High pressure Brillouin study of incommensurate rubidium zinc chloride

Abstract The pressure dependence of the longitudinal acoustic modes, corresponding to the elastic constants C 22 and C 33 , and the transverse acoustic modes, corresponding to the elastic constants C 44 and C 66 , of Rb 2 ZnCl 4 have been studied using Brillouin scattering. The normal (N) to incommensurate (IC) transition is reflected in the pressure dependence of the C 22 and C 44 modes. We find that the step in the temperature dependence of the C 66 mode at the N-IC transition increases with increasing pressure, indicating a stronger coupling of the corresponding strain to other excitations in the material.