Angular dependence of microwave dissipation by vortices in YBa2Cu3O7-x thin films.

Abstract

Using meander line resonant structures, we perform highly sensitive measurements of the changes in surface resistance {Delta}{ital R}{sub {ital s}} of YBa{sub 2}Cu{sub 3}O{sub 7{minus}{ital x}} thin films in order to probe the vortex dynamics as a function of temperature, applied dc magnetic field, and angle ({theta}) of the applied field relative to the {ital 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. By using an extension of the London theory to anisotropic superconductors, we can calculate the internal flux densities parallel ({ital B}{sub {ital a}{ital b}}) and perpendicular ({ital B}{sub {ital c}}) to the {ital ab} planes inside a superconductor for an arbitrary field orientation relative to the {ital ab} planes. For low fields, we can define a weight ({delta}) of the contribution to dissipation from {ital B}{sub {ital a}{ital b}} relative to that from {ital B}{sub {ital c}}. This allows us to calculate an ``effective`` internal flux density and hence obtain the total dissipation. Using the results from this theory, we obtain excellent quantitative agreement with our measurements of {Delta}{ital R}{sub {ital s}} vs {theta}.