Flux-flow and fluctuations in the microwave resistivity of YBa2Cu3O7-delta

We present measurements of the microwave resistivity at 48 GHz in YBa2Cu3O7 -delta film, as a function of the temperature and the magnetic field. The m agneto-dissipation from 60 K up to a few kelvins below T-c finds a quantita tive description in terms of free flux flow. Approaching T-c, the data are not consistent with a dissipative mechanism based solely on flux dynamic. F luxon viscosity is measured as a function of the temperature, and the in-pl ane coherence length is estimated. The analysis of the zero-field transitio n at 48 GHz in terms of anisotropic renormalized fluctuations yields identi cal estimate.