Low frequency resistance fluctuations in films of high temperature superconductors

Low-frequency voltage fluctuations in thin films of YBa 2 Cu 3 O 7-x at and above the superconducting transition temperature have a spectral density proportional to the ratio of the average voltage across the film to the frequency. The ratio of the spectral density to the average voltage decreases markedly as the microstructure of the films is improved. In contrast to classic superconductors, the noise at the resistive transition does not arise from equilibrium temperature fluctuations