We report studies of the surface plasmon modes of a layer of electron gas that is embedded in a wider, effective positive background, provided by a parabolic ${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As well. Although conditions in the interior of the electron gas are nearly identical to those in a neutral jellium slab, the more abrupt electronic surfaces in the parabolic well produce a qualitatively different surface plasmon spectrum.

• Received 11 May 1992

DOI:https://doi.org/10.1103/PhysRevB.46.7284