Spinning mixtures: nonreciprocity transfers chirality across scales in scalar densities

Abstract

A mixture of spinning particles of two different types represents a system where both nonreciprocity and chirality determine the emergent dynamics. In this work we present a minimal model for a two-species mixture of chiral active particles, formulated solely in terms of the number densities of the species. Both nonreciprocity and chirality enter the bulk part of the chemical potential, taking the form of local and non-local contributions, respectively. The chiral term manifests as the curl of the nonreciprocal current, which is non-zero when chasing interactions produces a local phase shift between the number densities. Chiral domains are localised and, as a result of number conservation, they have either positive or negative sign. The chiral domains pull in or push out particles depending on their sign and strongly modify the nonreciprocal dynamics. Their interplay generates distinctive dynamical states, including phase separation with edge currents and a spatio-temporally disordered phase with both chiral and nonreciprocal signatures.