Topological states in chiral active matter: Dynamic blue phases and active half-skyrmions

Metselaar, Luuk; Doostmohammadi, Amin; Yeomans, J. M.

doi:10.1063/1.5085282

Cited by 30 publications

(19 citation statements)

References 48 publications

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“…Topologically, the key difference is that in 2D nematic fields only +1/2 and −1/2 defects are possible, whereas in 3D nematics the defects can be in the from of points, loops or walls, and even lines if these can terminate appropriatelly like on surfaces. Also, solitonic solutions are starting to be seen in objects like active skyrmions [35]. These three-dimensional nematic defect structures can be characterised with different topological invariants (in 2D nematics there is only 2D topological charge) that account for the topology of the defects as a whole, such as 3D topological charge, linking and self-linking number.…”

Section: Discussionmentioning

confidence: 99%

Topology of Three-Dimensional Active Nematic Turbulence Confined to Droplets

et al. 2019

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Active nematics contain topological defects which under sufficient activity move, create and annihilate in a chaotic quasi-steady state, called active turbulence. However, understanding active defects under confinement is an open challenge, especially in three-dimensions. Here, we demonstrate the topology of three-dimensional active nematic turbulence under the spherical confinement, using numerical modelling. In such spherical droplets, we show the three-dimensional structure of the topological defects, which due to closed confinement emerge in the form of closed loops or surface-to-surface spanning line segments. In the turbulent regime, the defects are shown to be strongly spatially and time varying, with ongoing transformations between positive winding, negative winding and twisted profiles, and with defect loops of zero and non-zero topological charge.The timeline of the active turbulence is characterised by four types of bulk topology-linked events -breakup, annihilation, coalescence and cross-over of the defects -which we discuss could be used for the analysis of the active turbulence in different three-dimensional geometries. The turbulent regime is separated by a first order structural transition from a low activity regime of a steady-state vortex structure and an offset single point defect. We also demonstrate coupling of surface and bulk topological defect dynamics by changing from strong perpendicular to inplane surface alignment. More generally, this work is aimed to provide insight into three-dimensional active turbulence, distinctly from the perspective of the topology of the emergent three-dimensional topological defects. * These authors contributed equally to this work.

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Section: Discussionmentioning

confidence: 99%

Topology of Three-Dimensional Active Nematic Turbulence Confined to Droplets

et al. 2019

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“…Especially, it is important to realise that defect lines and loops in three-dimensional active nematics can exhibit a full span of different local orientational profiles -of ±1/2 wedge, twist and mixed type -which results in profoundly different local self-propulsion velocities, both in the directions perpendicular and along the defect loop segment. There are many natural directions for extension of our work, including to a detailed com- parison of topologically charged and uncharged loops [11] and to defects in active cholesterics [31,32]. The significance of two-dimensional topological defects to biological systems such as cell cultures and tissues has been wellestablished in recent years [5][6][7]; active defect loops may provide similar insights to fully three-dimensional biological tissues, fluids and processes.…”

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confidence: 99%

Three-Dimensional Active Defect Loops

et al. 2020

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We describe the flows and morphological dynamics of topological defect lines and loops in threedimensional active nematics and show, using theory and numerical modelling, that they are governed by the local profile of the orientational order surrounding the defects. Analysing a continuous span of defect loop profiles, ranging from radial and tangential twist to wedge ±1/2 profiles, we show that the distinct geometries can drive material flow perpendicular or along the local defect loop segment, whose variation around a closed loop can lead to net loop motion, elongation or compression of shape, or buckling of the loops. We demonstrate a correlation between local curvature and the local orientational profile of the defect loop, indicating dynamic coupling between geometry and topology. To address the general formation of defect loops in three dimensions, we show their creation via bend instability from different initial elastic distortions.

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“…Our results for the pulse drive suggest that the net forward or backward motion originates from a nonlinear drag effect that is produced by asymmetric ac oscillations in the skyrmion shape. Beyond LC skyrmions, the effects we observe could also be relevant for skyrmions in magnetic systems or for soft matter systems containing bubble like shapes such as vesicles undergoing some sort of asymmetric periodic shape change or expansion [32]. It would also be interesting to couple this motion to some kind of substrate in order to generate controlled directed motion.…”

Section: Discussionmentioning

confidence: 91%

Directed Motion of Liquid Crystal Skyrmions With Oscillating Fields

Duzgun,

Nisoli,

Reichhardt

et al. 2021

Preprint

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Using continuum simulations, we show that under a sinusoidal electric field, liquid crystal skyrmions undergo periodic shape oscillations which produce controlled directed motion. The speed of the skyrmion is non-monotonic in the frequency of the applied field, and exhibits multiple reversals of the motion as a function of changing frequency. We map out the dynamical regime diagram of the forward and reverse motion for two superimposed ac driving frequencies, and show that the reversals and directed motion can occur even when only a single ac driving frequency is present. Using pulsed ac driving, we demonstrate that the motion arises due to an asymmetry in the relaxation times of the skyrmion shape. We discuss the connection between our results and ratchet effects observed in systems without asymmetric substrates.

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Topological states in chiral active matter: Dynamic blue phases and active half-skyrmions

Cited by 30 publications

References 48 publications

Topology of Three-Dimensional Active Nematic Turbulence Confined to Droplets

Topology of Three-Dimensional Active Nematic Turbulence Confined to Droplets

Three-Dimensional Active Defect Loops

Directed Motion of Liquid Crystal Skyrmions With Oscillating Fields

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