Bubble phase induced by odd interactions in chiral systems

We study a chiral system of particles subject to both odd interactions and standard repulsive interactions. The interplay between oddness and inertia induces a non-equilibrium phase transition from a homogeneous to a non-homogeneous phase, characterized by the emergence of bubbles due to odd interactions. This phenomenon occurs in the absence of attractions and results from the competition between pressures, arising from particle repulsion, which tends to shrink the bubble, and an effective surface force that promotes its expansion. The latter is an effective centrifugal force associated with the circular motion of particles along the bubble's surface, driven by transverse interactions. As a signature of the phase transition, the system exhibits vortex structures and oscillating spatial velocity correlations, which emerge near the analytically predicted transition point. Our findings can be tested in granular experiments involving odd interactions, such as spinners and active granular particles, and could be crucial for characterizing the emergent properties of metamaterials.