Metastability in spin polarised Fermi gases and quasiparticle decays

TL;DR

This paper explores the metastability and decay processes of quasiparticles in spin-polarized Fermi gases, linking microscopic decay mechanisms to macroscopic phase stability, and proposes experimental probes for these phenomena.

Contribution

It introduces a detailed analysis of quasiparticle decay thresholds and rates, connecting them to the metastability of polarized phases in Fermi gases, and suggests experimental methods to observe these effects.

Findings

Identified decay processes and their thresholds for quasiparticles.

Linked quasiparticle stability to the metastability of the normal phase.

Predicted a metastable region for polarons in polarized Fermi gases.

Abstract

We investigate the metastability associated with the first order transition from normal to superfluid phases in the phase diagram of two-component polarised Fermi gases.We begin by detailing the dominant decay processes of single quasiparticles.Having determined the momentum thresholds of each process and calculated their rates, we apply this understanding to a Fermi sea of polarons by linking its metastability to the stability of individual polarons, and predicting a region of metastability for the normal partially polarised phase. In the limit of a single impurity, this region extends from the interaction strength at which a polarised phase of molecules becomes the groundstate, to the one at which the single quasiparticle groundstate changes character from polaronic to molecular. Our argument in terms of a Fermi sea of polarons naturally suggests their use as an experimental probe. We propose experiments to observe the threshold of the predicted region of metastability, the interaction strength at which the quasiparticle groundstate changes character, and the decay rate of polarons.