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, ${\mathrm{\rho }}_{\mathit{a}\mathit{b}}$, is also evalauted. We find that at large U/t and temperature T, ${\mathrm{\rho }}_{\mathit{a}\mathit{b}}$ 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/${\mathrm{\omega }}^2$ at energies smaller than the insulator gap near half filling.