Self-organized criticality in the Bean state in YBa2Cu3O7 − x thin films

The penetration of magnetic flux into a thin film of YBa2Cu3O7 − x is studied when the external field is ramped slowly. In this case, the flux penetrates in bursts or avalanches. The size of these avalanches is distributed according to a power law with an exponent of τ = 1.29(2). The additional observation of finite-size scaling of the avalanche distributions, with an avalanche dimension D = 1.89(3), gives strong indications towards self-organized criticality in this system. Furthermore, we determine exponents governing the roughening dynamics of the flux surface using some universal scaling relations. These exponents are compared to those obtained from a standard roughening analysis.