Transition between ground states in square anisotropic artificial colloidal ice
In Artificial Colloidal Ice (ACI), paramagnetic colloidal particles are confined in double-well traps and interact via repulsive, isotropic, magnetic dipole-dipole interactions that can be controlled by an external magnetic field. In this paper, we dynamically introduce anisotropic interactions to ACI by rotating the external magnetic field, which, in equilibrium, makes the system go from a charge-free 2-in, 2-out ice rule state, to a charged 4-in, 4-out state. We observe a strong dependence of the final configuration on the field's rotation rate $ω$: at high angular velocity, the system achieves a defect free final state via a difussionless transformation from the initial ground state. However, counterintuitively, at slow rotation rates, ergodicity breaks down, trapping the system in a partially ordered metastable state.