TEMPERATURE-DEPENDENCE OF THE JOSEPHSON CRITICAL-CURRENT IN BI2SR2CACU2O8+X BREAK JUNCTIONS

We measured the I-V characteristics of break junctions obtained at 4.2 K in single crystals of Bi2Sr2CaCu2O8+x that exhibited a stable nonhy steretic Josephson effect. The product I(c)R(N) at 4.2 K was about 10 mV and the I-V curves followed the Resistively Shunted Junction (RSJ) model up to the T-c of the crystals. The temperature dependence of the critical current I-c(T) is fitted by a new model that takes into acco unt the effect of an intrinsically depressed order parameter at the su rface of a superconductor with a short coherence length and, for compa rison, by a model that introduces the effect of a proximity layer and of a finite transparency at the junction interfaces. The results can i ndicate that the intrinsic lowering of the pair potential at the sampl e surfaces is the cause of the deviations of our I(c)R(N) from ideal B CS value.