INCIPIENT ANTIFERROMAGNETISM AND LOW-ENERGY EXCITATIONS IN THE HALF-FILLED 2-DIMENSIONAL HUBBARD-MODEL

We present single-particle and thermodynamic properties of the half-fi lled single-band Hubbard model in 2D calculated in the self-consistent fluctuation exchange approximation. The low-energy excitations at mod erate temperatures and small U are quasiparticles with a short lifetim e. As the temperature is lowered, coupling to evolving spin fluctuatio ns leads to the extinction of these quasiparticles, signaled by a weak pseudogap in the density of states and by a positive slope in Re Sigm a(k(F), epsilon) and a local maximum in \Im Sigma(k(F), epsilon)\ at e psilon = 0. We explain these results using a simple spin-fluctuation m odel.