Non-ohmic dissipation in granular YBCO films with microwave radiation

The evidence for nonequilibrium response to microwave radiation (37 GHz) fr om YBa2Cu3O7-delta (YBCO) granular films is presented in this paper. The ex perimental results show that the microwave response always occurs within th e "tail" region in R-T curves. The measurements of the I-V characteristics suggest that the dissipation below the G-L mean field transition temperatur e T-co can be described in terms of the Kosterlitz-Thouless (K-T) transitio n model, Based on the measurements with a weak magnetic field. we propose t hat the origin of the nonequilibrium microwave response in granular YBCO fi lms may be related with the photon-vortex interaction process. (C) 1999 Els evier Science B.V. All rights reserved.