Monopole-mediated light control of half skyrmion topology in nematic liquid crystals.

Skyrmions, with their robust topologically protected properties, have demonstrated significant potential for applications in spintronic devices. Despite their promise, the manipulation of topological invariants within these protected structures has remained a complex challenge. In this work, we present a method to orchestrate the topological transformation of half skyrmions through monopoles, which are singular point defects endowed with nontrivial topological charges. Through experiments and simulations, we identified eight distinct types of emergent monopoles. The mutual transformation between different half skyrmions can be induced by manipulating the profiles of topologically protected monopoles with light irradiation. Furthermore, a pair of monopoles and antimonopoles exhibit both attractive and repulsive interactions, depending on the topological structure of the half skyrmion that separates them. Leveraging the dynamic characteristics of monopoles, we have effectively used them as carriers for colloidal particles. This study of topological transitions in nematic liquid crystals offers valuable insights into fundamental physical phenomena and enhances our grasp of the subtle dynamics of topological matter, potentially leading to advances in the design of smart materials and devices with novel functionalities.