Constant E-J relation in the current induced resistive state of YBa2Cu3O7-x

Restoration of a resistive state between 4.3 K and T_c was investigated by exceeding the J_c of bulk YBa₂Cu₃O_7-x. Unlike the case of 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. This value was constant for a given sample between 4.3 K 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 4.2 K and T_c under applied magnetic fields up to 200 G. Two breaks in the E-J behavior were observed near T_c which are believed to correspond to the intergranular and intragranular J_cs, 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