Self-organized criticality induced by quenched disorder: experiments on flux avalanches in NbH$_x$ films

TL;DR

This study demonstrates that quenched disorder in NbH$_x$ superconducting films induces self-organized criticality, characterized by power-law distributed flux avalanches with fractal shapes, unlike the smooth avalanches in less disordered samples.

Contribution

The paper provides experimental evidence linking quenched disorder to SOC behavior in superconductors, highlighting the role of disorder in avalanche size distribution and shape.

Findings

Avalanche sizes follow a power-law distribution with finite size scaling.

Fractal shape observed in avalanches with high disorder.

Absence of disorder results in smooth, preferred-size avalanches.

Abstract

We present an experimental study of the influence of quenched disorder on the distribution of flux avalanches in type-II superconductors. In the presence of much quenched disorder, the avalanche sizes are power-law distributed and show finite size scaling, as expected from self-organized criticality (SOC). Furthermore, the shape of the avalanches is observed to be fractal. In the absence of quenched disorder, a preferred size of avalanches is observed and avalanches are smooth. These observations indicate that a certain minimum amount of disorder is necessary for SOC behavior. We relate these findings to the appearance or non-appearance of SOC in other experimental systems, particularly piles of sand.