Hydrodynamical theory of magnetoplasma excitations in an antidot system

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Abstract
A linear hydrodynamical theory is developed to study the collective excitations of a two-dimensional electron gas in a normal magnetic field, constrained to move about a circular, infinite potential barrier (known as an antidot). The theory reveals three low-frequency branches in the collective spectrum: (i) a branch that starts from zero at zero magnetic field, reaches a broad maximum at a moderate field, and decreases slowly thereafter; (ii) a mode at the cyclotron resonance frequency; and (iii) a mode that starts at a finite frequency at zero field and merges into the cyclotron resonance at high field. Recent experimental data are compared with the present theoretical results.