RESISTANCE FLICKER NOISE AND CURRENT PERCOLATION IN C-ORIENTED YBA2CU3O7-X FILMS IN THE VICINITY OF T-C

Noise properties of c-oriented YBa2Cu3O7-x films near T-c have been in vestigated both experimentally and theoretically. The films studied ar e divided into two groups. The resistance noise and transport properti es for the films (1) are controlled by the grain boundary junctions. T he films (2) are of high structural perfection and have very low nicke r noise levels. Their S-R(T)-characteristics near T-c are quantitative ly described by a novel percolation model. The model takes into accoun t static T-c-inhomogeneities of the film and the presence of defects t hat modulate the local T-c. Distribution functions of T-c were obtaine d and defect density of states as well as a scale of T-c-relief were e stimated. The spatial current distribution is studied by low-temperatu re SEM. The method is originally used for T-c-mapping of the films. A special algorithm for the LTSEM data treatment for inhomogeneous films using the effective medium approach and allowing us to derive local t ransition curves is proposed.