Collective modes of a soliton train in a Fermi superfluid

TL;DR

This paper investigates the collective excitations of a soliton train in a quasi-one-dimensional Fermi superfluid, revealing novel gapped modes, instabilities, and stabilization methods for long-lived FFLO states.

Contribution

It introduces a mean-field analysis of soliton train modes, identifying new gapped oscillation modes and proposing stabilization of FFLO phases through fermion filling.

Findings

Discovery of long-lived gapped modes associated with soliton oscillations

Identification of instability conditions depending on interaction strength and soliton spacing

Proposal to stabilize FFLO phases by filling solitons with unpaired fermions

Abstract

We characterize the collective modes of a soliton train in a quasi-one-dimensional Fermi superfluid, using a mean-field formalism. In addition to the expected Goldstone and Higgs modes, we find novel long-lived gapped modes associated with oscillations of the soliton cores. The soliton train has an instability that depends strongly on the interaction strength and the spacing of solitons. It can be stabilized by filling each soliton with an unpaired fermion, thus forming a commensurate Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phase. We find that such a state is always dynamically stable, which paves the way for realizing long-lived FFLO states in experiments via phase imprinting.