ANTIFERROMAGNETIC SPIN-FLUCTUATION EFFECTS ON QUASI-PARTICLE DAMPING AND SUPERCONDUCTIVITY IN HIGH-TC MATERIALS

First we calculate the random-phase-approximation (RPA) dynamic spin susceptibility of a two-dimensional (2D) Hubbard model for different band fillings and on-site Coulomb couplings U. The q-averaged spectral function for antiparamagnon exchange interaction starts linearly in frequency and then becomes almost constant, in agreement with "nested Fermi-liquid theory." Employing this interaction function we solve the Migdal-Eliashberg equations for the self-energy of quasiparticles in the 2D tight-binding band. In the normal state the damping rate of quasiparticles varies approximately linearly with frequency above omega-c and linearly in temperature above T*, where omega-c and T* increase with decreasing degrees of nesting of the Fermi surface (omega-c and T* denote the cross-over values from quadratic to linear behavior). For a realistic choice of parameters we find qualitative agreement with inverse particle lifetimes obtained from infrared-reflectivity and photoemission data in the high-T(c) materials. Within the RPA we find that the d-wave and extended s-wave pairing interactions due to exchange of one antiparamagnon is not strong enough to explain high-T(c) behavior.