Phonon dispersion and solitons in crystalline solids

Although the dispersion relation for phonons propagating in crystalline lat tice has been studied for many years, the effect of lattice dispersion on t he shape of a propagating pulse has not been studied experimentally. We rep ort on an observation of the change in shape of a strain pulse propagating in crystal silicon, and from these measurements estimate the dispersion of long wavelength longitudinal acoustic phonons. In magnesium oxide we have b een able to detect the formation of acoustic solitons in which the effects of lattice dispersion are balanced by elastic non-linearity. (C) 1999 Elsev ier Science B.V. All rights reserved.