Optical conductivity of the two-dimensional Hubbard model

The optical conductivity σ₁({ω}) of the two-dimensional Hubbard model on finite clusters of 4×{}4 and {}10 ×{} {}10 sites is reported. Experimental features found in the high-Tc 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 σ₁({ω}), we need to work with a coupling constant of the order of the bandwidth, i.e., U/t{~}8--10. Results for the negative-U Hubbard model are included for comparison.