MOLECULAR FLUCTUATIONS IN SMECTIC PHASES POSSESSING ANTIFERROELECTRICORDERING

In order to investigate molecular fluctuation in chiral smectic phases that possess antiferroelectric ordering, we have carried out electroo ptic measurements of linear and second harmonic responses in 4-(1-meth ylheptyloxycarbonyl)phenyl 4'-octyloxybiphenyl-4-carboxylate (MHPOBC) which has two antiferroelectric smectic phases, namely, smectic C-alph a (SmCalpha*) and smectic C-A* (SmCA*). In the SmCA* phase, we confir med the relaxation of the antiferroelectric phase mode corresponding t o the symmetry-recovering Goldstone mode in the frequency dispersion o f optical responses under a sinusoidal electric field. However, no evi dence of the antiferroelectric phase mode was found in the SmCalpha p hase, although we recognized the relaxation corresponding to the ferro electric phase mode. In addition, we speculate on the fluctuation mode ls responsible for the electrooptic behavior in the SmCalpha and SmCA phases.