79 research outputs found
Ordered droplet structures at the liquid crystal surface and elastic-capillary colloidal interactions
We demonstrate a variety of ordered patterns, including hexagonal structures
and chains, formed by colloidal particles (droplets) at the free surface of a
nematic liquid crystal (LC). The surface placement introduces a new type of
particle interaction as compared to particles entirely in the LC bulk. Namely,
director deformations caused by the particle lead to distortions of the
interface and thus to capillary attraction. The elastic-capillary coupling is
strong enough to remain relevant even at the micron scale when its
buoyancy-capillary counterpart becomes irrelevant.Comment: 10 pages, 3 figures, to be published in Physical Review Letter
Field-controlled dynamics of skyrmions and monopoles
Magnetic monopoles, despite their ongoing experimental search as elementary
particles, have inspired the discovery of analogous excitations in condensed
matter systems. In chiral condensed matter systems, emergent monopoles are
responsible for the onset of transitions between topologically distinct states
and phases, like in the case of transitions from helical and conical phase to
A-phase comprising periodic arrays of skyrmions. By combining numerical
modeling and optical characterizations, we describe how different geometrical
configurations of skyrmions terminating at monopoles can be realized in liquid
crystals and liquid crystal ferromagnets. We demonstrate how such complex
structures can be effectively manipulated by external magnetic and electric
fields. Furthermore, we discuss how our findings may hint at similar dynamics
in other physical systems, and their potential applications
Composite Skyrmion bags in two-dimensional materials
Skyrmions are particle-like topological excitations, studied in various
condensed matter systems and models of high-energy physics (HEP). They occur as
stable spin textures in certain planar magnetic materials and as configurations
in chiral nematic liquid crystals, having been originally proposed as model of
atomic nuclei. Since magnetic Skyrmions can be accelerated with a current, they
have the potential to encode bits in low-power magnetic storage devices.
Drawing on techniques from HEP, we demonstrate that magnetic and liquid crystal
Skyrmions interact like orientation dependent, localised particles, explaining
previously observed Skyrmion behaviour. This interaction motivates the
construction of Skyrmion bags: textures of high topological degree which we
realise experimentally in liquid crystals, and in magnetic materials by
computer simulations. These Skyrmion bags configurations are nested multiple
Skyrmions, which act like single Skyrmions in pairwise interaction, and under
the influence of a current in magnetic materials. These results emphasize
equivalent Skyrmion behaviour in different physical systems, and suggest new,
high-density magnetic memory storage devices based on Skyrmion bags.Comment: paper including methods and SI; 7 figures, 14 page
Electric-field-induced nematic-cholesteric transition and 3-D director structures in homeotropic cells
We study the phase diagram of director structures in cholesteric liquid
crystals of negative dielectric anisotropy in homeotropic cells of thickness d
which is smaller than the cholesteric pitch p. The basic control parameters are
the frustration ratio d/p and the applied voltage U. Fluorescence Confocal
Polarising Microscopy allows us to directly and unambiguously determine the 3-D
director structures. The results are of importance for potential applications
of the cholesteric structures, such as switchable gratings and eyewear with
tunable transparency based.Comment: Will be published in Physical Review
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