Multistimuli-Controlled Topological Nucleation of Skyrmion Loops and Monopoles in Liquid Crystals

Topological solitons hold great promise for revolutionizing information and energy technologies, yet their controlled creation remains a major challenge. Here, we demonstrate room-temperature nucleation of fractional, skyrmion loops-three-dimensional, half-integer topological defects-within a nematic liquid crystal microfluidic cell. A single beam of linearly polarized light rotates the surface alignment, accumulating elastic twist until a topologically trivial texture collapses into a robust skyrmion loop. The loop's cross section continuously morphs between half Néel skyrmions, antiskyrmions, and bimerons. Real-time polarized microscopy and Landau-de Gennes free energy based simulations reveal that the transition occurs via a 2π twist discontinuity and a sharp energy drop. The same protocol can be triggered by electric fields or local heating, and spawns a pair of ±1 topological monopoles that migrate along the loop to minimize the free energy. Our findings establish nematic liquid crystals as an optically rewritable, low-energy platform for generating arbitrary three-dimensional topological textures, offering immediate avenues for reconfigurable photonics and topological metamaterials.