Light-controlled of topological charge in a nematic liquid crystal (Faculty of Mathematics and Physics, University of Ljubljana)

Authors:Maryam Nikkhou, Miha Škarabot, Simon Čopar, Miha Ravnik, Slobodan Žumer, Igor Muševič

Members of the Jožef Stefan Institute and Faculty of Mathematics and Physics of the University of Ljubljana have published an article entitled "Light-controlled topological charge in a nematic liquid crystal" in the journal Nature Physics. This article describes the experiment and theoretical analysis where strong laser light was used to create and stabilise one or a multitude of pairs of topological defects in the nematic liquid crystal. Each defect-pair is formed of a defect and an anti-defect, which are the equivalent to a particle and an anti-particle in particle physics.

Topological charges are sources of physical fields which always appear in a pair comprising a particle and its anti-particle that can mutually annihilate into a vacuum. A well-known example of such a particle-anti-particle pair is the electron and its anti-particle – the positron. Each of these particles is the source of the electrical field, which binds electrons and nuclei into full atoms and molecules as a result of the electric field force between the charges. For elementary particles, the formation of a particle-antiparticle pair usually requires huge kinetic energy, which can be delivered during particle collisions in large particle accelerators and colliders.

Scientists of the Jožef Stefan Institute and the University of Ljubljana have discovered a simple method of creating stable pairs of topological charges in nematic liquid crystal by using strongly focused laser light, directed under an optical microscope into the nematic liquid crystal. By using the light’s force, they have explored the fundamental force between topological charges in the nematic liquid crystal. Their work is important for experimental topology because it allows for direct testing of fundamental principles of mathematical topology of fields. Their work is also of practical importance, as it is possible to use the force between topological charges to bind micro-photonic elements such as lasers and fibres into photonic micro-devices. This work might also be important for cosmology, as it relates to the influence of the topology of space on the production of the topological charge.

Source: Nikkhou, M., Škarabot, M., Čopar, S., Ravnik, M., Žumer, S., & Muševič, I. (2015). Light-controlled topological charge in a nematic liquid crystal. Nature Physics, 11(2), 183-187.