Power-dependent impedance of high temperature superconductor thin films: Relation to harmonic generation

We present measurements of the power-dependent microwave surface impedance of YBa2Cu3O7-delta thin films, performed using patterned coplanar waveguide (CPW) resonators at 5.87 GHz and 76 K. We compare these resonator measurem ents with third-harmonic generation measurements performed on CPW transmiss ion lines of the same geometry patterned onto the same thin-film sample at the same frequency and temperature. We find that the power-dependent surfac e reactance X-s(P-rf) is directly related to the magnitude of the generated third-harmonic signal, indicating a common origin fur both of these manife stations of nonlinearity in high temperature superconductor (HTS) devices. These results are consistent with the nonlinear response generated by a cur rent-dependent penetration depth lambda (J), which provides a material limi tation on the linearity that can be achieved in any practical HTS microwave device.