The relation of collective motion, defects, and potential energy landscape in 2D charged colloidal crystals

We utilize two-dimensional (2D) Yukawa crystals as an ideal platform to quantify collective motion in crystalline systems. To explore the interplay between defects and collective dynamics, we conduct molecular dynamics simulations of charged colloidal crystals. In these simulations, dust particle motion in a 2D dusty plasma crystal is modeled by considering particles as point charges, while the Brownian dynamics of charged particles with a core mimic the behavior of colloidal particles in a 2D colloidal crystal. To distinguish between thermal vibrations and rearrangements, we map particle configurations from real trajectories to their nearest energy-minimized inherent structures (IS). In the potential energy landscape, the system oscillates between defect-free ground states and discretized excited states incorporating defects. Notably, the average residence time in the ground and the excited states becomes exactly equal at the melting transition. The IS trajectory reveals extended periods in the defect-free ground state, interrupted by brief transitions to excited states where defect clusters appear, replacing particle clusters with string-like geometries. Furthermore, small collective ring exchanges occur even in the ground state without defects. Collective particle exchanges link defect clusters, ultimately facilitating their healing. This emerging picture suggests that diffusion in these systems is driven primarily by collective motion, mediated by defect clusters.