Intrinsic high-T-c Josephson junctions in random-telegraph-noise fluctuators

Bias current and magnetic field strongly influence the switching rates of random-telegraph signals by stressing the two-level fluctuator energy structure. Symmetric-telegraph noise is observed when the stress due to current flow is compensated by the magnetic-field-induced stress. The dependence of the measured symmetrizing magnetic field on current flow enables one to infer the symmetry characteristics of a fluctuator. The symmetry characteristics in granular films were found to be strongly nonlinear. It has been shown that current flow across the intrinsic Josephson inductance is responsible for the observed nonlinearity. A fit of the experimental data to the proposed model has revealed that a Josephson element enclosed in a superconducting loop is likely involved in the random-telegraph voltage noise generation. The evaluated area of the loop is consistent with the free space between average grains in the sample investigated.