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Abstract Electric field-induced splay of molecular orientation, called the Fréedericksz transition, is a fundamental electro-optic phenomenon in nonpolar nematic liquid crystals. In a ferroelectric nematic N_Fwith a spontaneous electric polarization$${{\bf{P}}}$$ $P$, the splay is suppressed since it produces bound electric charges. Here, we demonstrate that an alternating current (ac) electric field causes three patterns of N_Fpolarization. At low voltages,$${{\bf{P}}}$$ $P$oscillates around the field-free orientation with no stationary deformations. As the voltage increases, the polarization acquires stationary distortions, first splay and twist in a stripe pattern and then splay and bend in a square lattice of +1 and -1 defects. In all patterns,$${{\bf{P}}}$$ $P$oscillates around the stationary orientations. The stationary bound charge is reduced by a geometrical “splay cancellation” mechanism that does not require free ions: the charge created by splay in one plane is reduced by splay of an opposite sign in the orthogonal plane. 

Nematic liquid crystals exhibit nanosecond electro-optic response to an applied electric field which modifies the degree of orientational order without realigning the molecular orientation. However, this nanosecond electrically modified order parameter (NEMOP) effect requires high driving fields, on the order of 10⁸V/m for a modest birefringence change of 0.01. In this work, we demonstrate that a nematic phase of the recently discovered ferroelectric nematic materials exhibits a robust and fast electro-optic response. Namely, a relatively weak field of 2 × 10⁷V/m changes the birefringence by ≈ 0.04 with field-on and-off times around 1 μs. This microsecond electrically modified order parameter (MEMOP) effect shows a greatly improved figure of merit when compared to other electro-optical switching modes in liquid crystals, including the conventional Frederiks effect, and has a potential for applications in fast electro-optical devices such as phase modulators, optical shutters, displays, and beam steerers. 

Abstract Production of stable multidimensional solitary waves is a grand challenge in modern science. Steering their propagation is an even harder problem. Here we demonstrate three-dimensional solitary waves in a nematic, trajectories of which can be steered by the electric field in a plane perpendicular to the field. The steering does not modify the properties of the background that remains uniform. These localized waves, called director bullets, are topologically unprotected multidimensional solitons of (3 + 2)D type that show fore-aft and right-left asymmetry with respect to the background molecular director; the symmetry is controlled by the field. Besides adding a whole dimension to the propagation direction and enabling controlled steering, the solitons can lead to applications such as targeted delivery of information and micro-cargo. 

Abstract Electric field-induced collective reorientation of nematic molecules is of importance for fundamental science and practical applications. This reorientation is either homogeneous over the area of electrodes, as in displays, or periodically modulated, as in electroconvection. The question is whether spatially localized three-dimensional solitary waves of molecular reorientation could be created. Here we demonstrate that the electric field can produce particle-like propagating solitary waves representing self-trapped “bullets” of oscillating molecular director. These director bullets lack fore-aft symmetry and move with very high speed perpendicularly to the electric field and to the initial alignment direction. The bullets are true solitons that preserve spatially confined shapes and survive collisions. The solitons are topologically equivalent to the uniform state and have no static analogs, thus exhibiting a particle–wave duality. Their shape, speed, and interactions depend strongly on the material parameters, which opens the door for a broad range of future studies.