Anisotropic properties of the microwave magneto-dissipation in high-T c superconducting films

We report measurements of the magnetic field dependent microwave dissipation at 21 GHz in Bi2Sr2CaCu2O8+x epitaxial films and in oriented YBa2Cu3O7−σ films, by means of the end-wall-replacement cavity technique. The power reflected by the tuned cavity is measured as a function of the external magnetic fieldH and of the angle e betweenH and the (a, b), planes, at fixed temperatures. In Bi2Sr2CaCu2O8+x , apart from a narrow (Δe≈0.5°) angular range close to the parallel orientation, the strongly anisotropic dissipation exhibits striking scaling properties: all the data at fixed temperature can be made to collapse on a single curve with a simple angular scaling of the magnetic field:H→H/f(e). It is found that the anisotropy ratiof(0°)/f(90°) increases with temperature. It is shown that the scaling functionf(e) and its temperature evolution are in agreement with the model for a quasi-2D superconductor. In YBa2Cu3O7-σ the presence of the flux-flow dissipation prevents the application of a scaling procedure, and a specific model must be applied. We obtain that the anisotropy is almost constant with the temperature, as predicted for a three-dimensional, anisotropic superconductor.