Elastic scattering and absorption of surface acoustic waves by a quantum dot

Abstract

We study theoretically the piezoelectric interaction of a surface acoustic wave (SAW) with a two-dimensional electron gas confined to an isolated quantum dot. The electron motion in the dot is diffusive. The electron-electron interaction is accounted for by solving the screening problem in real space. Since the screening in GaAs/AlGaAs heterostructures is strong, an approximate inversion of the dielectric function epsilon(r,r') can be utilized, providing a comprehensive qualitative picture of the screened SAW potential and the charge redistribution in the dot. We calculate the absorption and the scattering cross-sections for SAW's as a function of the area of the dot, A, the sound wave vector, q, and the diffusion coefficient D of the electrons. Approximate analytical expressions for the cross-sections are derived for all cases where the quantities A*q^2 and A*omega/D are much larger or smaller than unity; omega is the SAW frequency. Numerical results which include the intermediate regimes and show the sample-specific dependence of the cross-sections on the angles of incidence and scattering of surface phonons are discussed. The weak localization corrections to the cross-sections are found and discussed as a function of a weak magnetic field, the frequency, and the temperature. Due to the absence of current-carrying contacts, the phase coherence of the electron motion, and in turn the quantum corrections, increase as the size of the dot shrinks. This shows that scattering and absorption of sound as noninvasive probes may be advantageous in comparison to transport experiments for the investigation of very small electronic systems.