X-ray scattering in the normal and incommensurate phases of Rb2ZnCl4

Abstract

The static critical behaviour at the normal to incommensurate phase transition in Rb₂ZnCl₄ has been investigated by means of diffuse X-ray scattering. The measured values of the critical exponents gamma and nu are in good agreement with theoretical estimates for the d=3XY model. Measurements of the diffuse scattering in the incommensurate phase just below T_c are consistent with those expected if there are nearly gapless phase excitations. At lower temperatures an asymmetry develops in the predominantly acoustic mode scattering emanating from the primary satellite reflections which is attributed to coupling of acoustic and phason modes. The temperature dependence of the intensity of several higher-order satellites has been measured at temperatures just above the lock-in transition but is not understood.