Spectroscopy of a two-dimensional electron gas in the quantum-Hall-effect regime by use of low-frequency edge magnetoplasmons

We have shown that some features of the edge magnetoplasmon (EMP) spectrum in a GaAs/${\mathrm{Al}}_{\mathit{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As two-dimensional electron gas (2DEG) result from the existence of spatially separated edge channels. In radio frequency experiments, transmission resonances attributed to EMP’s in the 2DEG have been measured in the quantum-Hall-effect regime for filling factor values ν=1,2,3,4. For ν=3,4 the linear dependence of plasmon frequency on filling factor is violated. A simple phenomenological model is also presented which treats the EMP’s as interacting charge-density waves propagating along the edge channels. By using the measured plasmon frequencies in this model, information is obtained about the spatial distribution of the edge channels. We are also able to predict the frequencies of new types of edge excitations, referred to as nonequilibrium EMP’s.