Ferroelectricity in the Lyotropic Cholesteric Phase of Poly L-Glutamate

Relatively strong second-harmonic generation (SHG) was observed in the lyotropic cholesteric phase of the poly(γ-benzyl-L-glutamate-co-γ-methyl L-glutamate) (PBMLG) in benzyl alcohol (BA) with application of an electric field. Using an SHG interferometry technique, we confirmed that the phase of SHG was reversed by reversing the electric field, clearly indicating the switching of nonlinear polarization. By applying a triangular wave voltage, a switching current peak was observed, indicating the existence of spontaneous polarization. Based on these experimental results, we safely concluded that the cholesteric phase of the PBMLG-BA lyotropic system is in fact a ferroelectric cholesteric phase, where a polar plane rotates along the helical axis. This is the first proper ferroelectricity in liqiud crystals.