87Rb Spin-Lattice Relaxation in the Incommensurable Phase of Rb2ZnCl4

The contribution of phason and amplitudon excitations to the spin-lattice relaxation rate in structurally incommensurable (I) systems as well as the NMR line shapes in these systems have been evaluated and compared with the ⁸⁷Rb NMR data for Rb₂ZnCl₄. The presence of a strong, temperature-independent relaxation mechanism, which disappears below the "lockin" transition, demonstrates that in the I phase of Rb₂ZnCl₄ the spin-lattice relaxation rate is dominated by phasons.