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Title: Superfluid stability in the BEC-BCS crossover

Abstract

We consider a dilute atomic gas of two species of fermions with unequal concentrations under a Feshbach resonance. We find that the system can have distinct properties due to the unbound fermions. The uniform state is stable only when either (a) beyond a critical coupling strength, where it is a gapless superfluid, or (b) when the coupling strength is sufficiently weak, where it is a normal Fermi gas mixture. Phase transition(s) must therefore occur when the resonance is crossed, in contrast to the equal population case where a smooth crossover takes place.

Authors:
; ;  [1];  [2]
  1. Department of Physics, National Chung Cheng University, Chiayi 621, Taiwan (China)
  2. (China)
Publication Date:
OSTI Identifier:
20788034
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review. B, Condensed Matter and Materials Physics; Journal Volume: 73; Journal Issue: 13; Other Information: DOI: 10.1103/PhysRevB.73.132506; (c) 2006 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; 71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; BCS THEORY; BOSE-EINSTEIN CONDENSATION; COUPLING; FERMI GAS; FERMIONS; MIXTURES; PHASE TRANSFORMATIONS; RESONANCE; STABILITY; SUPERFLUIDITY

Citation Formats

Pao, C.-H., Wu, S.-T., Yip, S.-K., and Institute of Physics, Academia Sinica, Nankang, Taipei 115, Taiwan. Superfluid stability in the BEC-BCS crossover. United States: N. p., 2006. Web. doi:10.1103/PHYSREVB.73.1.
Pao, C.-H., Wu, S.-T., Yip, S.-K., & Institute of Physics, Academia Sinica, Nankang, Taipei 115, Taiwan. Superfluid stability in the BEC-BCS crossover. United States. doi:10.1103/PHYSREVB.73.1.
Pao, C.-H., Wu, S.-T., Yip, S.-K., and Institute of Physics, Academia Sinica, Nankang, Taipei 115, Taiwan. Sat . "Superfluid stability in the BEC-BCS crossover". United States. doi:10.1103/PHYSREVB.73.1.
@article{osti_20788034,
title = {Superfluid stability in the BEC-BCS crossover},
author = {Pao, C.-H. and Wu, S.-T. and Yip, S.-K. and Institute of Physics, Academia Sinica, Nankang, Taipei 115, Taiwan},
abstractNote = {We consider a dilute atomic gas of two species of fermions with unequal concentrations under a Feshbach resonance. We find that the system can have distinct properties due to the unbound fermions. The uniform state is stable only when either (a) beyond a critical coupling strength, where it is a gapless superfluid, or (b) when the coupling strength is sufficiently weak, where it is a normal Fermi gas mixture. Phase transition(s) must therefore occur when the resonance is crossed, in contrast to the equal population case where a smooth crossover takes place.},
doi = {10.1103/PHYSREVB.73.1},
journal = {Physical Review. B, Condensed Matter and Materials Physics},
number = 13,
volume = 73,
place = {United States},
year = {Sat Apr 01 00:00:00 EST 2006},
month = {Sat Apr 01 00:00:00 EST 2006}
}
  • No abstract prepared.
  • We point out an error in recent work by Pao, Wu, and Yip [Phys. Rev. B 73, 132506 (2006)], that stems from their use of a necessary but not sufficient condition [positive compressibility (magnetic susceptibility) and superfluid stiffness] for the stability of the ground state of a polarized Fermi gas. As a result, for a range of detunings their proposed ground-state solution is a local maximum rather than a minimum of the ground state energy, which thereby invalidates their proposed phase diagram for resonantly interacting fermions under an imposed population difference.
  • We investigate single-particle excitations and strong-coupling effects in the BCS-BEC crossover regime of a superfluid Fermi gas. Including phase and amplitude fluctuations of the superfluid order parameter within a T-matrix theory, we calculate the superfluid density of states (DOS), as well as single-particle spectral weight, over the entire BCS-BEC crossover region below the superfluid transition temperature T{sub c}. We clarify how the pseudogap in the normal state evolves into the superfluid gap, as one passes through T{sub c}. While the pseudogap in DOS continuously evolves into the superfluid gap in the weak-coupling BCS regime, the superfluid gap in the crossovermore » region is shown to appear in DOS after the pseudogap disappears below T{sub c}. In the phase diagram with respect to the temperature and interaction strength, we determine the region where strong pairing fluctuations dominate over single-particle properties of the system. Our results would be useful for the study of strong-coupling phenomena in the BCS-BEC crossover regime of a superfluid Fermi gas.« less
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  • We have analyzed a single vortex at T=0 in a 3D superfluid atomic Fermi gas across a Feshbach resonance. On the BCS side, the order parameter varies on two scales: k{sub F}{sup -1} and the coherence length {xi}, while only variation on the scale of {xi} is seen away from the BCS limit. The circulating current has a peak value j{sub max} which is a nonmonotonic function of 1/k{sub F}a{sub s} implying a maximum critical velocity {approx}v{sub F} at unitarity. The number of fermionic bound states in the core decreases as we move from the BCS to the BEC regime.more » Remarkably, a bound state branch persists even on the BEC side reflecting the composite nature of bosonic molecules.« less