Nonlinear dielectric response of antiferroelectric liquid crystals in the smectic C alpha* phase.

Nonlinear dielectric response of antiferroelectric liquid crystals has been studied in the smectic C(alpha)* (SmC(alpha)*) phase. The linear dielectric spectrum shows a single relaxation of Debye type and its relaxation frequency is as high as one hundred kHz. The profile of the third-order nonlinear dielectric spectrum varies in complex fashion with temperature. In the vicinity of the SmA-SmC(alpha)* phase transition, experimentally obtained nonlinear spectra are well described by those calculated with phenomenological theory of Landau type. The soft mode of the SmC(alpha)* phase shows critical slowing-down near the transition temperature. In the lower-temperature region of the SmC(alpha)* phase, the contribution from the soft mode of the SmC(alpha)* phase reduces and the other relaxation mode with Debye-type spectrum appears at several hundred Hz in the nonlinear spectrum. The appearance of this low-frequency mode suggests that the cooperative fluctuation of directors over long range exists in the SmC(alpha)* phase.