Magneto-depending noise of a single latent weak link in YBa 2Cu 3O 7− x film

Abstract

The voltage noise and current inhomogeneities in a thin c oriented YBa 2Cu 3O 7− x film on a MgO substrate have been investigated. An unusually sharp peak of the low-frequency noise was 7 K below T c observed with a width of less than 1 K and a strongly nonmonotonical dependence on external magnetic field. The appearance of this peak is found to be related to a single defect which leads to the formation of a weak link in the bottleneck of the current percolation path. This weak link is a latent one; it is undetectable by the standard characterization aechniques and has no effect on the integral transport properties of the film. We were able to reveal it using low-temperature scanning electron microscopy which allowed us to determine the current-density distribution across the weak link with a resolution of < 1 μm. The critical current density of the weak link is found to be j c (77 K) > 5 x 10 6 A/cm 2 which is comparable with the critical current density of high-quality YBaCuO films. Analysis of the experimental dependences in terms of the resistively shunted junction model shows that Abrikosov vortex motion is involved resulting in fluctuations of the phase difference across the weak link leading to a peak of the voltage noise at the temperature at which the current through the weak link is close to its critical current.