OPTICAL CONDUCTIVITY OF THE 2-DIMENSIONAL HUBBARD-MODEL

The optical conductivity sigma(1)(omega) of the two-dimensional Hubbard model on finite clusters of 4 x 4 and square root 10 x square root 10 sites is reported. Experimental features found in the high-T(c) cuprate superconductors can be qualitatively reproduced by this model including the presence of mid-infrared spectral weight, a Drude peak whose intensity grows with doping and a total spectral weight that varies slowly as the system is doped away from half filling. We find that to reproduce qualitatively the main experimental features of sigma(1)(omega), we need to work with a coupling constant of the order of the bandwidth, i.e., U/t approximately 8-10. Results for the negative-U Hubbard model are included for comparison.