Topological defects (TDs) appear in all branches of physics due to the simplicity of generic mechanisms: The necessary condition for their existence is spontaneous symmetry breaking in a relevant physical field. Nematic liquid crystals (NLCs) represent an ideal testbed for their study and they can display point, line, textures, and in favorable conditions also wall defects. TDs in NLCs can be relatively easily created, controlled, and experimentally observed. This enables a detailed and controlled analysis of their physical properties, leading to the cross‐fertilization of knowledge among different areas of physics, including condensed matter, particle physics, and cosmology. Furthermore, TDs in NLCs could be exploited in diverse applications. Herein, some salient features of most common TDs in NLCs, their generic mechanisms, their importance for fundamental science, and possible applications based on them are illustrated.
Basic natural entities seems to be physical fields. From this perspective elementary particles should correspond to robust localized field configurations. Most probable candidates for such configurations are topological defects. They are topologically protected and they exhibit robust body-like features. Particularly adequate structures are line defects which could display also linked or knotted configurations. Such structures could be relatively easily created, manipulated and observed in nematic liquid crystals. In this contribution we focus on nematic elementary line defects characterised by winding number |m|=½. We illustrate that they behave as line-like robust elastic objects. However, they could be reconfigured into qualitatively different conformations where topological conservation rules are obeyed. Keywords: Fields; Topological defects; Topological charge; Disclinations; Liquid crystals
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