Molecular Fluctuations in Smectic Phases Possessing Antiferroelectric Ordering

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Abstract
In order to investigate molecular fluctuation in chiral smectic phases that possess antiferroelectric ordering, we have carried out electrooptic measurements of linear and second harmonic responses in 4-(1-methylheptyloxy-carbonyl)phenyl 4′-octyloxybiphenyl-4-carboxylate (MHPOBC) which has two antiferroelectric smectic phases, namely, smectic Cα * ( SmCα *) and smectic C A * ( SmC A *). In the SmC A * phase, we confirmed the relaxation of the antiferroelectric phase mode corresponding to the symmetry-recovering Goldstone mode in the frequency dispersion of optical responses under a sinusoidal electric field. However, no evidence of the antiferroelectric phase mode was found in the SmCα * phase, although we recognized the relaxation corresponding to the ferroelectric phase mode. In addition, we speculate on the fluctuation models responsible for the electrooptic behavior in the SmCα * and SmC A * phases.