Observation of “dark” axisymmetric plasma modes in a single disk of two-dimensional electrons

The microwave absorption spectra of a two-dimensional electron system based on GaAs/AlGaAs heterostructures in a perpendicular magnetic field are experimentally investigated. A unique noninvasive technique for the excitation of “dark” axisymmetric plasma oscillations in single disks of two-dimensional electrons is developed. The excitation conditions and physical properties of the new dark plasma modes are studied in detail. The experimental results are in excellent agreement with theoretical calculations.