5,779 research outputs found
Short-distance and short-time structure of a unitary Fermi gas
We consider the operator product expansions for unitarity fermions. We
compute the dynamic structure factor S(q,w) at large frequency and wavenumber
away from the one-particle peak. The overall normalization of S(q,w) is
determined by Tan's contact parameter, and the dependence on q and w is
obtained in closed analytic form. We also find energy deposited into the system
by small, rapid variations of the inverse scattering length.Comment: 11 pages, 8 figure
Remnant superfluid collective phase oscillations in the normal state of systems with resonant pairing
The signature of superfluidity in bosonic systems is a sound wave-like
spectrum of the single particle excitations which in the case of strong
interactions is roughly temperature independent. In fermionic systems, where
fermion pairing arises as a resonance phenomenon between free fermions and
paired fermionic states (examples are: the atomic gases of lithium or potassium
controlled by a Feshbach resonance, polaronic systems in the intermediary
coupling regime, d-wave hole pairing in the strongly correlated Hubbard
system), remnants of such superfluid characteristics are expected to be visible
in the normal state. The single particle excitations maintain there a sound
wave like structure for wave vectors above a certain q_{min}(T) where they
practically coincide there with the spectrum of the superfluid phase for
T<T_{c}. Upon approaching the transition from above this region in q-space
extends down to small momenta, except for a narrow region around q=0 where such
modes change into damped free particleComment: 5 pages, 3 figures; to appear in Phys Rev
Vortex structures and zero energy states in the BCS-to-BEC evolution of p-wave resonant Fermi gases
Multiply quantized vortices in the BCS-to-BEC evolution of p-wave resonant
Fermi gases are investigated theoretically. The vortex structure and the
low-energy quasiparticle states are discussed, based on the self-consistent
calculations of the Bogoliubov-de Gennes and gap equations. We reveal the
direct relation between the macroscopic structure of vortices, such as particle
densities, and the low-lying quasiparticle state. In addition, the net angular
momentum for multiply quantized vortices with a vorticity is found to
be expressed by a simple equation, which reflects the chirality of the Cooper
pairing. Hence, the observation of the particle density depletion and the
measurement of the angular momentum will provide the information on the
core-bound state and -wave superfluidity. Moreover, the details on the zero
energy Majorana state are discussed in the vicinity of the BCS-to-BEC
evolution. It is demonstrated numerically that the zero energy Majorana state
appears in the weak coupling BCS limit only when the vortex winding number is
odd. There exist the branches of the core bound states for a vortex
state with vorticity , whereas only one of them can be the zero energy.
This zero energy state vanishes at the BCS-BEC topological phase transition,
because of interference between the core-bound and edge-bound states.Comment: 15 pages, 9 figures, published versio
Toward an AdS/cold atoms correspondence: a geometric realization of the Schroedinger symmetry
We discuss a realization of the nonrelativistic conformal group (the
Schroedinger group) as the symmetry of a spacetime. We write down a toy model
in which this geometry is a solution to field equations. We discuss various
issues related to nonrelativistic holography. In particular, we argue that free
fermions and fermions at unitarity correspond to the same bulk theory with
different choices for the near-boundary asymptotics corresponding to the source
and the expectation value of one operator. We describe an extended version of
nonrelativistic general coordinate invariance which is realized
holographically.Comment: 14 pages; v2: typos fixed, published versio
Crossover temperature of Bose-Einstein condensation in an atomic Fermi gas
We show that in an atomic Fermi gas near a Feshbach resonance the crossover
between a Bose-Einstein condensate of diatomic molecules and a Bose-Einstein
condensate of Cooper pairs occurs at positive detuning, i.e., when the
molecular energy level lies in the two-atom continuum. We determine the
crossover temperature as a function of the applied magnetic field and find
excellent agreement with the experiment of Regal et al. [Phys. Rev. Lett. 92,
040403 (2004)] that has recently observed this crossover temperature.Comment: 4 pages, 2 figure
Atmospheric Analysis of the M/L- and M/T-Dwarf Binary Systems LHS 102 and Gliese 229
We present 0.9-2.5um spectroscopy with R~800 and 1.12-1.22um spectroscopy
with R~5800 for the M dwarfs Gl 229A and LHS 102A, and for the L dwarf LHS
102B. We also report IZJHKL' photometry for both components of the LHS 102
system, and L' photometry for Gl 229A. The data are combined with previously
published spectroscopy and photometry to produce flux distributions for each
component of the kinematically old disk M/L-dwarf binary system LHS 102 and the
kinematically young disk M/T-dwarf binary system Gliese 229. The data are
analyzed using synthetic spectra generated by the latest "AMES-dusty" and
"AMES-cond" models by Allard & Hauschildt. Although the models are not able to
reproduce the overall slope of the infrared flux distribution of the L dwarf,
most likely due to the treatment of dust in the photosphere, the data for the M
dwarfs and the T dwarf are well matched. We find that the Gl 229 system is
metal-poor despite having kinematics of the young disk, and that the LHS 102
system has solar metallicity. The observed luminosities and derived
temperatures and gravities are consistent with evolutionary model predictions
if the Gl 229 system is very young (age ~30 Myr) with masses (A,B) of
(0.38,>0.007)M(sun), and the LHS 102 system is older, aged 1-10 Gyr with masses
(A,B) of (0.19,0.07)M(sun).Comment: 29 pages incl. 13 figures and 5 tables;; accepted for publication in
MNRA
First Order Superfluid to Bose Metal Transition in Systems with Resonant Pairing
Systems showing resonant superfluidity, driven by an exchange coupling of
strength between uncorrelated pairs of itinerant fermions and tightly bound
ones, undergo a first order phase transition as increases beyond some
critical value . The superfluid phase for is characterized by
a gap in the fermionic single particle spectrum and an acoustic sound-wave like
collective mode of the bosonic resonating fermion pairs inside this gap. For
this state gives way to a phase uncorrelated bosonic liquid with a
spectrum.Comment: 5 pages, 3 figure
BCS-BEC crossover in a relativistic boson-fermion model beyond mean field approximation
We investigate the fluctuation effect of the di-fermion field in the
crossover from Bardeen-Cooper-Schrieffer (BCS) pairing to a Bose-Einstein
condensate (BEC) in a relativistic superfluid. We work within the boson-fermion
model obeying a global U(1) symmetry. To go beyond the mean field approximation
we use Cornwall-Jackiw-Tomboulis (CJT) formalism to include higher order
contributions. The quantum fluctuations of the pairing condensate is provided
by bosons in non-zero modes, whose interaction with fermions gives the
two-particle-irreducible (2PI) effective potential. It changes the crossover
property in the BEC regime. With the fluctuations the superfluid phase
transition becomes the first order in grand canonical ensemble. We calculate
the condensate, the critical temperature and particle abundances as
functions of crossover parameter the boson mass.Comment: The model Lagrangian is re-formulated by decomposing the complex
scalar field into its real and imaginary parts. The anomalous propagators of
the complex scalar are then included at tree level. All numerical results are
updated. ReVTex 4, 13 pages, 10 figures, PRD accepted versio
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