MAGNETOPLASMA RESONANCES IN 2-DIMENSIONAL ELECTRON-RINGS

Employing millimeter-wave spectroscopy, we have studied the magnetoplasma excitations of a two-dimensional electron gas confined in a ring geometry. The observed spectrum decomposes into several high- and two-low-frequency branches. For large magnetic fields the latter are identified as edge magnetoplasmons localized at the inner and outer; boundary of the rings. With decreasing magnetic field the inner edge mode exhibits a crossover from antidotlike to dotlike behavior. The resonances can also be analyzed in terms of plasmons in a strip with periodic boundary conditions.