Evidence for a distribution of discrete energy gaps in polycrystalline high-Tc superconductors.

Abstract

We present measurements of the differential conductance dI/dV versus V of normal-metal-high-T c ceramic point contacts. We have found that the measured curves can be interpreted by considering two effects: an asymmetric tunneling barrier and a set of distinct superconducting energy gaps. We show that the BCS density of states, modified by introducing a Gaussian discrete distribution of gap values, yields a very good fit of the experimental curves