REDUCTION OF THE ANDREEV SCATTERING PROCESSES IN ULTRA-SMALL SUPERCONDUCTING POINT CONTACTS WITH DIRECT CONDUCTIVITY

We report on measurements using ultra-small superconducting point contacts, variable in size, with electrodes formed with the elements Pb, Nb, Sn, In and Ta. We focus on the behavior of the critical current-normal resistance product as a function of constriction size. When normalized to the gap value, a material-independent, uniform reduction of this product is found when the constriction size is reduced towards atomic dimensions. We present a description, where the destruction of interference from Andreev reflected particles in the contact leads to a reduction of the critical current, thus explaining the reduction of the critical current-normal resistance product.