BEC-BCS crossover in an optical lattice

TL;DR

This paper develops a microscopic theory for the BEC-BCS crossover in an optical lattice, demonstrating that despite multiband effects near Feshbach resonances, a single-band model suffices for most cases.

Contribution

It introduces a criterion showing the BEC-BCS crossover can be effectively described by a single-band model away from the Feshbach resonance.

Findings

The Feshbach resonance induces multiband effects in the crossover.

A criterion for single-band applicability is proposed and validated.

Most known Feshbach resonances satisfy this criterion.

Abstract

We present the microscopic theory for the BEC-BCS crossover of an atomic Fermi gas in an optical lattice, showing that the Feshbach resonance underlying the crossover in principle induces strong multiband effects. Nevertheless, the BEC-BCS crossover itself can be described by a single-band model since it occurs at magnetic fields that are relatively far away from the Feshbach resonance. A criterion is proposed for the latter, which is obeyed by most known Feshbach resonances in ultracold atomic gases.