Polar solitons in a nonpolar chiral soft matter system

TL;DR

This paper reports the discovery of polar solitons with nematic order in a nonpolar, chiral liquid crystal system, demonstrating their formation, dynamics, and potential applications in soft matter physics.

Contribution

It introduces the first observation of polar solitons in a nonpolar system, revealing their formation mechanism and dynamic behaviors under electric fields.

Findings

Polar solitons exhibit corn-kernel shape with topological defects.

Collision behaviors include repulsion and attraction, leading to soliton merging.

Electric and nematic elastic energies balance to form solitons, with flexoelectric effects influencing rotation.

Abstract

Polar solitons, i.e., solitonic waves accompanying asymmetry of geometry or phase, have garnered attention in polar systems, such as ferroelectric or magnetoelectric materials, where they play a critical role in topological transitions and nonreciprocal responses to external fields. A key question is whether such polar solitons can emerge in nonpolar systems, where intrinsic polarity is absent. Here, we demonstrate an unprecedented polar soliton with nematic order in a nonpolar and chiral liquid crystal system by applying an alternating electric field. The soliton is corn-kernel-shaped, displaying a pair of oppositely charged topological defects at its two ends. While head-to-head collision between the solitons leads to repulsion, head-to-tail collision attracts the solitons into a single polar soliton. A rich variety of solitonic kinetics, such as rectilinear translation and circulation motions, can be activated by controlling the voltage and frequency of an electric field. Simulations reveal that the formation of the polar solitons is achieved through balancing the electric and nematic elastic energies, while the flexoelectric effect drives their rotational behaviors. The discovery of polar solitons in nonpolar systems expands the understanding of topological solitons, opening new avenues for dynamic control in soft matter systems, with potential applications in nonreciprocal responsive materials and topological information storage.