Surface acoustic waves on GaAs/<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">Al</mml:mi></mml:mrow><mml:mrow><mml:mi mathvariant="normal">x</mml:mi></mml:mrow></mml:msub></mml:mrow></mml:math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">Ga</mml:mi></mml:mrow><mml:mrow><mml:mn>1</mml:mn><mml:mi mathvariant="normal">−</mml:mi><mml:mi mathvariant="normal">x</mml:mi></mml:mrow></mml:msub></mml:mrow></mml:math>As heterostructures

The interaction between surface acoustic waves and quasi-two-dimensional inversion electron systems on GaAs/${\mathrm{Al}}_{\mathrm{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$As heterojunctions is investigated in high magnetic fields and at low temperatures. The interaction of the surface acoustic wave with high-mobility inversion electrons leads to strong quantum oscillations in both the transmitted surface wave intensity as well as in the sound velocity, reflecting the quantum oscillations of the magnetoconductivity as a function of an applied magnetic field. We study the dependence of this interaction on the magnetic field and on the surface-acoustic-wave power and frequency, and discuss the results using simple models. The influence of slight spatial inhomogeneities in the carrier density on the line shape of the quantum oscillations is analyzed in detail and related to their influence on the quantum Hall effect. First experimental results on the interaction of surface acoustic waves with two-dimensional electron systems in gated heterojunctions providing an adjustable carrier density are presented.