Stabilising Fulde-Ferrel-Larkin-Ovchinnikov Superfluidity with long-range Interactions in a mixed dimensional Bose-Fermi System

TL;DR

This paper investigates how long-range interactions mediated by a Bose-Einstein condensate can stabilize inhomogeneous superfluid phases in a layered fermionic system, revealing a large tunable parameter space for such phases.

Contribution

It introduces a system with tunable long-range interactions in a mixed dimensional Bose-Fermi setup, demonstrating enhanced stability of inhomogeneous superfluid phases compared to short-range systems.

Findings

Large inhomogeneous superfluid region identified in phase diagrams.

Range of interaction controlled by BEC healing length enhances superfluid stability.

Superfluid phases meet at a tricritical point, with suppressed critical temperature in inhomogeneous phases.

Abstract

We analyse the stability of inhomogeneous superfluid phases in a system consisting of identical fermions confined in two layers that are immersed in a Bose-Einstein condensate (BEC). The fermions in the two layers interact via an induced interaction mediated by the BEC, which gives rise to pairing. We present zero temperature phase diagrams varying the chemical potential difference between the two layers and the range of the induced interaction, and show that there is a large region where an inhomogeneous superfluid phase is the ground state. This region grows with increasing range of the induced interaction and it can be much larger than for a corresponding system with a short range interaction. The range of the interaction is controlled by the healing length of the BEC, which makes the present system a powerful tunable platform to stabilise inhomogeneous superfluid phases. We furthermore analyse the melting of the superfluid phases in the layers via phase fluctuations as described by the Berezinskii-Kosterlitz-Thouless mechanism and show that the normal, homogeneous and inhomogeneous superfluid phases meet in a tricritical point. The superfluid density of the inhomogeneous superfluid phase is reduced by inherent gapless excitations, and we demonstrate that this leads to a significant suppression of the critical temperature as compared to the homogeneous superfluid phase.