AC measurements of edgeless currents in a Corbino ring in the quantum Hall regime

Measurements have been made of radial currents in a two dimensional electron gas in the quantum Hall regime using a Corbino ring geometry. A small solenoid is used to modulate the flux linking a high mobility GaAs-AlxGa1-xAs Corbino ring, thereby inducing an alternating radial current flow. Plateaus of current value are observed giving a clear indication that quantization in this geometry occurs for bulk, opposed to edge, charge transport. We find that the Corbino ring behaves as a quantised a.c. current source over a wide range of loading resistance values and several decades of frequency. The internal impedance of that current source is much larger than the Hall resistance and is dominated by the internal capacitance of the ring. (C) 1997 Elsevier Science Ltd.