Beyond mean-field corrections to the quasiparticle spectrum of superfluid Fermi gases

TL;DR

This paper analyzes how beyond mean-field effects influence the quasiparticle spectrum in superfluid Fermi gases, providing detailed calculations of lifetime, energy shifts, and corrections to key physical quantities.

Contribution

It introduces a detailed calculation of quasiparticle lifetime and energy shifts due to collective mode coupling in the BCS-BEC crossover, extending beyond mean-field theory.

Findings

Quasiparticles remain undamped near the spectrum minimum.

Corrections to the energy gap and effective mass are quantified.

Results are relevant for interpreting experimental measurements.

Abstract

We investigate the fermionic quasiparticle branch of superfluid Fermi gases in the BCS-BEC crossover and calculate the quasiparticle lifetime and energy shift due to its coupling with the collective mode. The only close-to-resonance process that low-energy quasiparticles can undergo at zero temperature is the emission of a bosonic excitation from the phononic branch. Close to the minimum of the branch we find that the quasiparticles remain undamped, allowing us to compute corrections to experimentally relevant quantities such as the energy gap, location of the minimum, effective mass, and Landau critical velocity.