Phonon dispersion and solitons in crystalline solids

Although the dispersion relation for phonons propagating in crystalline lattice has been studied for many years, the effect of lattice dispersion on the shape of a propagating pulse has not been studied experimentally. We report 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 been able to detect the formation of acoustic solitons in which the effects of lattice dispersion are balanced by elastic non-linearity. (C) 1999 Elsevier Science B.V. All rights reserved.