Statics and dynamics of the modulation in incommensurate Rb2ZnBr4 as detected by NMR

The dynamics of the incommensurate modulation of Rb₂ZnBr₄ is investigated near the transition to the normal high-temperature phase using first-order quadrupole effects in nuclear magnetic resonance (NMR).⁸⁷Rb NMR spectra and two-dimensional⁸⁷Rb NMR exchange spectra are reported. All results can be described consistently in terms of a static modulation in the incommensurate phase without any indication for “floating” or large-scale fluctuations of the modulation wave. The spectra taken about 135 K below T_i in the lower incommensurate phase well above the soliton regime show no indication for the existence of a higher-order commensurate modulation in Rb₂ZnBr₄.