Magnetoplasmons in a ring-shaped two-dimensional electron gas

The collective excitations (plasmons) of a ring-shaped two-dimensional electron gas under a perpendicular magnetic field are studied. The hydrodynamical theory reveals that for each value of the excitation angular momentum, the spectrum can be characterized as a set of high-frequency bulk magnetoplasmons (with some of them displaying, however, an anomalous negative magnetodispersion) and two low-frequency edge magnetoplasmons circulating along the inner and outer ring boundaries, in opposite directions. Excellent quantitative agreement is obtained with all the available experimental data. {} 1996 The American Physical Society.