Electrical tuning of Bragg diffraction in polar heliconics

Recently discovered ferroelectric nematic (FN) liquid crystals (LCs) exhibit spontaneous polarization, challenging the common belief that dipole interactions in liquids are too weak and thermal fluctuations are too strong to sustain the long-range ordering of electric dipole moments [X. Chen et al., Proc. Natl. Acad. Sci. U.S.A. 117, 14021–14031 (2020)]. The peculiar combination of fluidity and polarity characterizing these materials is opening the way to a whole world of new phenomena and phases. Among them, a polar version of the heliconical cholesteric phase observed recently [J. Karcz et al., Science 384, 1096 (2024)]. This phase is spontaneously formed by the intrinsic electric dipole interactions inducing a heliconical orientation of the polar director and does not require an external field or special conditions for elastic constants for its stabilization. The polar heliconical structure is ideal for designing tunable optical elements that operate at low-amplitude electric fields and require only a single wavelength-switching element for device fabrication. In this work we present an extensive characterization of the polar heliconical phase using techniques established for non-polar heliconics and investigate the electrical tuning of Bragg diffraction at both normal and oblique incidence of light.