270 research outputs found
One-dimensional two-component fermions with contact even-wave repulsion and SU(2) breaking near-resonant odd-wave attraction
We consider a one-dimensional (1D) two-component atomic Fermi gas with
contact interaction in the even-wave channel (Yang-Gaudin model) and study the
effect of an SU(2) symmetry breaking near-resonant odd-wave interaction within
one of the components. Starting from the microscopic Hamiltonian, we derive an
effective field theory for the spin degrees of freedom using the bosonization
technique. It is shown that at a critical value of the odd-wave interaction
there is a first-order phase transition from a phase with zero total spin and
zero magnetization to the spin-segregated phase where the magnetization locally
differs from zero.Comment: 18 pages, 3 fugures; references adde
Finite size effects for the gap in the excitation spectrum of the one-dimensional Hubbard model
We study finite size effects for the gap of the quasiparticle excitation
spectrum in the weakly interacting regime one-dimensional Hubbard model with
on-site attraction. Two type of corrections to the result of the thermodynamic
limit are obtained. Aside from a power law (conformal) correction due to
gapless excitations which behaves as , where is the number of
lattice sites, we obtain corrections related to the existence of gapped
excitations. First of all, there is an exponential correction which in the
weakly interacting regime () behaves as in the extreme limit of ,
where is the hopping amplitude, is the on-site energy, and
is the gap in the thermodynamic limit. Second, in a finite
size system a spin-flip producing unpaired fermions leads to the appearance of
solitons with non-zero momenta, which provides an extra (non-exponential)
contribution . For moderate but still large values of
, these corrections significantly increase and may
become comparable with the conformal correction. Moreover, in the case
of weak interactions where , the exponential correction
exceeds higher order power law corrections in a wide range of parameters,
namely for , and so does
even in a wider range of . For sufficiently small number of particles,
which can be of the order of thousands in the weakly interacting regime, the
gap is fully dominated by finite size effects.Comment: 17 pages, 5 figure
Scattering properties of weakly bound dimers of fermionic atoms
We consider weakly bound diatomic molecules (dimers) formed in a
two-component atomic Fermi gas with a large positive scattering length for the
interspecies interaction. We develop a theoretical approach for calculating
atom-dimer and dimer-dimer elastic scattering and for analyzing the inelastic
collisional relaxation of the molecules into deep bound states. This approach
is based on the single-channel zero range approximation, and we find that it is
applicable in the vicinity of a wide two-body Feshbach resonance. Our results
draw prospects for various interesting manipulations of weakly bound dimers of
fermionic atoms.Comment: extended version of cond-mat/030901
Zero sound in a two-dimensional dipolar Fermi gas
We study zero sound in a weakly interacting 2D gas of single-component
fermionic dipoles (polar molecules or atoms with a large magnetic moment)
tilted with respect to the plane of their translational motion. It is shown
that the propagation of zero sound is provided by both mean field and many-body
(beyond mean field) effects, and the anisotropy of the sound velocity is the
same as the one of the Fermi velocity. The damping of zero sound modes can be
much slower than that of quasiparticle excitations of the same energy. One thus
has wide possibilities for the observation of zero sound modes in experiments
with 2D fermionic dipoles, although the zero sound peak in the structure
function is very close to the particle-hole continuum.Comment: 15 pages, 2 figure
Stable dilute supersolid of two-dimensional dipolar bosons
We consider two-dimensional bosonic dipoles oriented perpendicularly to the
plane. On top of the usual two-body contact and long-range dipolar interactions
we add a contact three-body repulsion as expected, in particular, for dipoles
in the bilayer geometry with tunneling. The three-body repulsion is crucial for
stabilizing the system, and we show that our model allows for stable continuous
space supersolid states in the dilute regime and calculate the zero-temperature
phase diagram.Comment: revised version, 5 pages, 2 figures, with 3 pages supplementary
materia
Vortex structures in rotating Bose-Einstein condensates
We present an analytical solution for the vortex lattice in a rapidly
rotating trapped Bose-Einstein condensate (BEC) in the lowest Landau level and
discuss deviations from the Thomas-Fermi density profile. This solution is
exact in the limit of a large number of vortices and is obtained for the cases
of circularly symmetric and narrow channel geometries. The latter is realized
when the trapping frequencies in the plane perpendicular to the rotation axis
are different from each other and the rotation frequency is equal to the
smallest of them. This leads to the cancelation of the trapping potential in
the direction of the weaker confinement and makes the system infinitely
elongated in this direction. For this case we calculate the phase diagram as a
function of the interaction strength and rotation frequency and identify the
order of quantum phase transitions between the states with a different number
of vortex rows.Comment: 17 pages, 12 figures, with addition
Feshbach resonances in Cesium at Ultra-low Static Magnetic Fields
We have observed Feshbach resonances for 133Cs atoms in two different
hyperfine states at ultra-low static magnetic fields by using an atomic
fountain clock. The extreme sensitivity of our setup allows for high
signal-to-noise-ratio observations at densities of only 2*10^7 cm^{-3}. We have
reproduced these resonances using coupled-channels calculations which are in
excellent agreement with our measurements. We justify that these are s-wave
resonances involving weakly-bound states of the triplet molecular Hamiltonian,
identify the resonant closed channels, and explain the observed multi-peak
structure. We also describe a model which precisely accounts for the
collisional processes in the fountain and which explains the asymmetric shape
of the observed Feshbach resonances in the regime where the kinetic energy
dominates over the coupling strength.Comment: 5 pages, 4 figures, 1 tabl
Crystalline phase of strongly interacting Fermi mixtures
We show that the system of weakly bound molecules of heavy and light
fermionic atoms is characterized by a long-range intermolecular repulsion and
can undergo a gas-crystal quantum transition if the mass ratio exceeds a
critical value. For the critical mass ratio above 100 obtained in our
calculations, this crystalline order can be observed as a superlattice in an
optical lattice for heavy atoms with a small filling factor. We also find that
this novel system is sufficiently stable with respect to molecular relaxation
into deep bound states and to the process of trimer formation.Comment: 4 pages, 1 color figure, published versio
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