Mixed-state microwave response in superconducting cuprates

We report measurements of the magnetic field induced microwave complex resistivity in REBa2Cu3O7-delta thin films, with RE = Y, Sm. Measurements are performed at 48GHz by means of a resonant cavity in the end-wall-replacement configuration. The magnetic field dependence is investigated by applying a moderate (0.8 T) magnetic field along the c-axis. The measured vortex-state complex resistivity in YBa2Cu3O7-delta and SmBa2Cu3O7-delta is analyzed within the well-known models for vortex dynamics. It is shown that attributing the observed response to vortex motion alone leads to inconsistencies in the as-determined vortex parameters (such as the vortex viscosity and the pinning constant). By contrast, attributing the entire response to field-induced pair breaking leads to a nearly quantitative description of the data.