Nonlinear conduction in La_2-xBa_xCuO₄

We have investigated the electric-field dependence of the electrical conductivity in La_2-xBa_xCuO₄ with x = 0.03 and 0.125 (=1/8) where the superconductivity is suppressed. For x = 0.03, nonlinear conduction has been observed at low temperatures where the low-current resistivity increases with decreasing temperature. The observed nonlinearity can be well represented by the electric-field dependence of the conductivity in the Anderson-localized state. For x = 0.125, on the other hand, the conductivity is independent of the applied field within the measured field-range. We speculate that this result at x = 1/8 is due to the formation of static stripe-order of holes and spins, as discovered in La_1.6-xNd_0.4Sr_xCuO₄ with x = 1/8.