ELECTRIC-FIELD-DEPENDENT VARIABLE-RANGE-HOPPING CONDUCTION IN PRBA2CU3O7-Y

The variable-range hopping conductivities of quasi-two-dimensional sys tems in electric fields were calculated for the cases of both constant and energy-dependent densities of states. The localized states were c onsidered to be randomly distributed in space and energy coordinates, and the carriers were considered to be distributed according to the Fe rmi distribution. Approximations yielded analytic results valid for mo st temperatures and electric fields and included localized states both above and below the Fermi level. We hypothesized that the localized s tates of PrBa2Cu3O7-y (PBCO) are distributed in the CuO planes, making that compound behave as a quasi-two-dimensional material. We compared our theory with experiments of PBCO-based junctions and found good ag reement between theory and experiment.