Pseudogap in the normal state of superfluid condensate formed by ultracold Fermi gases with particle–hole fluctuation

In the normal state of a superfluid condensate, like the Bardeen–Cooper–Schrieffer (BCS) superconducting state, we do not expect a gapped feature in the single-particle spectral function. Here we calculate the spectral function and single-particle density of states (DOS) of ultracold Fermi gases at different temperatures in the normal state. The calculation is conducted based on the non-self-consistent T-matrix approximation (nTMA) with particle–hole fluctuation. It is found that a dip structure emerges in the DOS above the superfluid phase-transition temperature T_c. We attribute this dip structure to the pseudogap, and its temperature is determined. From the temperature dependence of the spectral function, we also find another characteristic temperature where a two-peak structure disappears. The results provide deep insight into the superfluid condensate formed by ultracold fermions.