Nonlinear Dielectric Relaxation Spectroscopy of Antiferroelectric Liquid Crystals

Abstract

The relaxation spectra of the linear and nonlinear dielectric constants of the antiferroelectric liquid crystals have been studied in their SmA, SmC* and SmC_A* phases. In the SmA phase near the boundary to the SmC* or SmC_A* phase, both the dielectric constants show a critical behavior due to the softening of the ferroelectric soft mode. In the SmC* phase, we obtain the third-order nonlinear spectrum of a higher-order Debye type with a negative increment, which corresponds to the ferroelectric Goldstone mode observed also in the linear spectrum. In the SmC_A* phase, the antiferroelectric Goldstone mode is observed not in the linear spectrum, but in the third-order spectrum as a Debye-type relaxation with a positive increment. All these spectra can be analyzed in terms of simple phenomenological models.