Vortex triplets, symmetry breaking, and emergent nonequilibrium plastic crystals in an active-spinner fluid
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| Format: | Preprint |
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2025
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| author | Maji, Biswajit Padhan, Nadia Bihari Pandit, Rahul |
| author_facet | Maji, Biswajit Padhan, Nadia Bihari Pandit, Rahul |
| contents | The formation of patterns and exotic nonequilibrium steady states in active-fluid systems continues to pose challenging problems -- theoretical, numerical, and experimental -- for statistical physicists and fluid dynamicists. We combine theoretical ideas from statistical mechanics and fluid mechanics to uncover a new type of self-assembled crystal of vortex triplets in an active-spinner fluid. We begin with the two-dimensional Cahn-Hilliard-Navier-Stokes (CHNS) model for a binary-fluid system of active rotors that has two important ingredients: a scalar order parameter field phi that distinguishes regions with clockwise (CW) and counter-clockwise (CCW) spinners; and an incompressible velocity field u. In addition to the conventional CHNS coupling between phi and u, this model has a torque-induced activity term, with coefficient tau, whose consequences we explore. We demonstrate that, if we increase the activity tau, it overcomes dissipation and this system displays a hitherto unanticipated emergent triangular crystal, with spinning vortex triplets at its vertices. We show that this is a nonequilibrium counterpart of an equilibrium plastic crystal. We characterise the statistical properties of this novel crystal and suggest possible experimental realisations of this new state of active matter. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2509_09273 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Vortex triplets, symmetry breaking, and emergent nonequilibrium plastic crystals in an active-spinner fluid Maji, Biswajit Padhan, Nadia Bihari Pandit, Rahul Soft Condensed Matter Statistical Mechanics Adaptation and Self-Organizing Systems Biological Physics The formation of patterns and exotic nonequilibrium steady states in active-fluid systems continues to pose challenging problems -- theoretical, numerical, and experimental -- for statistical physicists and fluid dynamicists. We combine theoretical ideas from statistical mechanics and fluid mechanics to uncover a new type of self-assembled crystal of vortex triplets in an active-spinner fluid. We begin with the two-dimensional Cahn-Hilliard-Navier-Stokes (CHNS) model for a binary-fluid system of active rotors that has two important ingredients: a scalar order parameter field phi that distinguishes regions with clockwise (CW) and counter-clockwise (CCW) spinners; and an incompressible velocity field u. In addition to the conventional CHNS coupling between phi and u, this model has a torque-induced activity term, with coefficient tau, whose consequences we explore. We demonstrate that, if we increase the activity tau, it overcomes dissipation and this system displays a hitherto unanticipated emergent triangular crystal, with spinning vortex triplets at its vertices. We show that this is a nonequilibrium counterpart of an equilibrium plastic crystal. We characterise the statistical properties of this novel crystal and suggest possible experimental realisations of this new state of active matter. |
| title | Vortex triplets, symmetry breaking, and emergent nonequilibrium plastic crystals in an active-spinner fluid |
| topic | Soft Condensed Matter Statistical Mechanics Adaptation and Self-Organizing Systems Biological Physics |
| url | https://arxiv.org/abs/2509.09273 |