Pair-Breaking Collective Branch in BCS Superconductors and Superfluid Fermi Gases

Abstract

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 $\sqrt{2m\mu }/\hslash$ (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.

6-7 pages, 4 figures, in English et en français

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• Geometric contribution to the Goldstone mode in spin-orbit coupled Fermi superfluids
• Collective excitations of superfluid Fermi gases near the transition temperature
• Leggett collective excitations in a two-band Fermi superfluid at finite temperatures
• Exciting the Higgs mode in a strongly-interacting Fermi gas by interaction modulation
• Probing two Higgs oscillations in a one-dimensional Fermi superfluid with Raman-type spin-orbit coupling
• Beyond mean-field corrections to the quasiparticle spectrum of superfluid Fermi gases
• Dispersion of plasmons in three-dimensional superconductors
• Spatially-resolved dynamics of the amplitude Schmid-Higgs mode in disordered superconductors
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• Quantum Fluctuations and Multifractally-Enhanced Superconductivity in Disordered Thin Films
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• Hybrid-pair superfluidity in a strongly driven Fermi gas
• Linear response of a superfluid Fermi gas inside its pair-breaking continuum
• Quantum transport in strongly correlated Fermi gases
• Low-Lying Collective Excitations of Superconductors and Charged Superfluids
• Superfluid properties of an ultracold Fermi gas with an orbital Feshbach resonance in the BCS-BEC crossover region
• Bragg spectroscopy and pair-breaking-continuum mode in a superfluid Fermi gas
• Quasiparticle disintegration in fermionic superfluids
• BCS-BEC crossover in a quasi-two-dimensional Fermi superfluid
• Higgs oscillations in a unitary Fermi superfluid
• Small amplitude collective modes of a finite-size unitary Fermi gas in deformed traps
• Two-band atomic superfluidity in the presence of an orbital Feshbach resonance
• Hybrid collective excitations in topological superconductor/ferromagnetic insulator heterostructures