Depinning transition and 2D superlubricity in incommensurate colloidal monolayers

Colloidal monolayers sliding over periodic corrugated potential are highly tunable systems allowing to visualize the dynamics between crystalline surfaces [1]. Based on molecular dynamics, Vanossi and coworkers [2] reproduced the main experimental results and explored the potential impact of colloid sliding in nanotribology. The degree of interface commensurability was found to play a major role in determining the frictional properties, the static friction force Fs becoming vanishingly small in incommensurate geometries for weak corrugation U0.Lead by this result,here we systematically investigate the possibility to observe a 2D Aubry-like transition [3] from a superlubric state to a pinned state for increasing U0. By using a reliable protocol, we generate annealed configurations at different values of U0 for an underdense monolayer. We find Fs to be vanishingly small up to a critical corrugation Uc coinciding with an abrupt structural transition in the ground state configuration. Similarly to what is observed in the Frenkel Kontorova model,this transition is characterized by a significant decrease in the number of particles sampling regions near the maxima of the substrate potential.\\[4pt] [1] T. Bohlein, Nat. Mat.,11,126; [2] A. Vanossi, PNAS USA,109,16426; [3] S. Aubry, Phys.D,8,381.