Surface effect on the soft acoustic mode of KD3(SeO3)2studied by microprobed Brillouin scattering

Abstract

Abstract By the use of a microprobed Brillouin scattering system, thermally excited acoustic modes in a ferroelastic KD3(SeO3)2 crystal have been observed as a function of depth from the surface. Both a longitudinal mode c22 and a transverse soft mode c44 propagating along the [010] direction become hard as the observation area closes to the (110) surface just above the transition temperature. Especially, the transition temperature at the surface, determined as the minimum position of the frequency shift of the soft acoustic c44 mode, shifts to lower side by about 0.1 K. It is concluded that the soft acoustic mode associated with the bulk ferroelastic phase transition is modified near the surface. On the other hand, these modes do not show any drastic anomaly near the (001) surface. A configuration effect is suggested between the surface and the propagation direction of the acoustic modes.