Inhomogeneous Pseudogap Phenomenon in the BCS-BEC Crossover Regime of a Trapped Superfluid Fermi Gas

Abstract

We investigate pseudogap phenomena in the unitarity limit of a trapped superfluid Fermi gas. Including effect of strong pairing fluctuations within a $T$-matrix approximation, as well as effects of a harmonic trap within the local density approximation (LDA), we calculate the local superfluid density of states below the superfluid phase transition temperature $T_{\rm c}$. We show that the spatial region where single-particle excitations are dominated by the pseudogap may still exist even below $T_{\rm c}$, due to inhomogeneous pairing fluctuations caused by the trap potential. From the temperature dependence of the pseudogapped density of states, we identify the pseudogap regime of the unitarity Fermi gas with respect to the temperature and spatial position. We also show that the combined $T$-matrix theory with the LDA can quantitatively explain the local pressure which was recently observed in the unitarity limit of a $^6$Li Fermi gas.