10,955 research outputs found

### Momentum-resolved radio-frequency spectroscopy of ultracold atomic Fermi gases in a spin-orbit coupled lattice

We investigate theoretically momentum-resolved radio-frequency (rf)
spectroscopy of a noninteracting atomic Fermi gas in a spin-orbit coupled
lattice. This lattice configuration has been recently created at MIT [Cheuk et
al., arXiv:1205.3483] for 6Li atoms, by coupling the two hyperfine spin-states
with a pair of Raman laser beams and additional rf coupling. Here, we show that
momentum-resolved rf spectroscopy can measure single-particle energies and
eigenstates and therefore resolve the band structure of the spin-orbit coupled
lattice. In our calculations, we take into account the effects of temperatures
and harmonic traps. Our predictions are to be confronted with future
experiments on spin-orbit coupled Fermi gases of 40K atoms in a lattice
potential.Comment: 9 pages, 8 figure

### Impurity probe of topological superfluid in one-dimensional spin-orbit coupled atomic Fermi gases

We investigate theoretically non-magnetic impurity scattering in a
one-dimensional atomic topological superfluid in harmonic traps, by solving
self-consistently the microscopic Bogoliubov-de Gennes equation. In sharp
contrast to topologically trivial Bardeen-Cooper-Schrieffer \textit{s}-wave
superfluid, topological superfluid can host a mid-gap state that is bound to
localized non-magnetic impurity. For strong impurity scattering, the bound
state becomes universal, with nearly zero energy and a wave-function that
closely follows the symmetry of that of Majorana fermions. We propose that the
observation of such a universal bound state could be a useful evidence for
characterizing the topolgoical nature of topological superfluids. Our
prediction is applicable to an ultracold resonantly-interacting Fermi gas of
$^{40}$K atoms with spin-orbit coupling confined in a two-dimensional optical
lattice.Comment: 9 pages, 8 figure

### Fulde-Ferrell pairing instability of a Rashba spin-orbit coupled Fermi gas

We theoretically analyze the pairing instability of a three-dimensional
ultracold atomic Fermi gas towards a Fulde-Ferrell superfluid, in the presence
of Rashba spin-orbit coupling and in-plane Zeeman field. We use the standard
Thouless criterion for the onset of superfluidity, with which the effect of
pair fluctuations is partially taken into account by approximately using a
mean-field chemical potential at zero temperature. This gives rise to an
improved prediction of the superfluid transition temperature beyond mean-field,
particularly in the strong-coupling unitary limit. We also investigate the
pairing instability with increasing Rashba spin-orbit coupling, along the
crossover from a Bardeen-Cooper-Schrieffer superfluid to a Bose-Einstein
condensate of Rashbons (i.e., the tightly bound state of two fermions formed by
strong Rashba spin-orbit couplingComment: 8 pages, 9 figure

### A self-consistent theory of atomic Fermi gases with a Feshbach resonance at the superfluid transition

A self-consistent theory is derived to describe the BCS-BEC crossover for a
strongly interacting Fermi gas with a Feshbach resonance. In the theory the
fluctuation of the dressed molecules, consisting of both preformed Cooper-pairs
and ``bare'' Feshbach molecules, has been included within a self-consistent
$T$-matrix approximation, beyond the Nozi\`{e}res and Schmitt-Rink strategy
considered by Ohashi and Griffin. The resulting self-consistent equations are
solved numerically to investigate the normal state properties of the crossover
at various resonance widths. It is found that the superfluid transition
temperature $T_c$ increases monotonically at all widths as the effective
interaction between atoms becomes more attractive. Furthermore, a residue
factor $Z_m$ of the molecule's Green function and a complex effective mass have
been determined, to characterize the fraction and lifetime of Feshbach
molecules at $T_c$. Our many-body calculations of $Z_m$ agree qualitatively
well with the recent measurments on the gas of $^6$Li atoms near the broad
resonance at 834 Gauss. The crossover from narrow to broad resonances has also
been studied.Comment: 6 papes, 6 figure

### Topological superfluid in one-dimensional spin-orbit coupled atomic Fermi gases

ARC Centre of Excellence for Quantum-Atom Optics, Centre for Atom Optics and
Ultrafast Spectroscopy, Swinburne University of Technology, Melbourne 3122,
AustraliaComment: 7 pages, 8 figures; submitted to Physical Review

### Collective mode evidence of high-spin bosonization in a trapped one-dimensional atomic Fermi gas with tunable spin

We calculate the frequency of collective modes of a one-dimensional
repulsively interacting Fermi gas with high-spin symmetry confined in harmonic
traps at zero temperature. This is a system realizable with fermionic
alkaline-earth-metal atoms such as $^{173}$Yb, which displays an exact
SU($\kappa$) spin symmetry with $\kappa\geqslant2$ and behaves like a spinless
interacting Bose gas in the limit of infinite spin components
$\kappa\rightarrow\infty$, namely high-spin bosonization. We solve the
homogeneous equation of state of the high-spin Fermi system by using Bethe
ansatz technique and obtain the density distribution in harmonic traps based on
local density approximation. The frequency of collective modes is calculated by
exactly solving the zero-temperature hydrodynamic equation. In the limit of
large number of spin-components, we show that the mode frequency of the system
approaches to that of a one-dimensional spinless interacting Bose gas, as a
result of high-spin bosonization. Our prediction of collective modes is in
excellent agreement with a very recent measurement for a Fermi gas of
$^{173}$Yb atoms with tunable spin confined in a two-dimensional tight optical
lattice.Comment: 11 pages, 8 figure

### First and second sound in a two-dimensional dilute Bose gas across the Berezinskii-Kosterlitz-Thouless transition

We theoretically investigate first and second sound of a two-dimensional (2D)
atomic Bose gas in harmonic traps by solving Landau's two-fluid hydrodynamic
equations. For an isotropic trap, we find that first and second sound modes
become degenerate at certain temperatures and exhibit typical avoided crossings
in mode frequencies. At these temperatures, second sound has significant
density fluctuation due to its hybridization with first sound and has a
divergent mode frequency towards the Berezinskii-Kosterlitz-Thouless (BKT)
transition. For a highly anisotropic trap, we derive the simplified
one-dimensional hydrodynamic equations and discuss the sound-wave propagation
along the weakly confined direction. Due to the universal jump of the
superfluid density inherent to the BKT transition, we show that the first sound
velocity exhibits a kink across the transition. Our predictions can be readily
examined in current experimental setups for 2D dilute Bose gases.Comment: 5 pages, 4 figure

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