Transport Properties of Doped t-J Ladders

The conductivity and Hall coefficient for various types of t-J ladders are calculated as a function of temperature and frequency by numerical diagonalization. A crossover from incoherent to coherent charge dynamics is found at a temperature T_coh. There exists another crossover at T_PG below which a pseudogap opens in the optical spectra, induced by the opening of a spin gap. In the absence of the spin gap, T_coh and the coherent weight are suppressed especially with increasing dimensionality. On the contrary, T_coh is strongly enhanced by the pseudogap formation below T_PG, whereas the coherent Drude weight decreases with increasing dimensionality. The Hall coefficient shows a strong crossover at T_PG below which it has large amplitude for small doping concentration.