Nonlinear Dielectric Spectroscopy of Antiferroelectric Liquid Crystals in Various Smectic Phases

摘要

Nonlinear dielectric spectroscopy in frequency domain has been applied to antifer-roelectric liquid crystals in various smectic phases including antiferroelectric SmC_A~*, SmC_(F12)~* and incommensurate SmC_(alpha)~* phases. We have observed different characteristic third-order nonlinear dielectric spectra epsilon_3~* in respective phases. In SmC_A~* and SmC_(F12)~* phases, nonlinear dielectric response originated from Goldstone-like fluctuation with long relaxation time along the helical structure have been observed, which cannot be usually observed in linear spectrum. In the SmC_(alpha)~* phases, we have observed the critical behavior of soft mode that condenses in the SmC_(alpha)~* phase by epsilon_3~*. The obtained nonlinear dielectric spectra are discussed by using phenomenological models for respective relaxation.