Quantum Oscillations in the Surface-Acoustic-Wave Attenuation Caused by a Two-Dimensional Electron System

The interaction of surface acoustic waves with a two-dimensional electron system is investigated on $\frac{\mathrm{GaAs}}{{\mathrm{Ga}}_{1\ensuremath{-}x}{\mathrm{Al}}_{x}\mathrm{As}}$ heterojunctions at low temperatures ($T<~4.2 \mathrm{K}$) and high magnetic fields (\ensuremath{\le} 10 T). Surface acoustic waves are propagated through the heterojunction containing a high-mobility two-dimensional electron gas and situated between the emitting and receiving transducers. The interaction between the two-dimensional electron system and the surface acoustic wave produces strong quantum oscillations in the sound attenuation and the sound velocity which can be quantitatively explained.