Probing the edge of a 2DEG by time-resolved transport measurements

We have studied time-resolved transport in a two-dimensional electron gas in the integer and fractional quantum Hall regime. In samples with a smooth edge and an additional screening electrode, the propagation velocity of high-frequency signals depends on the number and width of the involved edge channels, and thus can be used to obtain an approximate electron density profile. The amplitude of the transmitted signals oscillates with respect to the applied magnetic field with maxima appearing close to integer and fractional bulk filling factors. While the data around filling factor 1/3 are qualitatively similar to those around filling factors 1 and 2, deviations appear around filling factor 2/3. At odd filling factors, signal propagation in partially decoupled edge channels is observed. (C) 1997 Elsevier Science B.V. All rights reserved.