Incipient antiferromagnetism and low-energy excitations in the half-filled two-dimensional hubbard model

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