FLUX PINNING AND VORTEX DYNAMICS IN HIGH-T(C) SUPERCONDUCTING FILMS

The field dependences of the critical current, current-voltage charact eristics and a.c. susceptibility have been investigated for supercondu cting YBa2Cu3O7 films prepared by laser ablation. It was shown that th e flux line pinning in polycrystalline high T(c) films occurs due to a nisotropy of the superconducting parameters in the case of strong miso rientation of adjacent grains and that it is connected with local supp ression of the order parameter for smaller misorientation angles. Pecu liarities of the resistive state in magnetic fields have led us to sup pose that vortex motion occurs preferably along the grain boundaries, which form a network of so-called easy slip channels. Such microstruct ural features of the tested films lead to the double-peak behaviour of the dissipative part of the a.c. susceptibility.