Temperature dependence of the surface resistance R(T,/spl omega/) and mean free path l(T) of YBCO-superconductors

The surface resistance R(T/spl omega/) at 10 and 145 GHz is obtained experimentally between 4 and 300 K. In the temperature range T/sub a//spl les/T/spl les/T/sub c/ R(T) is quantitatively fitted by the BCS theory with a mean free path l(T) increasing exponentially below T/sub c/. The l(T)-increase is related to diminishing plane-chain scattering and is limited at T/sub a/ by "inelastic surface scattering" at weak or strong links, e.g., at twin boundaries of an average distance a/sub TW/. They dominate scattering for l(T)/spl ges/a/sub TW//2. Below T/sub a/ the enforced energy transfer from YBCO-crystallites to weak links enhances R(T