Surface behavior of the gap parameter in short-coherence-length superconductors: Photoemission and critical currents

We examine how the behavior of the gap parameter near the boundary between a short-coherence-length superconductor and an insulator can be studied by using several experimental probes. We show how photoemission can be used directly to infer the profile of the gap near such a boundary. We show that photoemission and critical-current experimental results for high-temperature superconductors are all indicative of a nondepleted gap near the surface. This is inconsistent with standard Ginzburg-Landau results, but in agreement with recent microscopic calculations.