GAPLESS PHASON IN AN ANTIFERROELECTRIC LIQUID-CRYSTAL

The phason dispersion in the antiferroelectric Sm-C(A) liquid crystal line phase of 4-(1-methylheptyl-oxycarbonyl)phenyl 4'-octyloxybiphenyl -4-carboxylate has been studied by quasielastic light-scattering exper iments. The phason is found to be gapless as predicted for a Goldstone mode recovering the broken continuous symmetry. The dispersion has a minimum at q = 2q(c), where q(c) is the wave vector of the unperturbed Sm-C(A) structure. These results are consistent with the alternating -tilt model of the antiferroelectric Sm-C(A) phase.