GRANULAR SUPERCONDUCTORS AND THEIR INTRINSIC AND EXTRINSIC SURFACE IMPEDANCE

High-frequency experiments depend sensitively on homogeneous and inhom ogeneous ''defects'' in the normal and superconducting state. As homog eneous effects, the intrinsic scattering time is of great theoretical importance above 0.1 THz in the surface impedance Z. Of practical impo rtance are the planar defects, ''the weak links (WL),'' which interrup t the rf shielding currents and thus enhance Z(eff). In the supercondu cting state, the Josephson current j(cJ) crosses the WL in parallel wi th 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 increas ing field, Z deteriorates like H-2 up to H-clJ, where Josephson fluxon s (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 hysteres is losses and reactive components. The nonlinear JF effects are enforc ed by thin-film edge enhancements limiting the performance of various devices by enhanced dissipation, reactance, and flux noise. A method i s presented which is able to separate electron dynamics at the WL from their strength and distribution.