New Class of Magnetoresistance Oscillations: Interaction of a Two-Dimensional Electron Gas with Leaky Interface Phonons

We report on a new class of magnetoresistance oscillations observed in a high-mobility two-dimensional electron gas (2DEG) in GaAs-AlₓGa_1-xAs heterostructures. Appearing in a weak magnetic field ( B<0.3T) and only in a narrow temperature range ( 2K<T<9K), these oscillations are periodic in $1/B$ with a frequency proportional to the electron Fermi wave vector, kF. We interpret the effect as a magnetophonon resonance of the 2DEG with leaky interface-acoustic phonon modes carrying a wave vector q0ex0ex=0ex0ex2kF. Calculations show a few branches of such modes existing on the GaAs-AlₓGa_1-xAs interface, and their velocities are in quantitative agreement with the observation.