Nonlinear dielectric spectroscopy of antiferroelectric liquid crystals in various smectic phases

Nonlinear dielectric spectroscopy in frequency domain has been applied to antiferroelectric liquid crystals in various smectic phases including antiferroelectric SmC*_A, SmC*_F12 and incommensurate SmC*_α phases. We have observed different characteristic third-order nonlinear dielectric spectra ε* 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*_α phases, we have observed the critical behavior of soft mode that condenses in the SmC* _α phase by ε*₃. The obtained nonlinear dielectric spectra are discussed by using phenomenological models for respective relaxation.