Cooperative weak links in sintered Y-Ba-Cu-O superconductor

The I-V characteristics of Y-Ba-Cu-O have been measured for several temperatures below $T_c$. A clear ‘‘footlike’’ structure is developed when the temperature goes down from $T_c$, strongly reminiscent of the case in superconducting weak links. The energy gap derived from the critical current and the ‘‘excess current’’ is about 18.4 meV at T=0 and with a roughly Bardeen-Cooper-Schrieffer-type of variation at T>0. The results are indicative of a kind of ‘‘cooperative’’ weak link behavior in sintered superconducting Y-Ba-Cu-O.