Observation of a non-Ohmic component of spontaneous conductivity fluctuations in Y Ba2 Cu3 O7-x thin films

Resistive and noise properties of thin single-crystal Y Ba2 Cu3 O7-x films with the c axis being parallel to the substrate plane have been studied. In the normal state as well as in the region of the superconducting transition we observed variations of the resistance fluctuation spectral density with current, which is direct evidence of structure elements with nonlinear current-voltage relationships present in high-Tc materials. On the basis of a comparison of data for cparallel - and cperpendicular -films, certain inferences are made about the microscopic origin of the structure elements, responsible for the current nonlinearities in the noise properties of HTSC