Berezinskii-Kosterlitz-Thouless Phase Transition in 2D Spin-Orbit Coupled Fulde-Ferrell Superfluids

TL;DR

This paper investigates the Berezinskii-Kosterlitz-Thouless transition in 2D spin-orbit coupled Fulde-Ferrell superfluids, showing that finite temperature superfluidity is achievable with high transition temperatures, enabling experimental observation of topological phases.

Contribution

It demonstrates large BKT transition temperatures in 2D FF superfluids with spin-orbit coupling, facilitating their experimental realization at finite temperatures.

Findings

Large BKT transition temperature due to high superfluid densities

Stability of gapless FF superfluids from positive superfluid densities

Potential for observing topological excitations like Majorana fermions

Abstract

The experimental observation of traditional Zeeman-field induced Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) superfluids has been hindered by various challenges, in particular, the requirement of low dimensional systems. In 2D, finite temperature phase fluctuations lead to extremely small Berezinskii-Kosterlitz-Thouless (BKT) transition temperature for FFLO superfluids, raising serious concerns regarding their experimental observability. Recently, it was shown that FFLO superfluids can be realized using a Rashba spin-orbit coupled Fermi gas subject to Zeeman fields, which may also support topological excitations such as Majorana fermions in 2D. Here we address the finite temperature BKT transition issue in this system, which may exhibit gapped, gapless, topological, and gapless topological FF phases. We find a large BKT transition temperature due to large effective superfluid densities, making it possible to observe 2D FF superfluids at finite temperature. In addition, we show that gapless FF superfluids can be stable due to their positive superfluid densities. These findings pave the way for the experimental observation of 2D gapped and gapless FF superfluids and their associated topological excitations at finite temperature.