Microwave properties of YBa2CU3O7-delta films: magnetic-field-dependent order parameter fluctuations

We present measurements of the microwave resistivity in YBa2Cu3O7-delta fil ms as a function of the temperature and magnetic field at 48 GHz above the critical temperature T-c. Even in moderate fields (up to 0.7 T) a noticeabl e magnetodissipation is observed; we attribute this to order parameter fluc tuations. We find that Gaussian fluctuations are not consistent with the ob served behaviour. Starting from the fact that the measurements taken in zer o magnetic held can be quantitatively described in terms of the three-dimen sional anisotropic renormalized fluctuations theory, we phenomenologically extend the theory by assuming that (to the first order in the magnetic fiel d) the effects of renormalization reduce to the introduction of a temperatu re-dependent field scale. In this way we obtain a quantitative description of the experimental field-dependent microwave resistivity.