Decay of polarons and molecules in a strongly polarized Fermi gas

TL;DR

This paper investigates the transition between polaron and molecule states in a polarized Fermi gas, revealing suppressed coupling, confirming a first-order transition, and showing long-lived quasiparticles with potential for experimental observation.

Contribution

It demonstrates that the coupling between polaron and molecule states is strongly suppressed, confirming the first-order nature of their transition and revealing long-lived quasiparticles.

Findings

Coupling between polaron and molecule states is strongly suppressed.

The transition is confirmed to be first order.

Quasiparticle lifetimes are much longer than in typical Fermi liquids.

Abstract

The ground state of an impurity immersed in a Fermi sea changes from a polaron to a molecule as the interaction strength is increased. We show here that the coupling between these two states is strongly suppressed due to a combination of phase space effects and Fermi statistics, and that it vanishes much faster than the energy difference between the two states, thereby confirming the first order nature of the polaron-molecule transition. In the regime where each state is metastable, we find quasiparticle lifetimes which are much longer than what is expected for a usual Fermi liquid. Our analysis indicates that the decay rates are sufficiently slow to be experimentally observable.