Three-dimensional solitary waves with electrically tunable direction of propagation in nematics

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.

Soliton-induced liquid crystal enabled electrophoresis

“…3(d). This director dynamics is thus similar to that of the director inside the particle-free 90 B l directrons at low frequency reported in [5]. 15 B l dress is shown in Fig.…”

“…The present work shows that the tangentially anchored spheres become electrophoretically active through formation of electricallytriggered directron dresses around them. These directron dresses are similar to the 3D particle-like solitary waves called directrons and described earlier for high [4] and low [5] frequencies of an electric field acting on a uniformly aligned nematic. The speed of spheres grows with the square of the field, similarly to the conventional LCEP, but with that difference that the LCEP shows no threshold behavior while the effect described in this work does show a threshold behavior.…”

“…Electrically induced directron dresses around the spheres, however, bring about a necessary polar symmetry in the structure and render the tangentially anchored spheres electrophoretically active under the AC field. The structure of the directrons that form above some electric field threshold is similar to the directrons described for uniformly aligned nematics without colloids [4,5]. The directron-dressed spheres move in the plane perpendicular to E ; depending on the frequency or amplitude of the field, the spheres can move parallel, perpendicularly or at some angle to the uniform background director 0 n .…”

“…It is commonly known that solitons can survive collisions and restore their shape and propagation mode in head-to-head encounters [15]. The same is true for the standing-alone directrons [4,5]. This feature is the ultimate reason for the term "soliton", as it stresses particle-like properties of the solitary waves [16].…”

“…The in-plane azimuthal distortions do not change their curvature when the polarity of the voltage is reversed. To determine the period and polarity of out-of-plane director oscillation, we used oblique propagation of light [4,5]. The cell is tilted so that the light beam of the polarizing optical microscope enters the cell at the angle 15    from the normal to the cell [4,5].…”