Flux avalanches in a Josephson medium

Avalanche flux penetration dynamics has been experimentally observed in a Josephson medium, a granular high-T _c superconductor, with a slowly increasing external magnetic field. The observed voltage spikes are associated with the stepwise penetration of the field into the superconductor and obey a power-law size distribution. The results directly confirm the hypothesis of self-organized criticality in such a system.