HIGH-PRESSURE BRILLOUIN STUDY OF INCOMMENSURATE RUBIDIUM ZINC-CHLORIDE

The pressure dependence of the longitudinal acoustic modes, correspond ing to the elastic constants C22 and C33, and the transverse acoustic modes, corresponding to the elastic constants C44 and C66, of Rb2ZnCl4 have been studied using Brillouin scattering. The normal (N) to incom mensurate (IC) transition is reflected in the pressure dependence of t he C22 and C44 modes. We find that the step in the temperature depende nce of the C66 mode at the N-IC transition increases with increasing p ressure, indicating a stronger coupling of the corresponding strain to other excitations in the material.