A General Mechanism for Emergent Chirality in Achiral Hard Particle Assembly

For centuries, chirality has been appreciated as a key component in understanding how matter orders.  While intuitively chiral particles can self-assemble into chiral superstructures, it is less clear how achiral particles are driven to do the same.  Here we show that there is a general mechanism that explains why many simple achiral particles can assemble into chiral materials.  Namely, we use simulations of hard, regular polygons to show that surprisingly subtle particle shape modifications, such as corner rounding, can induce chiral symmetry breaking by deforming the underlying close-packed lattice.  Not only does this mechanism quantitatively explain recent experimental results reporting chirality in the hard triangle system, but it offers an intuitive and general way by which chirality might emerge in nature.  Moreover, because effective corner rounding can be realized by modulating repulsive interactions, this simple mechanism suggests tremendous potential for creating dynamically tunable chiral surfaces with a variety of applications.