Frustrated liquid crystalline order in spherical shells

Confining a liquid crystal to a spherical shell usually entails the formation of topological defects, which are part of the ground state of the liquid crystal. Unlike flat geometries, the spherical geometry of shells ensures the stability of those defects providing a playground to study fundamental questions concerning the formation, interaction and structure of topological defects, which is central to many areas of physics. We are currently interested in studying the organization of a chiral nematic or cholesteric liquid crystal when confined to a spherical shell.

Waltzing defects in a cholesteric shell (movie)

Droplets of chiral liquid crystals typically exhibit an intriguing radial defect which results from frustrations in the molecular order. This configuration shows a fascinating analogy to the Dirac monopole, a hypothetical magnetic charge, and plays a crucial role in the droplet optical properties, recently exploited to produce microlasers. Despite its evident interest, the nature of this disclination remains uncertain. We have experimentally showed, by studying spherical cholesteric shells, that it is composed of two line defects that wrap around each other on a double-helix structure. By tuning the system chirality, we can make this configuration dissociate into two independent stacks of disclination rings. The transition between configurations is reversible and entails an unexpected defect waltz dynamics.