ANGULAR-DEPENDENCE OF MICROWAVE DISSIPATION BY VORTICES IN YBA2CU3O7-X THIN-FILMS

Using meander line resonant structures, we perform highly sensitive me asurements of the changes in surface resistance Delta R(s) of YBa2Cu3O 7-x thin films in order to probe the vortex dynamics as a function of temperature, applied de magnetic field, and angle (theta) of the appli ed field relative to the ab planes. We observe that the component of t he magnetic field normal to the planes produces substantially more dis sipation than the component parallel to the planes. By using an extens ion of the London theory to anisotropic superconductors, we can calcul ate the internal flux densities parallel (B-ab) and perpendicular (B-c ) to the ab planes inside a superconductor for an arbitrary field orie ntation relative to the ab planes. For low fields, we can define a wei ght (delta) of the contribution to dissipation from B-ab relative to t hat from B-c. This allows us to calculate an ''effective'' internal fl ux density and hence obtain the total dissipation. Using the results f rom this theory, we obtain excellent quantitative agreement with our m easurements of Delta R(s) vs theta.