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Abstract
Nonlinear dielectric spectroscopy in frequency domain has been applied to antiferroelectric liquid crystals in various smectic phases including antiferroelectric SmC A *, SmC FI2 * and incommensurate SmCα* phases. We have observed different characteristic third-order nonlinear dielectric spectra ϵη3* in respective phases. In SmC A * and SmC FI2 * 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 SmCα* phases, we have observed the critical behavior of soft mode that condenses in the SmCα* phase by ϵ3*. The obtained nonlinear dielectric spectra are discussed by using phenomenological models for respective relaxation.