Observation of Two-Dimensional Plasmons and Electron-Ripplon Scattering in a Sheet of Electrons on Liquid Helium

The two-dimensional plasmon dispersion relation ${{\omega }_p}^2=2\mathrm{}\pi N{e}^2\frac{k}{m}$ has been verified in the classical one-component plasma formed by a sheet of electrons in image-potential-induced surface states on liquid helium. For temperatures below 0.68 K the plasmon damping indicates that the electron mobility is limited by electron-ripplon scattering.