Spin-lattice relaxation via floating of the incommensurate modulation wave in Rb2ZnCl4

A high temperature resolution measurement of the 35Cl spin-lattice relaxation rate T-11 in Rb2ZnCl4 close to the paraelectric-incommensurate transition temperature TI is reported. The results can be explained by the recently developed theory of spin-lattice relaxation via large scale fluctuations of the modulation wave in incommensurate systems. At lower temperatures the conventional theory of relaxation via phason and amplitudon fluctuations applies.