Electric field driven reconfigurable multistable topological defect patterns

Abstract

Topological defects appear in symmetry breaking phase transitions and are ubiquitous throughout Nature. As an ideal testbed for their study, defect configurations in nematic liquid crystals (NLCs) could be exploited in a rich variety of technological applications. Here we report on robust theoretical and experimental investigations in which an external electric field is used to switch between predetermined stable chargeless disclination patterns in a nematic cell, where the cell is sufficiently thick that the disclinations start and terminate at the same surface. The different defect configurations are stabilized by a master substrate that enforces a lattice of surface defects exhibiting zero total topological charge value. Theoretically, we model disclination configurations using a Landau-de Gennes phenomenological model. Experimentally, we enable diverse defect patterns by implementing an in-house-developed atomic force measurement scribing method, where NLC configurations are monitored via polarized optical microscopy. We show numerically and experimentally that an "alphabet" of up to 18 unique line defect configurations can be stabilized in a 4 × 4 lattice of alternating s = ±1 surface defects, which can be "rewired" multistably using appropriate field manipulation. Our proof-of-concept mechanism may lead to a variety of applications, such as multistable optical displays and rewirable nanowires. Our studies also are of interest from a fundamental perspective. We demonstrate that a chargeless line could simultaneously exhibit defect-antidefect properties. Consequently, a pair of such antiparallel disclinations exhibits an attractive interaction. For a sufficiently closely spaced pair of substrate-pinned defects, this interaction could trigger rewiring, or annihilation if defects are depinned.

Topological transitions in an oscillatory driven liquid crystal cell

“…Likewise, considering inhomogeneous anchoring allows attracting and trapping umbilical defects and creating vortex lattices 18,19 . A similar effect can be achieved by the introduction of inhomogeneous electrodes [20][21][22][23] . The combined use of magnets and uniform electric field can induce umbilical defects and lattices 24 .…”

Topological Defects in Nematic Liquid Crystals: Laboratory of Fundamental Physics

“…For example, so‐called chargleess line defects are characterized by and , which are often temporary created in sudden LC phase changes. [ 9,28,29 ] Consequently, the far nematic field of such defects is not distorted and such defects could unwind into a defectless state.…”

High-Efficiency Spin-Related Vortex Metalenses

“…Therefore, vortex beams are extensively used in optical communication [36,37], quantum systems [38] and particle trapping [39]. Benefiting from the ultrathin and miniaturized nature of metasurfaces, a variety of vortex beam generators based on metasurfaces have been designed and studied [40][41][42][43]. Nevertheless, most vortex beam generators only produce one specific topological charge.…”