Flow and critical velocity of an imbalanced Fermi gas through an optical potential

TL;DR

This paper investigates how population imbalance affects the flow and critical velocity of a Fermi superfluid in an optical lattice, revealing a monotonic decrease of critical velocity to zero with increasing imbalance.

Contribution

It provides analytical expressions for the tunneling contribution and critical velocity in an imbalanced Fermi superfluid within an optical lattice.

Findings

Critical velocity decreases monotonically with imbalance.

Analytical formulas relate critical velocity to pairing energy and imbalance.

Flow is analyzed considering second-order interlayer tunneling.

Abstract

Optical lattices offer the possibility to investigate the superfluid properties of both Bose condensates and Fermionic superfluid gases. When a population imbalance is present in a Fermi mixture, this leads to frustration of the pairing, and the superfluid properties will be affected. In this contribution, the influence of imbalance on the flow of a Fermi superfluid through an optical lattice is investigated. The flow through the lattice is analysed by taking into account coupling between neighbouring layers of the optical lattice up to second order in the interlayer tunneling amplitude for single atoms. The critical velocity of flow through the lattice is shown to decrease monotonically to zero as the imbalance is increased to 100%. Closed-form analytical expressions are given for the tunneling contribution to the action and for the critical velocity as a function of the binding energy of pairs in the (quasi) two-dimensional Fermi superfluid and as a function of the imbalance.