Granular superconductors and their intrinsic and extrinsic surface impedance

High-frequency experiments depend sensitively on homogeneous and inhomogeneous ''defects'' in the normal and superconducting state. As homogeneous effects, the intrinsic scattering time is of great theoretical importance above 0.1 THz in the surface impedance Z. Of practical importance are the planar defects, ''the weak links (WL),'' which interrupt the rf shielding currents and thus enhance Z(eff). In the superconducting state, the Josephson current j(cJ) crosses the WL in parallel with the normal, leakage current j(bl). The latter explains the observed, finite rf residual losses R(res)(T approximate to 0) quantitatively and as a function of material parameters, temperature T, field H, and frequency omega for Nb, NbN, and cuprate superconductors. With increasing field, Z deteriorates like H-2 up to H-clJ, where Josephson fluxons (JF) penetrate into the WL yielding delta Z proportional to H. Above H-clJ approximate to 0.1-10 mT, JF dynamics dominates Z with hysteresis losses and reactive components. The nonlinear JF effects are enforced by thin-film edge enhancements limiting the performance of various devices by enhanced dissipation, reactance, and flux noise. A method is presented which is able to separate electron dynamics at the WL from their strength and distribution.