Spontaneous Vortex Instability in Active Nematics
Abstract
One of the defining results in the study of active matter is the spontaneous flow instability, through which a homogeneous, uniformly aligned state breaks translational symmetry along a single direction and develops sustained flow. The vortex state that emerges at higher activity has instead been attributed to nonlinear dynamics. Using a Floquet-type linear stability analysis, we show that no such mechanism is required: the flowing state undergoes a secondary, zigzag instability that breaks the remaining translational symmetry and produces the vortex state. We further identify a regime in which the flowing state ceases to exist and vortices emerge directly from the uniformly aligned state. Under channel confinement, the instability selects a length scale that differs from the establishedactivelengthscale, andsetsthenumberofvorticesthatappear, leadingtoaconfinement- selected pattern reminiscent of a vortex lattice, opening a route toward direct experimental tests of this instability. Full nonlinear simulations reproduce the predicted onset activities and the selected vortex number.
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BibTeX
@misc{sousa2026spontaneous,
title = {{Spontaneous Vortex Instability in Active Nematics}},
author = {Niels de Graaf Sousa and Kristian Thijssen and Amin Doostmohammadi},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.15093},
eprint = {2609.15093},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.15093},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Spontaneous Vortex Instability in Active Nematics
AU - Niels de Graaf Sousa
AU - Kristian Thijssen
AU - Amin Doostmohammadi
PY - 2026
DA - 2026/09/14
PB - arXiv
DO - 10.48550/arxiv.2609.15093
UR - https://arxiv.org/abs/2609.15093
AB - One of the defining results in the study of active matter is the spontaneous flow instability, through which a homogeneous, uniformly aligned state breaks translational symmetry along a single direction and develops sustained flow. The vortex state that emerges at higher activity has instead been attributed to nonlinear dynamics. Using a Floquet-type linear stability analysis, we show that no such mechanism is required: the flowing state undergoes a secondary, zigzag instability that breaks the remaining translational symmetry and produces the vortex state. We further identify a regime in which the flowing state ceases to exist and vortices emerge directly from the uniformly aligned state. Under channel confinement, the instability selects a length scale that differs from the establishedactivelengthscale, andsetsthenumberofvorticesthatappear, leadingtoaconfinement- selected pattern reminiscent of a vortex lattice, opening a route toward direct experimental tests of this instability. Full nonlinear simulations reproduce the predicted onset activities and the selected vortex number.
ER -