THE ROLE OF THE SURFACE DEPRESSION OF THE PAIR POTENTIAL ON THE JOSEPHSON AND QUASI-PARTICLE TUNNELING IN HIGH-T-C SUPERCONDUCTORS

We discuss the influence of the intrinsic surface depression of the or der parameter on the temperature dependence of the Josephson critical current I-c(T) and, tentatively, on the quasi-particle tunnelling cond uctance in a superconductor with a very short coherence length. The co mparison with the experiments shows that the presence of a surface-dep ressed pair potential can explain the large deviations of the I-c(T) f rom the ideal BCS behaviour that we recently observed in Bi2Sr2CaCu2O( 8+x) Josephson break junctions and could mimic the presence of a broad ening in the Superconductor-Insulator-Normal tunnelling conductance of the same high-T-c superconductor.