MICROWAVE AND RADIOWAVE SURFACE-RESISTANCE OF HIGH-QUALITY YBACUO CERAMIC - NONLINEAR ASPECTS

An unusual microwave magnetic-field amplitude H-omega dependence of th e 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 supercon ductor in the current-induced critical state. A good agreement of the experimental dependence of R(s) on H-omega with Gurevich's theory of t he nonlinear dynamics of vortices in high-J(c) overdamped Josephson co ntacts 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 simult aneously with R(s)(mw)(H-omega) was found to obey the same law. Temper ature and DC magnetic field dependences of R(s) in both frequency rang es have also been investigated. The temperature dependence of the crit ical current density has been extracted from the radiowave absorption. Possible physical origins of the observed nonlinear effects are brief ly discussed.