Flexoelectric Switching of Lock-and-Key Topological Bits

Abstract

Topological defects in nematic liquid crystals are high-energy sites of reduced order. We show that a point defect can be stabilized in pillbox-shaped pores. The pore shape promotes lock-and-key docking similar to that observed for colloidal particles. The defect docks in one lobe or the other, displaying bistability. Furthermore, the defect moves like a charged object in an external electric field. An in-plane field drives the defect from one lobe to the opposite lobe, where it remains once the field is removed. The velocity is linear in field strength and reverses with polarity, consistent with flexoelectric coupling. Within the pore, the nematic around the defect carries a positive bulk bound charge density, compensated by negative space charge in the rest of the fluid and on the bounding surfaces. The external field breaks the mirror symmetry of the pore and drives the defect motion. Defect displacement increases the component of the net dipole in the domain along the field. Antagonistic curvature in peanut-shaped pores repels the defect, allowing pore geometry to set distinct switching thresholds. The defects, while not topologically required, are long lived, so information can be stored in their position, allowing them to serve as topological bits. Arrays of topological bits store and rewrite binary information in defect positions, offering a route to reconfigurable, field-addressable soft materials.