NONLINEAR ELECTRODYNAMICS OF YBA2CU3O7 THIN-FILMS IN THE MICROWAVE REGION

We report on investigations of the nonlinear behavior of thin films of YBa2Cu3O7 by the method of phase-resolved microwave harmonic mixing both with and without an applied static magnetic field at low microwave power levels. Temperature dependent measurements on high quality films show that nonlinearities appear only in the superconducting transition region. The dependence of the nonlinear signal on the microwave field strength E(omega) exhibits an E(omega)2.2-power law. No dependence on the strength of a magnetic field up to 300 G was found. The mixing results are compared to those of harmonic generation experiments done by other groups. The possible mechanisms for the nonlinear behavior are discussed.