Abstract
The leading indicator for quality in rf superconductivity are: the weak link (WL) density and their quality which is given by critical current j cJ(T≈O, B≈O), Josephson penetration depth λ J∝1/√j cJ and normal (leakage) tunnel current j bl. The j cJ(T,B)- and j bl(T)-values explain penetretion depth λ res and surface resistance R res ⋍ (ωμ o) 2λ J 3 j bl/2 quantitatively and in temperature ∝(a + T n), n ≈ 1, and ∝(b + H n); n ≈ 1 H > H c1J in field dependence. Here H c1J is the field where Josephson fluxons penetrate into WL's enhancing the penetration depth and thus the rf residual losses. For thinner films t < λ J, R res is enhanced further by λ J/t and field dependencies are changed by enlarged penetration depths λ⊥ J = λ J 2/2t, by flux focusing and by demagnetization.
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