Pseudogap behaviors of atomic Fermi gases above T_c in the BCS-BEC crossover

We investigate pseudogap behaviors of an ultracold Fermi gas in the BCS-BEC crossover above the superfluid transition temperature Tc. We calculate the single-particle density of states (DOS), as well as the spectral weight, over the entire BCS-BEC crossover region, including strong pairing fluctuations within a T-matrix approximation. We show that the pseudogap structure in DOS develops from the weak-coupling BCS region, and continuously changes into a fully gapped one in the strong-coupling BEC region. We determine the pseudogap temperature T at which the dip structure in DOS disappears, and identify the pseudogap region in the phase diagram in terms of temperatures and pairing interactions.