Epitaxial YBa2Cu3O7-8 films : Crucial role of growth-induced linear defects in microwave properties

A significant contribution to high-frequency electromagnetic response of epitaxial YBCO films is supposed to be accounted for growth-induced linear defects. There are two major types of linear defects in the YBCO films : out-of-plane and in-plane edge dislocations. The out-of-plane edge dislocations are shown to play a remarkable role in the surface resistance due to their extended elastic strain fields around a normal core. In-plane edge dislocations do not contribute observably into HF losses, since strain fields around their cores are negligible. The area of suppressed order parameter per one dislocation line was estimated to be 8.10-13) cm2 at 77 K. When out-of- plane edge dislocation density is 1011 lines/cm2, the normal phase fraction in the film volume can reach approximately 10%. The heat instability induced by the linear defects is assumed to enhance the remarkable difference between microwave properties of YBCO single crystals and thin films and results in a nonlinear response