbour couplings. This demonstrates the centred
pyrochlore lattice is an experimentally relevant geometry which naturally hosts
emergent gauge fields in the presence of charges at low energies.Comment: 29 pages, 9 figures, resubmission to SciPost with minor revision
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