502 research outputs found
Density functional study of two-dimensional He-4 clusters
Binding energies and density profiles of two-dimensional systems of liquid
He-4 with different geometries are studied by means of a zero-range density
functional adjusted to reproduce the line tension obtained in a previous
diffusion Monte Carlo calculation (lambda_{DMC}=0.121 K/A). It is shown that
this density functional provides accurate results for the binding energy of
large clusters with a reasonable computational effort.Comment: RevTeX4, 11 pages + 2 tables + 6 figure
Dynamic Structure Function in 3he-4he Mixtures
Relevant features of the dynamic structure function in
He-He mixtures at zero temperature are investigated starting from known
properties of the ground state. Sum rules are used to fix rigorous constraints
to the different contributions to , coming from He and He
elementary excitations, as well as to explore the role of the cross term
. Both the low- (phonon-roton He excitations and
1p-1h He excitations) and high- (deep inelastic scattering) ranges are
discussed.Comment: 29 pages, Plain TeX, 11 figures available by request from
[email protected]
Macroscopic dynamics of a trapped Bose-Einstein condensate in the presence of 1D and 2D optical lattices
The hydrodynamic equations of superfluids for a weakly interacting Bose gas
are generalized to include the effects of periodic optical potentials produced
by stationary laser beams. The new equations are characterized by a
renormalized interaction coupling constant and by an effective mass accounting
for the inertia of the system along the laser direction. For large laser
intensities the effective mass is directly related to the tunneling rate
between two consecutive wells. The predictions for the frequencies of the
collective modes of a condensate confined by a magnetic harmonic trap are
discussed for both 1D and 2D optical lattices and compared with recent
experimental data.Comment: 4 pages, 2 postscript figure
Effects of Disorder in a Dilute Bose Gas
We discuss the effects of a weak random external potential on the properties
of the dilute Bose gas at zero temperature. The results recently obtained by
Huang and Meng for the depletion of the condensate and of the superfluid
density are recovered. Results for the shift of the velocity of sound as well
as for its damping due to collisions with the external field are presented. The
damping of phonons is calculated also for dense superfluids. (submitted to
Phys.Rev.B)Comment: 21 pages, Plain Tex, 2 figures available upon request, preprint UTF
31
Scissors mode and superfluidity of a trapped Bose-Einstein condensed gas
We investigate the oscillation of a dilute atomic gas generated by a sudden
rotation of the confining trap (scissors mode). This oscillation reveals the
effects of superfluidity exhibited by a Bose-Einstein condensate. The scissors
mode is investigated also in a classical gas above T_c in various collisional
regimes. The crucial difference with respect to the superfluid case arises from
the occurence of low frequency components, which are responsible for the rigid
value of the moment of inertia. Different experimental procedures to excite the
scissors mode are discussed.Comment: 4 pages, 3 figure
Finite temperature effects in light scattering off Cooper-paired Fermi atoms
We study stimulated light scattering off a superfluid Fermi gas of atoms at
finite temperature. We derive response function that takes into account vertex
correction due to final state interactions; and analyze finite temperature
effects on collective and quasiparticle excitations of a uniform superfluid
Fermi gas. Light polarization is shown to play an important role in
excitations. Our results suggest that it is possible to excite
Bogoliubov-Anderson phonon at a large scattering length by light scattering.Comment: 18 pages, 4 figures, Accepted in J. Phys. B: At. Mol. & Opt. Phy
Vortex signatures in annular Bose-Einstein condensates
We consider a Bose-Einstein condensate confined in a ``Mexican hat''
potential, with a quartic minus quadratic radial dependence. We find conditions
under which the ground state is annular in shape, with a hole in the center of
the condensate. Rotation leads to the appearance of stable multiply-quantized
vortices, giving rise to a superfluid flow around the ring. The collective
modes of the system are explored both numerically and analytically using the
Gross-Pitaevskii and hydrodynamic equations. Potential experimental schemes to
detect vorticity are proposed and evaluated, which include measuring the
splitting of collective mode frequencies, observing expansion following release
from the trap, and probing the momentum distribution of the condensate.Comment: 11 pages, 7 figure
Curvature effects on the surface thickness and tension at the free interface of He systems
The thickness and the surface energy at the free interface of
superfluid He are studied. Results of calculations carried out by using
density functionals for cylindrical and spherical systems are presented in a
unified way, including a comparison with the behavior of planar slabs. It is
found that for large species is independent of the geometry. The obtained
values of are compared with prior theoretical results and experimental
data. Experimental data favor results evaluated by adopting finite range
approaches. The behavior of and exhibit overshoots
similar to that found previously for the central density, the trend of these
observables towards their asymptotic values is examined.Comment: 35 pages, TeX, 5 figures, definitive versio
Fermi Gases in Slowly Rotating Traps: Superfluid vs Collisional Hydrodynamics
The dynamic behavior of a Fermi gas confined in a deformed trap rotating at
low angular velocity is investigated in the framework of hydrodynamic theory.
The differences exhibited by a normal gas in the collisional regime and a
superfluid are discussed. Special emphasis is given to the collective
oscillations excited when the deformation of the rotating trap is suddenly
removed or when the rotation is suddenly stopped. The presence of vorticity in
the normal phase is shown to give rise to precession and beating phenomena
which are absent in the superfluid phase.Comment: 4 pages, 2 figure
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