Optical conductivity of the Hubbard model at finite temperature.

The optical conductivity, σ(ω), of the two dimensional one-band Hubbard model is calculated at finite temperature using exact diagonalization techniques on finite clusters. The in-plane d.c. resistivity, ρab, is also evaluated. We find that at large U/t and temperature T, ρab is approximately linear with temperature, in reasonable agreement with experiments on high-Tc superconductors. Moreover, we note that σ(ω) displays charge excitations, a mid-infrared (MIR) band and a Drude peak, also as observed experimentally. The combination of the Drude peak and the MIR oscillator strengths leads to a conductivity that decays slower than 1/ω at energies smaller than the insulator gap near half-filling.