4,038 research outputs found
The BCS-BEC Crossover
This chapter presents the crossover from the Bardeen-Cooper-Schrieffer (BCS)
state of weakly-correlated pairs of fermions to the Bose-Einstein condensation
(BEC) of diatomic molecules in the atomic Fermi gas. Our aim is to provide a
pedagogical review of the BCS-BEC crossover, with an emphasis on the basic
concepts, particularly those that are not generally known or are difficult to
find in the literature. We shall not attempt to give an exhaustive survey of
current research in the limited space here; where possible, we will direct the
reader to more extensive reviews.Comment: 19 pages, 6 figures. This article will be published as Chapter 9 in
"Quantum gas experiments - exploring many-body states", edited by P. Torma
and K. Sengstock, Imperial College Press, London, to be published 201
Three-body correlations in a two-dimensional SU(3) Fermi gas
We consider a three-component Fermi gas that has SU(3) symmetry and is
confined to two dimensions (2D). For realistic cold atomic gas experiments, we
show that the phase diagram of the quasi-2D system can be characterized using
two 2D scattering parameters: the scattering length and the effective range.
Unlike the case in 3D, we argue that three-body bound states (trimers) in the
quasi-2D system can be stable against three-body losses. Using a low-density
expansion coupled with a variational approach, we investigate the fate of such
trimers in the many-body system as the attractive interactions are decreased
(or, conversely, as the density of particles is increased). We find that
remnants of trimers can persist in the form of strong three-body correlations
in the weak-coupling (high-density) limit.Comment: 13 pages, 4 figure
Dipolar fermions in a multilayer geometry
We investigate the behavior of identical dipolar fermions with aligned dipole
moments in two-dimensional multilayers at zero temperature. We consider density
instabilities that are driven by the attractive part of the dipolar interaction
and, for the case of bilayers, we elucidate the properties of the stripe phase
recently predicted to exist in this interaction regime. When the number of
layers is increased, we find that this "attractive" stripe phase exists for an
increasingly larger range of dipole angles, and if the interlayer distance is
sufficiently small, the stripe phase eventually spans the full range of angles,
including the situation where the dipole moments are aligned perpendicular to
the planes. In the limit of an infinite number of layers, we derive an analytic
expression for the interlayer effects in the density-density response function
and, using this result, we find that the stripe phase is replaced by a collapse
of the dipolar system.Comment: 9 pages, 8 figure
Evaporative depolarization and spin transport in a unitary trapped Fermi gas
We consider a partially spin-polarized atomic Fermi gas in a
high-aspect-ratio trap, with a flux of predominantly spin-up atoms exiting the
center of the trap. We argue that such a scenario can be produced by
evaporative cooling, and we find that it can result in a substantially
non-equilibrium polarization pattern for typical experimental parameters. We
offer this as a possible explanation for the quantitative discrepancies in
recent experiments on spin-imbalanced unitary Fermi gases.Comment: 6 pages, 3 figures; published versio
Density-wave phases of dipolar fermions in a bilayer
We investigate the phase diagram of dipolar fermions with aligned dipole
moments in a two-dimensional (2D) bilayer. Using a version of the
Singwi-Tosi-Land-Sjolander scheme recently adapted to dipolar fermions in a
single layer [M. M. Parish and F. M. Marchetti, Phys. Rev. Lett. 108, 145304
(2012)], we determine the density-wave instabilities of the bilayer system
within linear response theory. We find that the bilayer geometry can stabilize
the collapse of the 2D dipolar Fermi gas with intralayer attraction to form a
new density wave phase that has an orientation perpendicular to the density
wave expected for strong intralayer repulsion. We thus obtain a quantum phase
transition between stripe phases that is driven by the interplay between strong
correlations and the architecture of the low dimensional system.Comment: 5 pages, 3 figure
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