A ferroelectric nematic liquid crystal is formed by achiral molecules with large dipole moments. Its orientational order is universally described as unidirectionally polar, which raises the question of how the structure avoids a strong depolarization field and splay deformations that bring about bound charges. We demonstrate a rich plethora of polarization patterns in ferroelectric nematics not constrained by crystallographic axes. Domain walls take on the shapes of conic sections, separating circular vortices of polarization [1,2]
When a flat ferroelectric nematic slab is anchored only at one bounding plate, its ground state becomes optically active, with left- and right-hand twists of polarization; the twists occur in chemically achiral system [3]. Despite the increase in elastic energy of deformations and domain walls, the twists reduce the electrostatic energy and weaken when the material is doped with ions [4].
An external electric field applied to create a splay produces structures in which the splay of one polarity is compensated by a splay of opposite polarity, thus solving the electrostatic problem by geometrical means [5]. Finally, a uniform pattern of electric polarization can be created by applying the electric field to the nematic [6] or isotropic [7] phase of the ferroelectric nematic material. The induced order causes a strong birefringence that can be switched on and off within 100 ns; the effect is promising for electro-optical applications.
This work was supported by NSF grant DMR-2341830.
References:
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[2]        P. Kumari, O. Kurochkin, V. G. Nazarenko, O. D. Lavrentovich, D. Golovaty, and P. Sternberg, Physical Review Research 6, 043207 (2024).
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[7]        K. Thapa, S. Paladugu, and O. D. Lavrentovich, Adv Opt Mater, accepted (2025).