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 ${\lambda }_{\mathrm{eff}}$(T) reveal that unconventional penetration depth temperature dependences, such as Δ${\lambda }_{\mathrm{eff}}$(T)∼T found in ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ crystals, are qualitatively reproduced with this model.