Studies on 133Cs NMR spectra and spin-lattice relaxation times in incommensurate Cs2HgCl4

133 Cs NMR spectra and the spin-lattice relaxation times, T 1 , in Cs 2 HgCl 4 crystals were measured in the ranges of 160–361 K and 160–371 K, respectively. The central lines of the spectra show small splittings characteristic of the incommensurate (IC) phase. The splitting increases with decreasing temperature. The critical exponent ζ of T 1 at the phase transition from normal (N) to IC phase was determined to be 0.615±0.025 in the high-temperature side of the transition, which is in good agreement with the three-dimensional X Y model predicting the one-dimensional modulation wave in the IC phase. The frequency dependence of T 1 in the IC phase can be explained by the fluctuations of phason with a small gap, 0–5 MHz, and amplitudon.