Lost surface waves in nonpiezoelectric solids
AbstractThe existence of shear surface acoustic waves (SAWs) has been regarded as impossible in nonpiezoelectrics with homogeneous flat surfaces. We show that transverse shear SAWs can propagate near the flat surfaces of all crystalline dielectrics due to the omnipresent flexoelectric coupling. It appears that the penetration depth of the previously unexplored SAW is defined by the flexocoupling strength. Since the SAW occurs due to the flexoelectric coupling, we name it the flexoelectric SAW (flexo-SAW). We predict that the phonon spectra corresponding to the flexo-SAWs and bulk phonon modes can be separated in thin nonpiezoelectric films, such as strontium titanate.