The electric admittance of a two-dimensional electron gas on liquid helium measured at audio frequencies ω is observed to oscillate as a function of magnetic field at strong magnetic fields. The oscillations can be attributed to the propagation of very-low-frequency (ωτ∼${10}^{\mathrm{-}6}$, τ scattering time; ω/${\mathrm{\omega }}_{\mathit{c}}$∼${10}^{\mathrm{-}8}$, ${\mathrm{\omega }}_{\mathit{c}}$ cyclotron frequency) edge magnetoplasmons. The directly determined dispersion relation agrees with theory and quantitatively with measurements in the collisionless regime (ωτ≫1). The attenuation, theoretically obtained by incorporating the screening in a simple local-capacitance model, agrees well with experiments.

• Received 12 July 1991

DOI:https://doi.org/10.1103/PhysRevLett.67.2199