Point contact spectroscopy: a powerful technique for the low temperature characterization of superconducting materials

We describe the Point Contact Spectroscopy technique for the characterization of superconducting materials. By pushing a metallic tip on the superconducting surface, it is possible to tune the interface properties, from a perfect transparent barrier up to the case of insulating barrier separating the two electrodes of a tunnel junction. The experiments can be described in the framework of Blonder-Tinkham-Klapwijck theory. In this paper, we show both cases, observed on two different kinds of superconductors and compare the results with the theory.