Acoustic-phonon propagation in superlattices

Abstract

Bragg reflection of acoustic phonons propagating through a periodic superlattice is explored in detail. We examine Bragg reflection for a single vibrational mode and relate it to gaps, or stop bands, in the phonon dispersion relation at the center and boundary of the folded Brillouin zone. Bragg reflection due to the coupling of different polarization modes is similarly linked to intrazone stop bands. We also calculate phonon transmission rates, and explore in depth the spatial distribution of the transmitted phonon intensity. These results are compared with experimental phonon images that provide a two-dimensional map of the acoustic-phonon transmission as a function of propagation direction.