NOISE DEPENDENCE ON MAGNETIC-FIELD IN GRANULAR BULK HIGH-T-C SUPERCONDUCTORS

The increase in voltage noise observed by increasing magnetic field in granular high-T-c superconductors is explained in the framework of a percolative model. Noise is reproduced with computer simulations of a network of junctions, many of which are randomly shorted. The network configuration is representative of interconnections (weak links) of gr ains in polycrystalline bulk samples. With respect to previous percola tive models, we have demonstrated that the calculated noise intensity is modified when interdependence between different configurations in t he time evolution of the network is considered. The concordance with t he experimental dependence of noise on resistance at different magneti c field intensities in YBa2Cu3O7-delta and HgBa2CuO4+delta supports th e hypothesis that magnetic field affects the fluxon speed and thus the switching rate of weak links.