NQR study of dynamics in incommensurate phases

Dynamic processes in solids exhibiting structurally incommensurate phases a re briefly reviewed, and the application of NMR and NQR is discussed. The u nique utility of these methods, - arising due to, on one hand, the microsco pic resonant nature of the probe used and, on the other, the presence of pe riodic, though incommensurable, structure -, is brought out by presenting r ecent results in a prototype system (Rb2ZnCl4) in the presence of randomly quenched disorder. In particular, the interesting new methodology of measur ing, by analysing NQR spin echo modulation, ultra-slow diffusion like colle ctive motions of ensembles of atoms in the presence of pinning effects due to disorder is illustrated with new results.