OPTICAL CONDUCTIVITY IN THE T-J-MODEL

Frequency dependent conductivity sigma(omega) is calculated for the t - J model by applying the memory function technique in terms of the Hu bbard operators. The relaxation rate due to electron scattering on spi n and charge dynamical fluctuations is calculated and a generalized Dr ude law for sigma(omega) is obtained. For a model with an incoherent s pectrum for one-hole excitations we obtain a universal form for freque ncy dependence of relaxation rate and conductivity in terms of the sca ling function gamma(omega/kT). The relaxation rate for the t - J model is quite different from that one for the conventional Hubbard model i n the strong coupling limit where it vanishes due to an exact cancella tion of the intraband scattering and virtual interband transitions.