Temperature dependence of the Josephson critical current in Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8+x/ break junctions

We measured the I-V characteristics of break junctions obtained at 4.2 K in single crystals of Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8+x/ that exhibited a stable nonhysteretic Josephson effect. The product I/sub c/R/sub 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/sub c/ of the crystals. The temperature dependence of the critical current I/sub c/(T) is fitted by a new model that takes into account the effect of an intrinsically depressed order parameter at the surface of a superconductor with a short coherence length and, for comparison, by a model that introduces the effect of a proximity layer and of a finite transparency at the junction interfaces. The results can indicate that the intrinsic lowering of the pair potential at the sample surfaces is the cause of the deviations of our I/sub c/R/sub N/ from ideal BCS value.<>