Surface acoustic wave studies of quantum nanostructures

Abstract

Surface acoustic wave (SAW) scattering has been used as a contactless probe of the electronic properties of quantum nanostructures. Interdigital transducers, operating at 70 MHz, were deposited on the edges of samples containing large-area arrays of quantum wires and dots. Due to the piezoelectric coupling between the SAWs and the electronic systems, very small changes in the attenuation and velocity of a SAW pulse are measured with magnetic field at low temperatures. With the SAW propagation direction perpendicular to the wires, oscillations were observed due to the magnetic depopulation of 1D sub-bands. Using a simple model, characteristic confinement potentials were calculated at different electron densities. With the SAW propagation direction parallel to the wires, a monotonic decrease in amplitude is seen with increasing electron density. In quantum dots, the transmitted SAW amplitude shows a broad asymmetric minimum as a function of magnetic field, which reflects the density of single-electron energy level crossings per unit magnetic field interval. A simple model, assuming parabolic confinement, predicts a peak in the level crossing density at low magnetic fields, and we observe a corresponding decrease in SAW amplitude.