Studies on ¹³³Cs NMR Spectra and Spin-Lattice Relaxation Times in Incommensurate Cs₂HgCl₄

Abstract

¹³³Cs NMR spectra and the spin-lattice relaxation times, T₁, in Cs₂HgCl₄ 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 T₁ 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 XY model predicting the one-dimensional modulation wave in the IC phase. The frequency dependence of T₁ in the IC phase can be explained by the fluctuations of phason with a small gap, 0--5 MHz, and amplitudon.