Microwave dissipation due to vortices in YBa/sub 2/Cu/sub 3/O/sub 7-x/ thin films for magnetic fields applied at small angles from the ab-planes

Abstract

YBa/sub 2/Cu/sub 3/O/sub 7-x/ thin films patterned in a meander line resonant structure are used to probe vortex dynamics at microwave frequencies. We perform highly sensitive measurements of the changes in surface resistance /spl Delta/R/sub s/(H,T,/spl theta/) of YBa/sub 2/Cu/sub 3/O/sub 7-x/ thin films as a function of applied dc field, temperature, and angle of the applied field relative to the ab-planes. We observe that the component of the magnetic field normal to the planes produces substantially more dissipation than the component parallel to the planes. Also, the surface resistance R/sub s/ vs. H data for magnetic fields applied at small angles from the ab-planes shows two regions of markedly different field dependence separated by a crossover field H*. For applied fields H>H* we have linear dependence of R/sub s/ on applied field with a steep slope. For applied fields H<H*, we observe a much smaller slope in the RS versus field data. We believe that the low field region corresponds to the case where we have complete shielding of the field from the ab-planes (transverse Meissner effect), such that the field lines do not cross them and are instead confined to the interplanar region.<<ETX>>