Soliton walls paired by polar surface interactions in a ferroelectric nematic liquid crystal

TL;DR

This paper reveals how polar surface interactions in ferroelectric nematic liquid crystals create unique domain structures, including paired 360-degree walls, influenced by surface polarity and elastic constants.

Contribution

It demonstrates the formation of paired 360-degree domain walls in ferroelectric nematic liquid crystals due to in-plane surface polarity, a novel insight into surface-induced domain structures.

Findings

Polar in-plane surface interactions induce monodomains and stripe domains.

Paired 360-degree domain walls are stabilized by surface polarity.

Splay elastic constant exceeds bend modulus in these structures.

Abstract

Surface interactions are responsible for many properties of condensed matter, ranging from crystal faceting to the kinetics of phase transitions. Usually, these interactions are polar along the normal to the interface and apolar within the interface. Here, we demonstrate that polar in-plane surface interactions of a ferroelectric nematic NF produce polar monodomains in micron-thin planar cells and stripes of an alternating electric polarization, separated by 180 degree domain walls, in thicker slabs. The surface polarity binds together pairs of these walls, yielding a total polarization rotation by 360 degrees. The polar contribution to the total surface anchoring strength is on the order of 10%. The domain walls involve splay, bend, and twist of the polarization. The structure suggests that the splay elastic constant is larger than the bend modulus. The 360 degree pairs resemble domain walls in cosmology models with biased vacuums and ferromagnets in an external magnetic field.