Nonlinear self-localized surface waves in a ferroelastic medium

Nonlinear self-localized surface waves in a ferroelastic crystal with stric tion coupling of the order parameter and the lattice deformations are inves tigated. The frequency spectrum of these waves is shown to be located in th e gap between the upper quasioptic and the lower quasiacoustic branches of the harmonic spectrum. A nonlinear Schrodinger equation for the envelope of the surface wave is derived, and its solitonic solutions are obtained. Whe n capillary effects on the surface of the crystal exist, it is found that t he nonlinear surface wave excites the volume waves, thus carrying the energ y into the crystal interior at the frequency of the fundamental wave. Hence , such a wave is a leaky or quasisurface wave. The conditions for the exist ence of the nonlinear surface elastic waves and for their self-localization below the quasiacoustic spectrum branch are also discussed. In contrast to the previous case the nonlinear surface waves are stable and thus not leak y.