Andreev scattering in nanoscopic junctions in a magnetic field

We report on the measurement of multiple Andreev resonances at atomic size point contacts between two superconducting nanostructures of Pb under magne tic fields higher than the bulk critical field, where superconductivity is restricted to a mesoscopic region near the contact. The small number of con duction channels in this type of contacts permits a quantitative comparison with theory through the whole field range. We discuss in detail the physic al properties of our structure, in which the normal bulk electrodes induce a proximity effect into the mesoscopic superconducting part.