SINGLE-PARTICLE SELF-ENERGY AND OPTICAL CONDUCTIVITY OF THE SIMPLIFIED HUBBARD-MODEL

It is shown that the single-particle self-energy of the one and two-di mensional simplified Hubbard model exhibits different behavior charact erized by Fermi-liquid, non-Fermi-liquid quasiparticle, or non-quasipa rticle excitations, as a function of the strength of the on-site Coulo mb repulsion U, temperature, and electron filling. For half-filled lat tices, results for the optical conductivity indicate that the d.c. con ductivity is zero for all temperatures and U>0.