Quasi-particle Lifetime in a Mixture of Bose and Fermi Superfluids

TL;DR

This paper investigates how quasi-particle interactions affect the lifetime of Bose superfluid quasi-particles in a Bose-Fermi mixture, revealing different damping behaviors on the BCS and BEC sides of the Fermi superfluid.

Contribution

It provides a theoretical analysis of quasi-particle damping rates in Bose-Fermi superfluids, highlighting the contrasting threshold behaviors on the BCS and BEC sides.

Findings

Damping rate is constant near the threshold in the BCS side.

Damping rate increases rapidly in the BEC side.

Results relate to collective mode experiments in Bose-Fermi mixtures.

Abstract

In this letter, to reveal the effect of quasi-particle interactions in a Bose-Fermi superfluid mixture, we consider the lifetime of quasi-particle of Bose superfluid due to its interaction with quasi-particles in Fermi superfluid. We find that this damping rate, i.e. inverse of the lifetime, has quite different threshold behavior at the BCS and the BEC side of the Fermi superfluid. The damping rate is a constant nearby the threshold momentum in the BCS side, while it increases rapidly in the BEC side. This is because in the BCS side the decay processe is restricted by constant density-of-state of fermion quasi-particle nearby Fermi surface, while such a restriction does not exist in the BEC side where the damping process is dominated by bosonic quasi-particles of Fermi superfluid. Our results are related to collective mode experiment in recently realized Bose-Fermi superfluid mixture.