Shift of the molecular bound state threshold in dense ultracold Fermi gases with Feshbach resonance

TL;DR

This paper studies how the presence of a Fermi sea in dense ultracold Fermi gases shifts the bound state formation threshold near a Feshbach resonance, aligning with recent experimental results.

Contribution

It demonstrates that Pauli exclusion causes a significant shift in the bound state threshold in dense Fermi gases, extending understanding of many-body effects near Feshbach resonances.

Findings

Large shift of the threshold due to Fermi sea effects

Shift magnitude is comparable to the Feshbach resonance width

Agreement with recent experimental observations

Abstract

We consider a dense ultracold Fermi gas in the presence of a Feshbach resonance. We investigate how the treshold for bound state formation, which is just at the Feshbach resonance for a dilute gas, is modified due to the presence of the Fermi sea. We make use of a preceding framework of handling this many-body problem. We restrict ourselves to the simple case where the chemical potential $ \mu $ is negative, which allows us to cover in particular the classical limit where the effect is seen to disappear. We show that, within a simple approach where basically only the effect of Pauli exclusion is included, the Fermi sea produces a large shift of the threshold, which is of order of the width of the Feshbach resonance. This is in agreement with very recent experimental findings.