Phase Transition and Collective Fluctuation of a Confined Antiferroelectric Liquid Crystal: Dielectric Spectroscopy of the Frustrated Ferroelectric Smectic-C^* Phase

The dielectric and switching behaviors have been investigated using cells of varying thickness of an antiferroelectric liquid crystal, (S)-4-(1-methylheptyloxycarbonyl) phenyl 4'-octylbiphenyl-4-carboxylate (S-MHPBC) which shows antiferroelectric and ferrielectric subphases, designated as the AF and Sm-C_γ^* phases, respectively, in a temperature region above the Sm-C_A^* phase. While the tristable switching with a characteristic dc threshold and hysteresis is clearly observed in the AF phase in a cell thicker than about 8 µm with homogeneous alignment, a thresholdless bistable switching is confirmed in a cell thinner than 3.9 µm. The emergence of thresholdless bistable switching means that confinement of the antiferroelectric liquid crystal to the thin cell induces the phase transformation from the AF and Sm-C_γ^* phases to the frustrated ferroelectric Sm-C^* phase. In addition, a novel dielectric relaxation appears in the temperature region of the AF and Sm-C_γ^* phases in the liquid crystal confined to a cell 3.9 µm thick. We concluded that the novel dielectric relaxation appearing in the confined antiferroelectric liquid crystal is associated with a Goldstone mode of the frustrated ferroelectric Sm-C^* phase transformed from the AF and Sm-C_γ^* phases.