Order parameter dynamics in the plane wave and soliton limit of the IC phase of Rb2ZnCl4

Refining previous calculations of the critical contribution to the nuclear spin-lattice relaxation time T-1 it is shown for the slow-motion limit that the critical exponent of T-1 vanishes and that the exponent describing its frequency dependence deviates from the value 0.5 which so far has been assumed to hold. Corresponding measurements in the plane wave limit of the incommensurate (IC) phase of Rb2ZnCl4 for which the slow-motion condition is known to be fulfilled for the "phason" excitation confirm this result. In the low-temperature part of the IC phase the temperature dependence of T-1 of the upper-frequency satellite transition of Rb-87 was measured not only at the edge singularities of the frequency distribution but also at the appearing "C lines". It is shown that on approaching the transition to the subsequent commensurate (C) phase T-1 for nuclei in the phase solitons decreases while it increases for the the nuclei in the C regions. Thus, earlier theoretical results concerning the different dynamical behaviour of nuclei located within or outside the solitons are experimentally fully confirmed.