Edge magnetoplasma excitations in a two-dimensional electron system with strong screening

The dispersion of plasma and magnetoplasma excitations in two-dimensional electron systems with a closely spaced back gate is experimentally investigated using optical detection of microwave absorption. In disk samples, both cyclotron and edge screened magnetoplasmons are observed. It is established that the magneticfield behavior of both modes is in good agreement with the existing theory describing the dispersion of screened magnetoplasma excitations. It is shown that, in a strong magnetic field, the dispersion of screened magnetoplasma excitations is quadratic. This makes it possible to associate magnetoplasma waves with a quasiparticle with a mass, which possesses a number of unique properties.