OBSERVATION OF A NONOHMIC COMPONENT OF SP ONTANEOUS CONDUCTIVITY FLUCTUATIONS IN YBA2CU3O7-X THIN-FILMS

Resistive and noise properties of thin single-crystal YBa2Cu3O7-x film s with the c axis being parallel to the substrate plane have been stud ied. In the normal state as well as in the region of the superconducti ng transition we observed variations of the resistance fluctuation spe ctral density with current, which is direct evidence of structure elem ents with nonlinear current-voltage relationships present in high-T(c) materials. On the basis of a comparison of data for c(parallel-to)- a nd c(perpendicular-to) - films, certain inferences are made about the microscopic origin of the structure elements, responsible for the curr ent nonlinearities in the noise properties of HTSC.