Constant E-J relation in the current induced resistive state of YBa/sub 2/Cu/sub 3/O/sub 7-x/

Restoration of a resistive state between 4.3 K and T/sub c/ was investigated by exceeding the J/sub c/ of bulk YBa/sub 2/Cu/sub 3/O/sub 7-x/. Unlike the case of low-T/sub c/ Type-II superconductors, where restoration of the normal state resistivity is obtained by exceeding J/sub c/ by a fraction of J/sub 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/sub c/. This value was constant for a given sample between 4.3 K and T/sub c/. The normal state resistivity just above T/sub c/ and the constant differential resistivity value below T/sub 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/sub c/ throughout the sample. This point is further proven by the constancy of this slope at temperatures between 4.2 K and T/sub c/ under applied magnetic fields up to 200 G. Two breaks in the E-J behavior were observed near T/sub c/ which are believed to correspond to the intergranular and intragranular J/sub c/s, with the high J/sub c/ in agreement with reported values obtained by magnetization. Microstructural results imply that the mechanism for the observed behavior may be weak-link-related.