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In this paper, we characterize microwave nonlinearity in a high temperature superconducting (HTS) thin-film by measuring a geometry-independent current-density scale . The quantity specifies the strength of a material-dependent nonlinearity, and can be used to calculate the nonlinear microwave response of planar superconducting transmission-line devices. Our procedure for determining involves microwave measurements on superconducting coplanar waveguide devices patterned onto the HTS sample. In a YBa 2 Cu 3 O 7 x (YBCO) sample, we obtained a maximum experimental value for of approximately 3 26 10 8 A cm 2 at 25 K. From the measured temperaturedependence of in our YBCO sample, and assuming a theoretical pair-breaking current density equal to 3 10 8 A cm 2 , we calculated the temperature dependence of the quasiparticle factor ( ). The curve of the experimentally obtained ( ) matched well with a theoretically-predicted behavior in the scenario of d-wave symmetry in the superconducting order parameter.

We present new frequency-dependent measurements of both the magnitude and phase of the nonlinear response in superconducting thin films at microwave frequencies obtained using a large-signal network analyzer. Our measurements show that the nonlinear inductance dominates the nonlinear response in thin YBCO films at 76 K, and our analysis yields two current-density scales corresponding to the real and imaginary components of the nonlinear response. The current-density scale associated with the dominant inductive response likely results from intrinsic pair-breaking, while the current-density scale associated with the nonlinear resistive term is smaller than the expected value due to pair-breaking, and could originate from vortex motion or other extrinsic effects.Index Terms-High-temperature superconductivity, microwave frequency, nonlinear response.