The temperature variation of the phase soliton density has been determined in ${\mathrm{Rb}}_2$Zn${\mathrm{Cl}}_4$ and a nonclassical critical exponent ½ has been found. Electron-paramagnetic-resonance and nuclear-magnetic-resonance data demonstrate that in ${\mathrm{K}}_2$Se${\mathrm{O}}_4$, ${\mathrm{Rb}}_2$Zn${\mathrm{Cl}}_4$, and ${\mathrm{Rb}}_2$Zn${\mathrm{Br}}_4$ the soliton width is large as compared to the intersoliton spacing over most of the incommensurate phase so that the continuum description is adequate.

• Received 15 September 1980

DOI:https://doi.org/10.1103/PhysRevLett.46.1406