Dielectric relaxation modes in the antiferroelectric smectic CA* phase

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Abstract
We have studied the dielectric behavior in the antiferroelectric SmCA* phase of 4-(1-methyl-heptyloxycarbonyl)phenyl 4'-octyloxybiphenyl-4-carboxylate (MHPOBC). Two dielectric relaxations were recognized without a dc field in SmCA*. The lower-frequency relaxation is attributed to the rotation around the short axis of molecules, and the higher-frequency one is due to the distortion of the antiferroelectric ordering; the opposite rotation of molecules in adjacent layers. In addition, the helical distortion due to the dielectric anisotropy was observed in optical responses as well as in conoscopic figures. The relaxation frequency of the collective helical fluctuation was measured by means of electro-optic measurements. Moreover, we found the dielectric relaxation of the collective helical fluctuation under the application of a dc bias field.