Effects of nonmagnetic impurities on BCS-BEC crossover in atomic Fermi gases

We present a systematic investigation of the effects of nonmagnetic impurities on the $s$-wave BCS-BEC crossover within a pairing fluctuation theory. Both the pairing $T$-matrix and the impurity scattering $T$-matrix are treated self-consistently at the same time, in the context of ultracold atomic Fermi gases. While the system is less sensitive to impurity scattering in the Born limit, in the strong impurity scattering limit, both the frequency and the gap function are highly renormalized, leading to significant suppression of the superfluid $T_c$. In the BCS regime, the superfluidity may be readily destroyed by the impurity, leading to an effective power law dependence of $T_c$ as a function of pairing strength. In comparison, $T_c$ and (pseudo)gaps in the unitary and BEC regimes are relatively more robust. In either cases, the $s$-wave pairing is less sensitive to impurity than its $d$-wave counterpart. Calculations of superfluid density will also be presented. References: Q.J. Chen and J.R. Schrieffer, Phys. Rev. B 66, 014512 (2002).