Josephson tunneling studies of magnetic screening in proximity effect superconductors

The periodic magnetic field dependence of the dc Josephson current has been used to study the magnetic screening properties of proximity effect superconductors. A series of junctions of the S-I-N-S' geometry have been measured for which the normal metal layers have been silver, tin, and aluminum. The effective magnetic penetration depth has been studied as a function of normal metal thickness, temperature, and composition of the N-S' sandwich both in a helium-4 cryostat and in a helium-3-4 dilution refrigerator. Thickness and temperature effects have been explained with good agreement by a numerical calculation and a characteristic penetration depth for each N-S' couple has been found that is independent of normal metal thickness and inversely proportional to the energy gap of the backing superconductor