Magnetic screening in proximity-coupled superconductor/normal-metal bilayers

The electrodynamics of a metallic surface layer in proximity contact to a superconductor are considered. The surface region is modeled as an idealized proximity-coupled superconductor/normal-metal (S/N) bilayer. Analytical expressions for the magnetic-field penetration into the sample are obtained. The behavior of the model and its applicability to magnetic-screening-length measurements on artificial and naturally occurring S/N bilayer superconductors are discussed in various limits. Calculations of the effective penetration depth λ_eff(T) reveal that unconventional penetration depth temperature dependences, such as Δλ_eff(T)∼T found in YBa₂Cu₃O_7-δ crystals, are qualitatively reproduced with this model.