Skyrmions are particle-like topological entities in a continuous field that have a role in various condensed matter systems. Here, numerical methods are used to show that a chiral nematic liquid crystal could be used as a model system to facilitate direct structural investigation of Skyrmions.

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Quasi-two-dimensional Skyrmion lattices in a chiral nematic liquid crystal.

An experimental review on electric field effects in blue phases is presented. Electric fields have a profound effect on these phases which appear in chiral liquid crystals. In addition to producing elec-trostrictive effects on blue phase lattices, they also cause new field induced phases—tetragonal BPX, hexagonal BPH3D and BPH2D, and possible other phases yet to be identified. In recent experiments on BPIII for materials with negative dielectric anisotropy, it was found that electric fields cause a dramatic increase in the otherwise weak BPIII selective reflection. These experimental results were discussed with respect to possible models for the unknown structure of BPIII. Recently, efforts were also made to investigate the dynamics of different electrooptic effects more precisely.

/pdf/the-effect-of-electric-fields-on-blue-phases-20kpigfzva.pdf

The effect of electric fields on blue phases

An introductory review of the cholesteric blue phases is presented. The emphasis is on the basic concepts of the theoretical framework and the recent achievements of theory and experiment. The author discusses a number of controversial issues indicating where future research is expected to shed light on the remaining unresolved problems.

https://iopscience.iop.org/article/10.1088/0034-4885/53/6/001/pdf

The liquid-crystalline blue phases

In Chap.3 we considered the interaction between Mossbauer (short wave) radiation and crytals within the framework of diffraction theory. Here we demonstrate that the same approach describes the interaction between optical (long wave) radiation and periodic media of complex structure, specifically, chiral liquid crystals.

Optics of Chiral Liquid Crystals

The occurrence of a three dimensional hexagonal blue phase BPH (possible space groups P6222 and P6422) in materials with negative dielectric anisotropy ϵa = ϵ∥ - ϵ⊊ has been detected by the investigation of Kossel diagrams. This is the first observation of a field-induced transition between different blue phase modifications for systems with ϵa 0 (four-fold axis parallel to th...

Observation of a hexagonal blue phase in systems with negative dielectric anisotropy

Using Landau theory, the possibility that two and three dimensional hexagonal structures can exist in cholesteric liquid crystals with positive dielectric anisotropy in an applied electric or magnetic field is considered. Both are found to be thermodynamically stable in different regions of the chirality-temperature-field phase diagram, in agreement with reported experimental data. Further, the theoretical results indicate that two different three dimensional hexagonal phases, having the same space group (P6222) but different structure factors, may exist. Ways of verifying this prediction by optical and N.M.R. studies are considered. Also noted is the need to develop further the theoretical model to allow for the existence of the experimentally observed body-centred tetragonal structure.

S. Shtrikman

Papers

Invited Lecture. Hexagonal cholesteric blue phases