Novel breakdown of the quantum Hall effect: An example of self-organised criticality?

We observe a novel breakdown of the quantum Hall effect in a two-dimensional electron gas using a contact-free method in which circulating eddy currents are induced upon sweeping the magnetic field, and are detected via their magnetic moment. The currents are largest around integer filling factor, where the longitudinal resistivity $\rho_{xx} \rightarrow 0$. Below about 1$\un{K}$, a strong “noisy” behaviour of the induced current is seen around filling factor $\nu=2$. We interpret this using a model in which the circulating current is accompanied by a radial Hall electric field and consequent charge build up near the sample edge. Breakdown occurs at random “weak points” in the sample when the Hall field reaches a critical value, causing an “avalanche” of charge to be re-distributed to the bulk. The frequency distribution of the low-temperature noise jumps follows a power law, consistent with self-organised criticality.