We study experimentally the low temperature resistance of superconducting nanowires connected to normal metal reservoirs. We find that a substantial fraction of the nanowires is resistive, down to the lowest temperature measured, indicative of an intrinsic boundary resistance due to the Andreevconversion of normal current to supercurrent. The results are successfully analyzed in terms of the kinetic equations for diffusive superconductors.

Abstract. -We have investigated the proximity effect between a superconductor (Nb) and a 'Heavy Fermion' system (CeCu6) by measuring critical temperatures Tc and parallel critical fields H c2 (T) of Nb films with varying thickness deposited on 75 nm thick films of CeCu6, and comparing the results with the behavior of similar films deposited on the normal metal Cu. For Nb on CeCu6 we find a strong decrease of Tc with decreasing Nb thickness and a finite critical thickness of the order of 10 nm. Also, dimensional crossovers in H c2 (T) are completely absent, in strong contrast with Nb/Cu. Analysis of the data by a proximity effect model based on the Takahashi-Tachiki theory shows that the data can be explained by taking into account both the high effective mass (or low electronic diffusion constant), and the large density of states at the Fermi energy which characterize the Heavy Fermion metal.