Antiferroelectricity and Chiral Order in New Liquid Crystals of Nonchiral Molecules Studied by Optical Second Harmonic Generation

Abstract

Several homologs of new liquid crystals of strongly bent, achiral molecules have been investigated by optical second harmonic generation. It is shown that the initial nonpolar mesophase is converted into a polar state, which leads to frequency doubling of optical waves by applying electric fields of a few $\mathrm{V}/\ensuremath{\mu}\mathrm{m}$. The observed symmetry breaking is explained by a field-induced antiferroelectric to ferroelectric transition. The symmetry group and nonlinear coefficients as large as ${d}_{31}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}16\mathrm{pm}/\mathrm{V}$ have been determined for the field-induced state from polarization and angle-dependent measurements.