Abstract
Electrons at the van Hove point of a two-dimensional band model are studied in the weak-coupling limit as the condensation of the AF mode is approached from the paramagnetic phase. The interaction with fluctuations is treated in the one-loop approximation. It is found that for underdamped fluctuations the quasi-particle peak at the Fermi level is preserved down to the transition point, i.e. the van Hove singularity is not suppressed by the pseudogap, in contrast to what was found previously in the adiabatic approximation. However, the strength of the peak vanishes quadratically with the frequency of the AF mode when the latter is small.