Bound State of Ultracold Fermions in the Spin Imbalanced Normal State

TL;DR

This paper investigates how Fano-Feshbach resonances induce long-lived bosonic modes in a polarized Fermi gas, revealing a first order quantum phase transition and unconventional pairing phenomena.

Contribution

It demonstrates the formation of bifermions and biholes in a polarized Fermi gas due to FF resonances, highlighting their role as signatures of a quantum phase transition.

Findings

Fano-Feshbach resonances lead to long-lived bosonic modes in polarized Fermi gases.

These modes appear in the weak coupling limit, indicating unconventional pairing.

The results support the possibility of fermionic pairing effects in the normal state with population imbalance.

Abstract

We study a polarized Fermi gas and demonstrate that Fano-Feshbach (FF) resonances lead to the pairing of fermions and holes into long living massive bosonic modes (bifermions and biholes), which can be viewed as signatures of a first order quantum phase transition. These modes, which are neither conventional Cooper pairs nor closed channel bosonic dimers, have a peculiar dispersion relation and appear already in the weak coupling limit, i.e. for large FF detunings. Our result is in accord with claims of Schunck \emph{et al.} [cond-mat/0702066] that by stabilizing the normal state the population imbalance still allows effect of s-wave fermionic pairing.