CHARGE DYNAMICS IN THE PLANAR T-J MODEL

The finite-temperature optical conductivity sigma(omega) in the planar t-J model is analyzed using recently introduced numerical method ba;sed on the Lanczos diagonalisation of small systems (up to 20 sites), as well as by analytical approaches, including the method of frequency moments and the retraceable-path approximation. Results for a dynamical mobility of a single hole at elevated temperatures T > t reveal a Gaussian-like mu(omega) spectra, however, with a nonanalytical behavior at low omega. In the single-hole response a difference between the ferromagnetic (J = 0) and the antiferromagnetic (J > 0) polaron shows up at T < J. At larger dopings numerical results in studied systems are consistent with the thermodynamical behavior for T > T* greater than or equal to 0.1t. sigma(omega) spectra show a non-Drude falloff at large frequencies. In particular for ''optimum'' doping n(h) similar to 0.2 we obtain in the low-omega, T regime the relaxation rate r(-1) similar to 2 pi lambda(omega + xi T) with lambda similar to 0.09 and xi similar to 2.7, being consistent with the marginal Fermi-liquid concept and experiments. Within the same regime we reproduce the nearly linear variation of de resistivity rho with T. This behavior is weakly dependent on J, provided that J < t.