Impurity effects on BCS-BEC crossover in ultracold atomic Fermi gases

TL;DR

This paper systematically studies how nonmagnetic impurities affect the BCS-BEC crossover in ultracold Fermi gases, revealing impurity-induced suppression of superfluid properties and formation of impurity bands.

Contribution

It introduces a self-consistent pairing fluctuation theory to analyze impurity effects across the BCS-BEC crossover in atomic Fermi gases.

Findings

Strong impurities significantly suppress superfluid transition temperature and order parameter.

Impurity bands form and coherence peaks smear in the density of states.

Superfluidity is more robust in the unitary and BEC regimes than in the BCS regime.

Abstract

We present a systematic investigation of the effects of "nonmagnetic" impurities on the $s$-wave BCS-BEC crossover in atomic Fermi gases within a pairing fluctuation theory. Both pairing and impurity scattering $T$-matrices are treated self-consistently at the same time. While the system is less sensitive to impurity scattering in the Born limit, for strong impurity scatterers, both the frequency and the gap function are highly renormalized, leading to significant suppression of the superfluid $T_c$, the order parameter and the superfluid density. We also find the formation of impurity bands and smearing of coherence peak in the fermion density of states, leading to a spectrum weight transfer and finite lifetime of Bogoliubov quasiparticles. In the BCS regime, the superfluidity may be readily destroyed by the impurity of high density. In comparison, the superfluidity in unitary and BEC regimes is relatively more robust.