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 b oth with and without an applied static magnetic field at low microwave power levels. Temperature dependent measurements on high quality film s show that nonlinearities appear only in the superconducting transiti on region. The dependence of the nonlinear signal on the microwave fie ld 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 ar e discussed.