Third-order local nonlinear microwave response of YBa2Cu3O7 and Nb thin films

HTS thin films continue to be of interest for passive device applications a t microwave frequencies, but nonlinear effects may limit their performance. We report a set of experimental data on local third-harmonic generation at microwave frequencies (0.5 GHz) in YBa2Cu3O7 and Nb thin films from 4.2 K to T-c. For local investigations of the nonlinear response a probe with ind uctive coupling was developed. The map of the nonlinear microwave response of YBa2Cu3O7 thin film is plotted below T-c with high resolution. The third -harmonic power is measured as a function of temperature, input power and d e magnetic field on some places of the film. The temperature dependence dem onstrates a peak of nonlinearity below T-c for YBa2Cu3O7 and Nb films and a minimum of nonlinearity at low temperatures for HTS films. The behavior of the third-harmonic power vs the input power can be described by the power- law with the exponent n similar to1.5-3. The correlation between the depinn ing current density J(p) and the nonlinear microwave response is also demon strated.