Spatiotemporal order and emergent edge currents in active spinner materials

TL;DR

This study explores how self-spinning particles organize and transition between states, revealing emergent edge currents and novel phases driven by active rotations without self-propulsion.

Contribution

It introduces a theoretical and numerical analysis of self-spinning dimers, uncovering spatiotemporal order, active melting, and edge currents in active spinner materials, a less explored area.

Findings

Formation of phase-locked triangular lattice at low densities

Transition from spin model ground states to active melting with increasing density

Emergence of edge currents linked to chirality of active spinning

Abstract

Collections of interacting, self-propelled particles have been extensively studied as minimal models of many living and synthetic systems from bird flocks to active colloids. However, the influence of active rotations in the absence of self-propulsion i.e. spinning without walking) remains less explored. Here, we numerically and theoretically investigate the behaviour of ensembles of self-spinning dimers. We find that geometric frustration of dimer rotation by interactions yields spatiotemporal order and active melting with no equilibrium counterparts. At low density, the spinning dimers self-assemble into a triangular lattice with their orientations phase-locked into spatially periodic phases. The phase-locked patterns form dynamical analogues of the ground states of various spin models, transitioning from the 3-state Potts antiferromagnet at low densities to the striped herringbone phase of planar quadrupoles at higher densities. As the density is raised further, the competition between active rotations and interactions leads to melting of the active spinner crystal. Emergent edge currents, whose direction is set by the chirality of the active spinning, arise as a non-equilibrium signature of the transition to the active spinner liquid and vanish when the system eventually undergoes kinetic arrest at very high densities. Our findings may be realized in systems ranging from liquid crystal and colloidal experiments to tabletop realizations using macroscopic chiral grains.