Abstract
The dynamics of the incommensurate (IC) modulation is investigated for several one-dimensionally incommensurately modulated crystals near the transition to the normal high temperature phase at the temperature T i by means of quadrupolar perturbed nuclear magnetic resonance (NMR) spectra and nuclear spin-lattice relaxation. All results can be described consistently in terms of a static modulation in the IC phase without any indication for ‘floating’ or large scale fluctuations of the modulation wave. The critical exponents derived from the NMR line shape and the relaxation times T 1 very nicely fit to the universality class of the 3d-XY model. For Rb2ZnBr4 and Rb2ZnCl4 crystals the characteristic frequency of the critical dynamics of the order parameter (OP) slows down below the Larmor frequency used in the 87Rb NMR relaxation time measurements. In this particular case one can derive the characteristic frequency of the critical dynamics of the OP above T i and of the phason below T i from the Larmor frequency dependence of T 1.
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