Generalization of Meyer’s ferroelectricity to cholesteric phase : electroclinic coupling and prediction of a new ferrocholesteric phase

We present a generalization of Meyer's theory of the trilinear coupling between the smectic layers, the tilt angle of the optical axis with respect to the layer normal and the electric polarization which accounts for the spontaneous ferroelectricity in smectic C* liquid crystals. This coupling allows for the description of the electroclinic effect, I-ethe appearance of a polarization and a tilt angle induced by an extemal electric field in smectic C*, smectic A and N* (cholesteric) phases. A new « ferrocholesteric » phase is expected between C* and N* phases when the local order is smectic C*-like with a small but non-zero polarization. Eventually, a comparison is made with experimental data available in N* phase.