High frequency resistivity in YBa2Cu3O7-delta: Effects of anisotropic renormalized fluctuations

We discuss the excess conductivity above T-c due to renormalized order-para meter fluctuations in YBCO at microwave frequencies. We show that a phenome nological cut-off in the fluctuative spectrum can extend the results of the anisotropic theory of renormalized fluctuations up to the high temperature region. Measurements of the real part of the microwave resistivity at 24 G Hz are performed on two YBCO films. The onset of the superconducting transi tion and the deviation from the linear temperature behavior carl be fully a ccounted for by the extended theory. Very consistent values of the fundamen tal parameters (critical temperature, coherence lenghts, penetration depth) of the superconducting state are obtained.