A 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-Al$_x$Ga$_{1-x}$As heterostructures. Appearing in a weak magnetic field ($B<$ 0.3 T) and only in a narrow temperature range (2 K $<T<$ 9 K), these oscillations are periodic in 1/B with a frequency proportional to the electron Fermi wave vector, $k_F$. We interpret the effect as a magnetophonon resonance of the 2DEG with leaky interface-acoustic phonon modes carrying a wave vector $q=2k_F$. Calculations show a few branches of such modes on the GaAs-Al$_x$Ga$_{1-x}$As interface, and their velocities are in quantitative agreement with the data.