Optical demonstration of an electric-field-induced tricritical point in a nematic liquid crystal with negative dielectric anisotropy.

The Landau-de Gennes phenomenological theory predicts the existence of a tricritical point in nematic liquid crystals with negative dielectric anisotropy, at which the nematic-isotropic phase transition changes from first order to second order under a sufficiently strong electric field. In this study, we successfully demonstrated the existence of a tricritical point by measuring the transmitted light intensity near the nematic-isotropic phase boundary under an applied electric field using a polarizing microscope and a temperature-gradient cell that allows position-to-temperature mapping with high accuracy. Furthermore, we measured the response of the transmitted light intensity to a superimposed ac electric field, and discussed the results on the basis of the phenomenology.