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 spin-susceptibility, the specific heat, the momentum distribution, and for the quasi-particle 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 quasi-particle 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.