ANDREEV REFLECTIONS AND JOSEPHSON EFFECTS IN POINT CONTACTS BETWEEN THE HEAVY-FERMION SUPERCONDUCTOR URU2SI2 AND CONVENTIONAL SUPERCONDUCTORS

We have studied the dV/dI vs. V characteristics of point contacts betw een the heavy fermion superconductor URu2Si2 and the conventional supe rconductors Zn and NbTi. Contacts between URu2Si2 and Zn do not show J osephson effects; instead Andreev reflection type structures occur, wh ich are related to both, the heavy fermion and the conventional superc onductor. In contrast, contacts between URu2Si2 and NbTi become superc onducting at low currents. A closed-loop setup with two NbTi contacts on URu2Si2 showed SQUID oscillations in a small magnetic field. Our da ta give evidence that the contacts should be described as superconduct or/ normal/superconductor junctions with a thick normal layer on the U Ru2Si2 side of the contact with proximity induced superconductivity in the N-layer in the case of NbTi. With such a model the occurrence or absence of superconductivity can be explained and also the suppression of Andreev-scattering which is frequently observed for contacts betwe en heavy fermion superconductors and normal metals.