A transition in lively nematics produces gradual, strongly interacting defects, a behaviour confirmed in residing cells
Nematics are supplies fabricated from rod‑like particles that are inclined to align in the identical course. In lively nematics, this alignment is consistently disrupted and renewed as a result of the particles are pushed by inside organic or chemical power. Because the orientation discipline twists and reorganises, it creates topological defects-points the place the alignment breaks down. These defects are central to the collective behaviour of lively matter, shaping flows, patterns, and self‑organisation.
On this work, the researchers establish an lively topological part transition that separates two distinct regimes of defect organisation. Because the system approaches this transition from beneath, the dynamics gradual dramatically: the comfort of defect density turns into sluggish, fluctuations within the variety of defects develop in amplitude and lifelong, and the system turns into more and more delicate to small modifications in exercise. On the crucial level, defects start to work together over lengthy distances, with correlation lengths that develop with system dimension. This behaviour produces a placing twin‑scaling sample, defect fluctuations seem uniform at small scales however turn into anti‑hyperuniform at bigger scales, which means that the variety of defects varies excess of anticipated from a random distribution.
A key discovering is that this anti‑hyperuniformity originates from defect clustering. Moderately than forming ordered constructions or present process part separation, defects have a tendency to seem close to present defects, creating multiscale clusters. This distinguishes the transition from effectively‑identified defect‑unbinding processes such because the Berezinskii-Kosterlitz-Thouless transition in passive nematics or the nematic-isotropic transition in screened lively techniques. Above the crucial exercise, the system enters a defect‑laden turbulent state the place defects are extra uniformly distributed and correlations turn into brief‑ranged and destructive.
The researchers verify these behaviours experimentally utilizing massive‑discipline‑of‑view measurements of endothelial cell monolayers that are the cells that line blood vessels. The identical twin‑scaling behaviour, lengthy‑vary correlations, and clustering seem in these residing tissues, demonstrating that the transition is strong throughout system sizes, parameter variations, frictional damping, and boundary situations.
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Energetic part separation: new phenomenology from non-equilibrium physics M E Cates and C Nardini (2025)
