"Spin" Dynamics in Buckled and Frustrated Quasi-two-dimensional Colloidal Crystals*

We experimentally study the structure and dynamics of quasi-two-dimensional (2D) colloidal crystals [Nature 456, 898 (2008)] with frustrated interparticle interactions. The 2D triangular lattice is formed by confining a monolayer of close-packed micro-spheres between two parallel cover glass plates. The wall separation is slightly larger than one particle diameter, facilitating formation of a buckled monolayer of particles. While each particle can occupy either up or down position (“spin” direction) on its lattice site, neighboring particles favor opposite positions, which frustrates a third neighboring particle in a triangular lattice (analogous to the Ising antiferromagnet on a triangular lattice). With video microscopy and particle tracking we determine the in-plane and vertical motion of each particle. Then, using Markov state models, we extract the equilibrium distribution of ground states and the transition rates between them. Preliminary results reveal a hierarchy of time scales associated with relaxation in this frustrated system.