Electrooptic Observation of the Goldstone and Soft Modes near the SmA-SmC_A^* Phase Transition

In order to investigate the details of the molecular fluctuation behavior around the SmA-SmC_A^* phase transition point, we have carried out electrooptic measurements in 4-(1-trifluoromethvlheptyloxy-carbonyl) phenyl-4\u27-octyloxybiphenyl-4-carboxylate, which undergoes a phase transition directly from SmA to SmC_A^*, as functions of temperature and frequency. The relaxation due to the Goldstone mode was clearly observed in the SmC_A^* phase. We found that the optical signal due to the Goldstone mode vanishes at a certain temperature in the antiferroelectric SmC_A^* phase. The helix distortion due to the antiferroelectric Goldstone mode excited by an electric field is discussed