Pair fluctuation induced pseudogap in the normal phase of the   two-dimensional attractive Hubbard model at weak coupling
  One-particle spectral properties in the normal phase of the two-dimensional attractive Hubbard model are investigated in the weak coupling regime using the non-selfconsistent T-matrix approximation. The corresponding equations are evaluated numerically directly on the real frequency axis. For temperatures sufficiently close to the superconducting transition temperature a pseudogap in the one-particle spectral function is observed, which can be assigned to the increasing importance of pair fluctuations. 
Daniel Rohe and Walter Metzner