Collective excitations of superfluid Fermi gases near the transition temperature

S. N. Klimin, J. Tempere, and H. Kurkjian
Phys. Rev. A 103, 043336 – Published 30 April 2021

Abstract

Studying the collective pairing phenomena in a two-component Fermi gas, we predict the appearance near the transition temperature Tc of a well-resolved collective mode of quadratic dispersion. The mode is visible both above and below Tc in the system's response to a driving pairing field. When approaching Tc from below, the phononic and pair-breaking branches, characteristic of the zero temperature behavior, reduce to a relatively low energy-momentum region. Elsewhere they are replaced by the quadratically dispersed pairing resonance, which thus acts as a precursor of the phase transition. In the strong-coupling and Bose-Einstein condensate regime, this mode is a weakly damped propagating mode associated with a Lorentzian resonance. Conversely, in the BCS limit it is a relaxation mode of pure imaginary eigenenergy. At large momenta, the resonance disappears when it is reabsorbed by the lower edge of the pairing continuum. At intermediate temperatures between 0 and Tc we unify the newly found collective phenomena near Tc with the phononic and pair-breaking branches predicted from previous studies, and we exhaustively classify the roots of the analytically continued dispersion equation, and show that they provided a very good summary of the pair spectral functions.

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  • Received 16 November 2020
  • Accepted 7 April 2021

DOI:https://doi.org/10.1103/PhysRevA.103.043336

©2021 American Physical Society

Physics Subject Headings (PhySH)

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

S. N. Klimin1, J. Tempere1,2, and H. Kurkjian1,3

  • 1TQC, Universiteit Antwerpen, Universiteitsplein 1, B-2610 Antwerpen, Belgium
  • 2Lyman Laboratory of Physics, Harvard University, Cambridge, Massachusetts 02138, USA
  • 3Laboratoire de Physique Théorique, Université de Toulouse, CNRS, UPS, France

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Issue

Vol. 103, Iss. 4 — April 2021

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