ELECTRON-PHONON INTERACTION IN THE QUANTUM HALL-EFFECT REGIME

The absorption of ballistic phonons with frequencies in the 100-GHz ra nge by a two-dimensional electron gas (2DEG) has been studied in a qua ntizing magnetic field. The 2DEG was formed at the interface of a GaAs /AlxGa1-x As heterojunction. Acoustic phonons were created by heating the substrate locally with a focused laser beam. The phonons traveled ballistically through the crystal and were partially absorbed by the 2 DEG. This led to a transfer of momentum into the 2DEG (phonon-drag eff ect) resulting in phonon-induced voltages and currents. These quantiti es gave detailed information about the interaction between acoustic ph onons and the 2DEG as a function of both the incident angle of the abs orbed phonons and the magnetic field. We observed that the dependence of the phonon-drag signal on the angles of incidence was neither affec ted by the magnetic field nor by the phonon spectrum. The absolute int ensity of the phonon-drag signal, however, oscillated in phase with th e Shubnikov-de Haas oscillations. These results could be explained wit h a simple microscopic theory of the electron-phonon interaction toget her with a macroscopic model for the response of the 2DEG on the absor ption of ballistic phonons.