Fulde-Ferrell Superfluids without Spin Imbalance in Driven Optical Lattices

TL;DR

This paper proposes a novel method to realize Fulde-Ferrell superfluids in cold atom optical lattices without requiring spin imbalance, by coupling orbital bands to create a spin-independent Fermi surface mismatch.

Contribution

It introduces a new scheme to achieve FF superfluidity without spin imbalance using orbital band coupling in optical lattices.

Findings

Proposes a spin-independent Fermi surface mismatch mechanism.

Demonstrates a route to realize FF superfluids without Zeeman fields.

Provides theoretical framework for experimental realization.

Abstract

Spin-imbalanced ultracold Fermi gases have been widely studied recently as a platform for exploring the long-sought Fulde-Ferrell-Larkin-Ovchinnikov superfluid phases, but so far conclusive evidence has not been found. Here we propose to realize an Fulde-Ferrell (FF) superfluid without spin imbalance in a three-dimensional fermionic cold atom optical lattice, where $s$- and $p$-orbital bands of the lattice are coupled by another weak moving optical lattice. Such coupling leads to a spin-independent asymmetric Fermi surface, which, together with the $s$-wave scattering interaction between two spins, yields an FF type of superfluid pairing. Unlike traditional schemes, our proposal does not rely on the spin imbalance (or an equivalent Zeeman field) to induce the Fermi surface mismatch and provides a completely new route for realizing FF superfluids.