Microwave and radiowave surface resistance of high-quality YBaCuO ceramic. Nonlinear aspects

An unusual microwave magnetic-field amplitude H-omega dependence of the microwave (35 GHz), surface resistance R(s)(mw) and radiowave (9 MHz) response on the microwave irradiation of an YBa2Cu3O7-delta ceramic has been found. The observed behavior is consistent with the model of Sridhar for the nonlinear high-frequency response of a planar superconductor in the current-induced critical state. A good agreement of the experimental dependence of R(s) on H-omega with Gurevich's theory of the nonlinear dynamics of vortices in high-J(c) overdamped Josephson contacts has been also observed. The radiowave response Delta R(s)(rf) = R(s)(rf)(H-omega) - R(s)(rf)(0) dependence on H-omega measured simultaneously with R(s)(mw)(H-omega) was found to obey the same law. Temperature and DC magnetic field dependences of R(s) in both frequency ranges have also been investigated. The temperature dependence of the critical current density has been extracted from the radiowave absorption. Possible physical origins of the observed nonlinear effects are briefly discussed.