Anisotropic interface motion of 4He crystal induced by acoustic waves

Interface motions of 4He crystals induced by acoustic waves were investigated in various surface orientations. Inversion of a direction of the force on the interface was observed in the case of acoustic wave from the crystal side above a particular temperature Ti. Ti was about 0.8 K in rough surface and decreased to 0.6 K with approaching the c-facet. These observations were qualitatively explained assuming that the interface motion was induced by acoustic radiation pressure. Relaxation of the interface after stopping the acoustic wave was observed by a high-speed video camera.