Third-order local nonlinear microwave response of YBa/sub 2/Cu/sub 3/O/sub 7/ and Nb thin films

Abstract

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 YBa/sub 2/Cu/sub 3/O/sub 7/ and Nb thin films from 4.2 K to T/sub c/. For local investigations of the nonlinear response a probe with inductive coupling was developed. The map of the nonlinear microwave response of YBa/sub 2/Cu/sub 3/O/sub 7/ thin film is plotted below T/sub 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/sub c/ for YBa/sub 2/Cu/sub 3/O/sub 7/ 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/spl sim/1.5-3. The correlation between the depinning current density J/sub p/ and the nonlinear microwave response is also demonstrated.