Pseudogap in Fermionic Density of States in the BCS-BEC Crossover of Atomic Fermi Gases

摘要

We study pseudogap behaviors of ultracold Fermi gases in the BCS-BEC crossover region. We calculate the density of states (DOS), as well as the single-particle spectral weight, above the superfluid transition temperature T_(c) including pairing fluctuations within a T-matrix approximation. We find that DOS exhibits a pseudogap structure in the BCS-BEC crossover region, which is most remarkable near the unitarity limit. We determine the pseudogap temperature T~(*) at which the pseudogap structure in DOS disappears. We also introduce another temperature T~(**) at which the BCS-like double-peak structure disappears in the spectral weight. While one finds T~(*) > T~(**) in the BCS regime, T~(**) becomes higher than T~(*) in the crossover and BEC regime. We also determine the pseudogap region in the phase diagram in terms of temperature and pairing interaction.