Larkin-Ovchinnikov superfluidity in a two-dimensional imbalanced atomic Fermi gas

TL;DR

This paper investigates the properties and phase transitions of Larkin-Ovchinnikov superfluidity in a two-dimensional spin-imbalanced Fermi gas using mean-field theory, revealing a broader LO phase region and the nature of phase transitions.

Contribution

It provides a systematic mean-field analysis of 2D LO superfluidity, exploring phase diagrams and transition orders in both canonical and grand canonical ensembles.

Findings

Broader parameter space for 2D LO phase compared to 3D.

Weak first-order transition between LO and BCS phases.

Superfluid density decreases with increasing polarization.

Abstract

We present an extensive study of two-dimensional Larkin-Ovchinnikov (LO) superfluidity in a spin-imbalanced two-component atomic Fermi gas. In the context of Fulde-Ferrell-Larkin- Ovchinnikov (FFLO) phase, we explore a wide and generic class of pairing gap functions with ex- plicit spatial dependency. The mean-field theory of such phases is applied through the Bogoliubov-de Gennes equations in which the pairing gap can be determined self-consistently. In order to systemat- ically explore the configuration space we consider both the canonical and grand canonical ensembles where we control the polarization or chemical potentials of the system, respectively. The mean-field calculations enable us to understand the nature of the phase transitions in the fully paired Bardeen- Cooper-Schrieffer (BCS) state, exotic LO phase, and partially polarized free Fermi gas. The order of the phase transitions has been examined and in particular we find a weak first-order phase transition between the exotic inhomogeneous LO phase and the BCS phase. In comparison to the three-dimensional case, where the phase diagram is dominated by a generic separation phase, we predict a broader parameter space for the spatially inhomogeneous LO phase. By computing the superfluid density of the LO phase at different polarization, we show how the superfluidity of the system is suppressed with increasing spin polarization.