Interacting Preformed Cooper Pairs in Resonant Fermi Gases

TL;DR

This paper investigates the interactions between preformed Cooper pairs in a strongly interacting Fermi gas using a Wilsonian renormalization-group approach, improving upon the noninteracting pair approximation and aligning well with recent experimental results.

Contribution

It introduces a Wilsonian renormalization-group scheme to account for interactions between Cooper pairs, extending the Nozi extquotesingle{}res-Schmitt-Rink theory.

Findings

Good agreement with recent experimental data

Predictions for population-imbalanced Fermi gases

Enhanced understanding of pair interactions in strongly correlated systems

Abstract

We consider the normal phase of a strongly interacting Fermi gas, which can have either an equal or an unequal number of atoms in its two accessible spin states. Due to the unitarity-limited attractive interaction between particles with different spin, noncondensed Cooper pairs are formed. The starting point in treating preformed pairs is the Nozi\`{e}res-Schmitt-Rink (NSR) theory, which approximates the pairs as being noninteracting. Here, we consider the effects of the interactions between the Cooper pairs in a Wilsonian renormalization-group scheme. Starting from the exact bosonic action for the pairs, we calculate the Cooper-pair self-energy by combining the NSR formalism with the Wilsonian approach. We compare our findings with the recent experiments by Harikoshi {\it et al.} [Science {\bf 327}, 442 (2010)] and Nascimb\`{e}ne {\it et al.} [Nature {\bf 463}, 1057 (2010)], and find very good agreement. We also make predictions for the population-imbalanced case, that can be tested in experiments.