The effective surface resistance of superconductor/dielectric/metal structures

We investigate the effective microwave surface resistance of superconductor/dielectric/normal metal structures through numerical simulations. In particular, the setup with a thin superconducting film on a dielectric substrate, backed by a metallic endplate, is analysed. The results demonstrate that the effects of the substrate on the measured surface resistance of superconducting thin films must be taken into account. We show that in this setup several spurious effects are predicted. At characteristic frequencies, dependant on the substrate material, the commonly used thin-film approximation fails even for films thinner than the London penetration depth. In general, when the film is thicker than, but of the same order as, λ, the measured surface resistance can exceed both the thin-film and the bulk values. We investigate how the effective surface resistance of a superconducting film can be approximated by the bulk or the thin-film value, as a function of frequency, film and substrate thickness, and temperature. We exploit a thin-film model to take into account the effects of the backing materials. Measurements of surface resistance are performed on a BSCCO/SrTiO3/metal structure to stress the nonintrinsic behaviours and to test the proposed model. (author)