Damping of the Anderson-Bogolyubov mode by spin and mass imbalance in Fermi mixtures

TL;DR

This paper investigates how spin and mass imbalance in Fermi mixtures lead to damping of collective modes, deriving conditions for damping at zero temperature and comparing analytical and numerical results.

Contribution

It introduces a detailed analysis of damping mechanisms for Anderson-Bogolyubov modes in imbalanced Fermi mixtures, including conditions for damping at zero temperature.

Findings

Damping can occur at zero temperature with sufficient Fermi surface mismatch.

Analytical conditions for damping are derived and validated.

Numerical damping rates agree with analytical predictions.

Abstract

We study the temporally nonlocal contributions to the gradient expansion of the pair fluctuation propagator for spin- and mass-imbalanced Fermi mixtures. These terms are related to damping processes of sound-like (Anderson-Bogolyubov) collective modes and are relevant for the structure of the complex pole of the pair fluctuation propagator. We derive conditions under which damping occurs even at zero temperature for large enough mismatch of the Fermi surfaces. We compare our analytical results with numerically computed damping rates of the Anderson-Bogolyubov mode.