Constant molecular rotation at the smectic-Ato smectic-C*transition in ferroelectric liquid crystals

We present dielectric measurements extended over the frequency range from ${10}^6$ to ${10}^9$ Hz on a pure ferroelectric liquid crystal. In clear contrast to the generally attributed origin of the ferroelectricity in liquid crystals arising from a slowing down of the molecular rotation around the long molecular axis, we find by direct observation the corresponding dielectric relaxation unchanged at the smectic-A to smectic-${\mathit{C}}^{\mathrm{*}}$ transition. This result requires a new interpretation of a recently published degenerate four-wave-mixing experiment by Lalanne et al. [Phys. Rev. Lett. 62, 3046 (1989)].