Attenuation of surface acoustic waves by quantum dots

The attenuation Γ of surface acoustic waves (SAWs) by an array of quantum dots is considered. The processes contributing to Γ, direct and intralevel (Debye) absorption and (elastic) scattering off the direction of the SAW are discussed for two limiting cases of the energy spectra of the dots: firstly a continuous spectrum, which is realized when the SAW frequency ω is much larger than the mean level spacing Δ or when the broadening of the levels is sufficiently strong, Δ < τ_φ^-1, τ_φ^-1 being the phase breaking rate; secondly a discrete spectrum, obtained for ω, τ_φ^-1 < Δ. The results show that the sensitivity of Γ to weak-localization effects such as magnetic fields, spin-orbit scattering and temperature, are considerably enhanced for a discrete spectrum. It is argued that the non-invasive character of the measurement of Γ makes the SAW experiments especially suitable for the determination of the temperature dependence of τ_φ^-1 and the equilibration rate of the electronically isolated dots.