Contactless detection of current breakdown of the quantum Hall effect

Abstract

Contactless measurements have been made, using a torque magnetometer, of the size and decay times of the eddy currents induced in a high mobility two-dimensional electron system, as the magnetic field is swept through the magnetoresistance minima associated with the quantum Hall effect. The currents show a highly non-linear dependence on the sweep rate, suggestive of the breakdown of nearly-dissipationless current flow. Comparison of the critical current at which breakdown occurs in our experiments with previously reported values indicates that the majority of the current flows close to the edge of our sample. The observation of a rapid initial decay followed by a much slower one (of the order of hours at the lowest temperatures) upon stopping the field sweep is further evidence that the quantum Hall effect is initially destroyed by the large eddy current; after a short time the current density drops below the critical value and the nearly dissipationless state returns.