Floating of the modulation wave in incommensurateRb2ZnCl4

Nuclear-magnetic-resonance measurements in ${\mathrm{Rb}}_2$Zn${\mathrm{Cl}}_4$ show that in the vicinity of the paraelectric-incommensurate transition floating of the phase of the pinned incommensurate modulation wave results in a partial motional averaging of the incommensurate line broadening. The root-mean-square phase fluctuations increase from 20° at $T_I-T=7\mathrm{}$ K to 65° at $T_I-T=0.5\mathrm{}$ K.