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Pair-breaking collective branch in BCS superconductors and superfluid Fermi gases

Journal Contribution - e-publication

We demonstrate the existence of a collective excitation branch in the pair-breaking continuum of superfluid Fermi gases and BCS superconductors. At zero temperature, we analytically continue the equation on the collective mode energy in Anderson's Random Phase Approximation or Gaussian fluctuations through its branch cut associated with the continuum, and obtain the full complex dispersion relation, including in the strong coupling regime. The branch exists as long as the chemical potential mu is positive and the wave number below root 2m mu/(h) over bar (with m the fermion mass). In the long wavelength limit, the branch varies quadratically with the wave number, with a complex effective mass that we compute analytically for an arbitrary interaction strength.
Journal: Physical review letters
ISSN: 0031-9007
Volume: 122
Publication year:2019
Keywords:A1 Journal article
BOF-keylabel:yes
BOF-publication weight:6
CSS-citation score:2
Authors:International
Authors from:Higher Education
Accessibility:Open