Feasibility of a Fulde-Ferrell-Larkin-Ovchinnikov superfluid Fermi atomic gas

TL;DR

This paper proposes that optical lattice-induced Fermi surface anisotropy can stabilize the elusive FFLO superfluid phase in spin-imbalanced ultracold Fermi gases, overcoming fluctuation and phase separation challenges.

Contribution

It demonstrates that Fermi surface anisotropy in optical lattices stabilizes the FFLO state against pairing fluctuations and phase separation, advancing the pursuit of unconventional superfluids in cold atom systems.

Findings

Fermi surface anisotropy enhances FFLO stability.

FFLO state can overcome phase separation.

Stability achieved within strong-coupling theory.

Abstract

We theoretically explore a promising route to achieve the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state in a spin-imbalanced ultracold Fermi gas. In the current stage of cold atom physics, search for this exotic Fermi superfluid is facing two serious difficulties: One is the desperate destruction of the FFLO long-range order by FFLO pairing fluctuations, which precludes entering the phase through a second-order transition, even in three dimension. The other is the fierce competition with the phase separation into the BCS (Bardeen-Cooper-Schrieffer) state and the spin-polarized normal state. Including strong FFLO pairing fluctuations within the framework of the strong-coupling theory developed by Nozi\`eres and Schmitt-Rink, we show that the anisotropy of Fermi surface introduced by an optical lattice makes the FFLO state stable against the paring fluctuations. This stabilized FFLO state is also found to be able to overcome the competition with the phase separation under a certain condition. Since the realization of unconventional Fermi superfluids is one of the most exciting challenges in cold atom physics, our results would contribute to the further development of this field.