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Light control over topological charge in nematic liquid crystals

kibble.jpgAuthors M. Nikkhou, M. Škarabot, S. Čopar, M. Ravnik, S. Žumer and I. Muševič from Jožef Stefan Institute and Faculty of Mathematics and Physics (FMP), University of Ljubljana, have just reported on the discovery of light-control of the topological charge in the system of confined nematic liquid crystals. In the paper Light-controlled topological charge in a nematic liquid crystal, just published in the journal Nature Physics, they demonstrate that the confinement of space, specifically with microscopic colloidal fibres, affects the later stages of the Kibble-Zurek mechanism which allows for trapping and control of topological defect loops with different values of the topological charge. By using laser tweezers, they show that the dynamics of topologically charged objects can be well manipulated, including processes of repulsion and annihilation. The structure of ordering fields and the annihilation dynamics were determined also with intensive numerical modelling, using computer clusters which run at FMP. More generally, the demonstrated research reveals the sensitivity of the Kibble-Zurek mechanism on the connectedness of space and symmetry-breaking boundary conditions and further provides a new insight into key topological invariants of general topologically conditioned ordering fields.