Emerging Topological Structures in Nematic Moiré Patterns

Topological defects are of fundamental interest to soft matter physics, particle physics, and mathematics. In liquid crystals, they are also of practical importance in sensing, photonics, and directed self-assembly of colloids and molecules. Rational design of topological defects with arbitrary morphology and periodicity could enable more practical applications of topological defects, which remains a challenge to date. Inspired by the moiré pattern, here we combine simulations and experiments to study nematic liquid crystal cells confined by two identical surface patterns. By a mechanical twist, we observe a rich variety of highly tunable, novel topological structures, which are sensitive to system geometries; the corresponding cross-polarized images are distinct from isotropic moiré patterns. Simulations also show that the Frederiks transition voltage is approximately 10% lower in nematic moiré patterned cells than in conventional planar twisted cells. As such, the proposed simple mechanical twist method shows the promise of designing and tuning arbitrary, external-field-responsive, mesoscopic structures and optical patterns in liquid crystals and beyond, which can facilitate applications in defect-templated self-assembly, display, imaging, and photonic devices.