Nature of superfluidity in ultracold Fermi gases near Feshbach resonances

We study the superfluid state of atomic Fermi gases using a BCS-Bose-Einstein-condensation crossover theory. Our approach emphasizes noncondensed fermion pairs which strongly hybridize with their (Feshbach-induced) molecular boson counterparts. These pairs lead to pseudogap effects above $T_c$ and non-BCS characteristics below. We discuss how these effects influence the experimental signatures of superfluidity.

Figure 1

$T_c$ vs detuning ${\nu }_0$. The upper inset plots the pseudogap at $T_c$ vs ${\nu }_0$, and the lower inset plots molecular boson contribution to the condensate weight and fermionic chemical potential at $T=0$.

Figure 2

Fermionic momentum distribution function at $T=0$ and $T=T_c$ for the three regimes. PG corresponds to maximal $T_c$. The inset plots the $T$ dependent excitation gap below $T_c$.

Figure 3

Fermionic density of states vs energy for the three regimes at three indicated temperatures. Note the difference in the scales.