Angular dependence of current-voltage characteristics and voltage fluctuation spectrum in granular superconductors

The current-voltage characteristics (CVC) and the voltage noise spectrum S- v(f) of YBa2Cu3O7-delta ceramic superconductors have been measured in relat ion to the angle between the magnetic field and current direction in low ma gnetic fields at various temperatures. The angular dependence of the fluctu ation spectrum has been studied for the first time. It is shown that the fl ux-line-cutting model fails to describe the experimental CVCs, and the volt age fluctuations disagree with the predictions of the model in which vortic es move in the sample independently. The results obtained are consistent wi th the self-organized isotropic critical state model.