CONSTANT E-J RELATION IN THE CURRENT INDUCED RESISTIVE STATE OF YBA2CU3O7-X

Restoration of a resistive state between 4.3K and T(c) was investigated by exceeding J(c) of bulk YBa2Cu3O7-x. Unlike the low T(c) Type-II superconductors, where restoration of the normal state resistivity is obtained by exceeding J(c) by a fraction of J(c), a constant value of differential resistivity which was several to many times smaller than that of the normal state value was obtained. This constant E-J slope remained constant up to ten times the transport J(c). Even more surprisingly, this value was constant for a given sample between 4.3K and T(c). The normal state resistivity just above T(c) and the constant differential resistivity value below T(c) were different for each sample. Since the value of this slope did not change by temperature at ambient fields, the constant slope of the E-J curves is not due to field induced flux flow but may be due to a peculiar inhomogeneity of J(c) throughout the sample. This point is further proven by the constancy of this slope at temperatures between 4.2K and T(c) under applied magnetic fields up to 200 Gauss. Near T(c) we observed two breaks in the E-J behavior which we believe correspond to the inter and intragranular J(c)'s with the high J(c) in agreement with reported values obtained by magnetization. Microstructural results imply that the mechanism for the observed behavior may be weak link related.