The Synchronous to Exchange Transition in Magnetically Driven Colloidal Dimers

Abstract

AbstractNumerical simulations are used to investigate the collective dynamics of an ensemble of driven paramagnetic colloidal particles confined between two plates. The particles are subjected to an external precessing field and, depending on the field frequency and cell thickness, they can assemble into rotating dimers, up and down binary crystals or dynamic states characterized by particle exchange between nearest dimers. We characterize the transition between the synchronous and the exchange state by measuring the fraction of “active” particles, namely colloids that do not stroboscopically recover their original place in a Voronoi cell. We find that the relaxation time decreases algebraically with the reduced frequency and that the transition displays signatures of an absorbing phase transition.