OPTICAL CONDUCTIVITY OF THE HUBBARD-MODEL IN THE STRONG-COUPLING REGIME

On the basis of a diagrammatic technique for Hubbard operators we calculate the real part of the frequency-dependent conductivity in the Hubbard model on any-dimensional cubic lattice at finite temperatures. Results in the lowest non-vanishing order of the perturbation theory are presented for various values of the parameters U, t and band fillings. We explicitly check the sum rule within the perturbation order. The 1/T behavior of the Drude weight is observed for temperatures t much less than k T much less than U.