Solitons in discrete linear chains of chiral smectic liquid crystals with competing interactions

Abstract

Chiral liquid crystals exhibit in-plane spontaneous polarizations, however, in their smectic (Sm) phase the primary-order parameter is the tilt vector associated with molecular rotations around the long axis parallel to the molecular directors. These molecular rotations can lead to several distinct phases among which an incommensurate order with a domain-wall texture is referred to as soliton. In this study, the formation of domain walls in smectic chiral (SmC) liquid crystals is analyzed, with emphasis on the competition between an Ising-like symmetric intermolecular interaction, an anti-symmetric intermolecular interaction due to molecular chirality and an applied in-plane electric field. It is found that the anti-symmetric intermolecular interaction increases the width of kink structures in the domain wall at moderate intensity of the y-component of the applied in-plane electric field. Increasing the x-component of the electric field creates unstable condition for soliton formation irrespective of magnitudes of the symmetric and chiral intermolecular interactions. The stability condition for single-kink structures in the discrete molecular chain is discussed, by estimating the Peierls stress experienced by the single-kink soliton. Results suggest that chirality lowers the Peierls–Nabarro barrier, hence increasing the lifetime of single-kink structures in the discrete medium.