Evidence for self-organized criticality in the Bean critical state in superconductors

The time dependence of the magnetization of a type-Il superconductor in the Bean critical state is studied. It is found that evolution occurs in the form of bursts, consistent with a model exhibiting self-organized criticality. The distribution of step sizes follows a power law with an exponent of alpha similar or equal to 2. At high temperatures the distribution is Gaussian-like, as would be expected in an equilibrium situation. This may allow the experimental study of the occurrence of criticality.