Finite temperature damping of collective modes of a BCS-BEC crossover superfluid

TL;DR

This paper introduces a new mechanism explaining the damping of collective modes in a superfluid Fermi gas, emphasizing phonon-quasiparticle interactions over pair-breaking, with results aligning well with experiments.

Contribution

It presents an effective field theory model that identifies phonon-quasiparticle interactions as the main damping mechanism in a BCS-BEC crossover superfluid.

Findings

Damping is mainly due to phonon-quasiparticle interactions.

Model results agree quantitatively with experimental data.

Provides a new perspective on superfluid excitation damping mechanisms.

Abstract

A new mechanism is proposed to explain the puzzling damping of collective excitations, which was recently observed in the experiments of strongly interacting Fermi gases below the superfluid critical temperature on the fermionic (BCS) side of Feshbach resonance. Sound velocity, superfluid density and damping rate are calculated with effective field theory. We find that a dominant damping process is due to the interaction between superfluid phonons and thermally excited fermionic quasiparticles, in contrast to the previously proposed pair-breaking mechanism. Results from our effective model are compared quantitatively with recent experimental findings, showing a good agreement.