Third-order local nonlinear microwave response of YBa2Cu 3O7 and Nb thin films

HTS thin films continue to be of interest for passive device applications at 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 inductive 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 dc-magnetic field on some places of the film. The temperature dependence demonstrates 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~1.5-3. The correlation between the depinning current density J_p and the nonlinear microwave response is also demonstrated