Microwave losses induced by vortex propagation in highly epitaxial YBa2Cu3O7-delta films

The rf and microwave losses of devices based on YBa2Cu3O7-delta superconduc ting films are dominated by extrinsic mechanisms that can be controlled by a careful device fabrication and design. Often the granular nature of the f ilms shows up in the measurements of the residual surface resistance. We ha ve measured the surface impedance of a large number of highly epitaxial, de sputtered YBa2Cu3O7-delta films patterned by argon ion milling as meanderl ine microstrip resonator (T-c>90K and DeltaT(c)<1K). The plot of R-s vs. H- rf shows that the excess surface resistance is determined by Josephson vort ices propagating in the grain boundaries, in good agreement with the theore tical prediction of Halbritter. Further, the temperature and frequency depe ndence of Z(s) is consistent with this hypothesis.