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Title: Comment on 'Superfluid stability in the BEC-BCS crossover'

Abstract

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.

Authors:
;  [1]
  1. Department of Physics, University of Colorado, Boulder, Colorado 80309 (United States)
Publication Date:
OSTI Identifier:
20957793
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review. B, Condensed Matter and Materials Physics; Journal Volume: 75; Journal Issue: 13; Other Information: DOI: 10.1103/PhysRevB.75.136501; (c) 2007 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; FERMI GAS; FERMIONS; FLEXIBILITY; GROUND STATES; MAGNETIC SUSCEPTIBILITY; MATHEMATICAL SOLUTIONS; PHASE DIAGRAMS; SUPERFLUIDITY

Citation Formats

Sheehy, Daniel E., and Radzihovsky, Leo. Comment on 'Superfluid stability in the BEC-BCS crossover'. United States: N. p., 2007. Web. doi:10.1103/PHYSREVB.75.136501.
Sheehy, Daniel E., & Radzihovsky, Leo. Comment on 'Superfluid stability in the BEC-BCS crossover'. United States. doi:10.1103/PHYSREVB.75.136501.
Sheehy, Daniel E., and Radzihovsky, Leo. Sun . "Comment on 'Superfluid stability in the BEC-BCS crossover'". United States. doi:10.1103/PHYSREVB.75.136501.
@article{osti_20957793,
title = {Comment on 'Superfluid stability in the BEC-BCS crossover'},
author = {Sheehy, Daniel E. and Radzihovsky, Leo},
abstractNote = {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.},
doi = {10.1103/PHYSREVB.75.136501},
journal = {Physical Review. B, Condensed Matter and Materials Physics},
number = 13,
volume = 75,
place = {United States},
year = {Sun Apr 01 00:00:00 EDT 2007},
month = {Sun Apr 01 00:00:00 EDT 2007}
}
  • The work by T. K. Ghosh and K. Machida [Phys. Rev. A 73, 013613 (2006) and cond-mat/0510160] on the sound velocity in a cylindrically confined Fermi superfluid obeying a power-law equation of state is shown to make use of an improper projection of the sound wave equation. This inaccuracy fully accounts for the difference between their results and those previously reported by Capuzzi et al. [Phys. Rev. A 73, 021603(R) (2006) and cond-mat/0509323]. In this Comment, we show that both approaches lead exactly to the same result when the correct weight function is used in the projection. Plots of themore » correct behavior of the phonon and monopole-mode spectra in the BCS and unitary limits and in the BEC regime are also shown.« less
  • We are providing a Reply to the preceding Comment.
  • 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.
  • No abstract prepared.
  • 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