Avalanches and Slow Relaxation: Dynamics of Ultrathin Granular Superconducting Films in a Parallel Magnetic Field

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Abstract
We report unusual dynamics of ultrathin granular Al films in the hysteretic region near the parallel critical field. Avalanches in film resistance, corresponding to the collapse of macroscopic superconducting regions, are observed. As films approach the normal state, large avalanches give way to slow, stretched-exponential decay interspersed with smaller avalanches. The size distribution of the avalanches exhibits power-law behavior over three decades. We discuss the origins of the avalanches and the slow relaxation in terms of a 2D random array of Josephson junctions.