Dynamical Mean Field Theory for the Normal Phase of the Attractive Hubbard Model

We analyze the normal phase of the attractive Hubbard model within dynamical mean field theory. We present results for the pair density, the spinsusceptibility, the specific heat, the momentum distribution, and for the quasiparticle weight. At weak coupling the low temperature behavior of all quantities is consistent with Fermi liquid theory. At strong coupling all electrons are bound in pairs, which leads to a spin gap and removes fermionic quasiparticle excitations. The transition between the Fermi liquid phase and the pair phase takes place at a critical coupling of the order of the band width and is generally discontinuous at sufficiently low temperature.