Microwave breakdown initiated in a high-temperature superconducting film by thermal disturbances and defects

The effect of thermal disturbances and nonsuperconducting defects on the mi crowave breakdown of a high-temperature superconducting film is investigate d theoretically. The dependence of the critical energy of thermal disturban ces on the surface microwave field is obtained. It is shown that in a wide range of values of the surface microwave field the critical energy of local disturbances is less than the critical energy of spatially extended distur bances. It is established that microwave breakdown on defects may be preced ed by a stage of formation of a finite-size normal-phase region localized a t the defect. The effect of the form and absorption coefficient of the defe ct on scenarios leading to the destruction of superconductivity and on the microwave breakdown field of a film at a defect are investigated. (C) 1999 American Institute of Physics. [S1063-7842(99)00905-8].