Chirality, Kinks and Topological Defects on π Domain Walls in Ferroelectric Nematic Liquid Crystals

Domain walls that separate regions of different polarizations are ubiquitous in ferroelectric nematic liquid crystals. Here we report that the π walls in films of the polar fluids consist of twin half-integer surface disclinations spaced horizontally, enclosing a subdomain where the polarization exhibits left- or right-handed π twists across the film. The degenerate geometric arrangements of the twin disclinations generate kinks and antikinks, parting subdomains of opposite chirality, like the spin-up and spin-down in Ising chains. The hierarchical structures dictate that field-driven polar switching undergo two-step annihilations of the surface disclinations. We will further discuss other topological defects often observed along these walls.