Hyperuniform mixing of binary active spinners

Abstract

Spinner mixtures consisting of both clockwise and counterclockwise self-spinning particles are often expected to phase separate. However, we demonstrate that such a demixing is absent for dimer (or rod-like) spinners. These particles always mix, even in a globally-hyperuniform way, with the total structure factor S(q → 0) ∼ q^α (α > 0). This global hyperuniformity can be enhanced or weakened by changes in the driving torques or the particle density. The corresponding microscopic mechanism is attributed to the competition between a dynamical heterocoordination effect and effective like-particle attractions. Critical scaling for the absorbing state transition of the system is also found to persist, with a significant shift in its critical point observed. The system can be further thermalized, by the driving torques or through thermostating, into an ideal solution with identical partial radial distribution functions, which denies the possibility of being multi-hyperuniform. A simply-extended coupled density-oscillator theory explains why the system cannot be multi-hyperuniform, but can have a global hyperuniformity with the scaling exponent α approaching 2. Such a hyperuniform mixing provides a way to regulate the topological boundary flows of this chiral system, and this mixing regulation is found to barely affect the bulk density fluctuations, or even preserve the localization of the flows and the bulk hyperuniformity.