Wide temperature range tunable selective reflection of light by chiral ferroelectric nematic phase

A chiral mixture composed of ferroelectric nematic mesogen and chiral additives shows a right-angle chiral nematic (N*) followed by a chiral ferroelectric nematic (N_F*) at lower temperatures  [1–3]. The N_F* phase is a recently realized new chiral nematic with a polar helical order.  We explore both the N* and N_F* phases in three chiral mixtures containing ferroelectric nematic mesogen  RM734 doped with different chiral additives. In all three chiral mixtures, the helical pitch measured in a Cano wedge cell shows a strong temperature dependence. In one chiral mixture, the pitch decreases monotonously in both the N* and N_F* phases with a temperature decrease. However, in the other two mixtures, the pitch shows a non-monotonous trend with a decrease of temperature; pitch decreases in the N* phase while increases in N_F* phase. The selective Bragg reflection of light from the N_F* cell with hybrid surface alignment shows a continuous redshift by 200 nm driven by a temperature decrease.