VARIABLE-RANGE-HOPPING AND POSITIVE MAGNETORESISTANCE IN INSULATING Y1-XPRXBA2CU3O7 CRYSTALS

We have measured in-plane resistivity and magnetoresistance of insulating Y1-xPrxBa2Cu3O7 (x approximately 0.63) crystals in magnetic fields up to 8 T. Mott variable-range-hopping transport rho=rho0 exp{(T0/T)alpha} has been observed with alpha=1/4 at low temperatures suggesting the metal-insulator transition caused by Pr doping is due to carrier localization. The magnetoresistance in the Mott variable-range-hopping regime is found to be positive and anisotropic, which may be caused by a decrease of the localiztion length induced by the magnetic field.