A strongly interacting Sarma superfluid near orbital Feshbach resonances

TL;DR

This paper explores the properties of a strongly interacting Sarma superfluid in a three-dimensional Fermi gas near orbital Feshbach resonances, highlighting its stability, collective modes, and experimental prospects.

Contribution

It demonstrates the stability of a Sarma superfluid with gapless excitations in a two-channel model and analyzes its collective modes and experimental signatures.

Findings

Sarma superfluid is favored at large imbalance in the closed channel.

The superfluid supports a Goldstone-Anderson-Bogoliubov phonon and a Leggett mode.

The Leggett mode disappears at high momentum, and the phonon mode becomes damped.

Abstract

We investigate the nature of superfluid pairing in a strongly interacting Fermi gas near orbital Feshbach resonances with spin-population imbalance in three dimensions, which can be well described by a two-band or two-channel model. We show that a Sarma superfluid with gapless single-particle excitations is favored in the closed channel at large imbalance. It is thermodynamically stable against the formation of an inhomogeneous Fulde\textendash Ferrell\textendash Larkin\textendash Ovchinnikov superfluid and features a well-defined Goldstone-Anderson-Bogoliubov phonon mode and a massive Leggett mode as collective excitations at low momentum. At large momentum, the Leggett mode disappears and the phonon mode becomes damped at zero temperature, due to the coupling to the particle-hole excitations. We discuss possible experimental observation of a strongly interacting Sarma superfluid with ultracold alkaline-earth-metal Fermi gases.