Plasmon and magnetoplasmon excitation in two-dimensional electron space-charge layers on GaAs

Abstract

The excitation of two-dimensional (2D) plasmons in ${\mathrm{Al}}_{\mathrm{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$As-GaAs heterostructures has been investigated with far-infrared transmission spectroscopy. Grating couplers of high efficiency and samples of high mobility (\ensuremath{\mu}\ensuremath{\approxeq}1.8\ifmmode\times\else\texttimes\fi{}${10}^{5}$ ${\mathrm{cm}}^{2}$/V? make it possible to study the 2D plasmon dispersion up to plasmon wave vectors q\ensuremath{\gtrsim}2\ifmmode\times\else\texttimes\fi{}${10}^{5}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$. Thus we can test the theoretically predicted second-order q corrections to the dispersion due to nonlocal effects, finite thickness of the space-charge layer, and correlations. In perpendicular magnetic fields, a strong nonlocal interaction of the 2D magnetoplasmon resonance with harmonics of the cyclotron resonance n${\ensuremath{\omega}}_{c}$ (n=2,3,4,. . .) is observed. Excellent agreement is found with predictions of a classical nonlocal theory.