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 dc resistivity, ρab, is also evalauted. We find that at large U/t and temperature T, ρab is approximately linear with temperature. We also observed that {σ}({ω}) displays charge excitations, a midinfrared (MIR) band, and a Drude peak. The combination of the Drude peak and the MIR oscillator strengths leads to a conductivity that decays slower than 1/ω² at energies smaller than the insulator gap near half filling.