Josephson tunneling studies of magnetic screening in proximity- superconducting silver

The diamagnetic properties of silver backed by a thick lead layer have been studied as a function of normal-metal thickness and of temperature. Data were obtained by measuring the period of the magnetic field dependence of the critical Josephson current in S-I-N-S tunnel junctions. Strong screening has been seen at low temperatures and a thickness-independent penetration depth is indicated as the temperature goes to zero. This characteristic penetration depth is observed to be on the order of 1500 for proximity-effect silver. We have used a modified London equation for the case of a spatially varying pair amplitude and have numerically solved for the magnetic field profile in this system. The spatial dependence of the pair amplitude obtained from Landau-Ginzburg theory produces good agreement with thickness- and temperature-dependence data.