Partial commensuration and Amontons laws of friction adapted for large atomic interfaces

We employ a minimal atomistic friction model to investigate the commensuration at interfaces when a large number of atoms are involved. As the normal load at the interface increases, we found a smooth transition from the ultralow friction (superlubricity) regime to the high-frictional motion via a gradual growth of the commensurate region where only a fraction of the atoms adjust their atomic arrangement according to the substrate surface potential. The center of mass of the sliding particle may lack the perfect periodicity of the conventional stick-slip motion in this partial commensuration state. The commensurate region is assigned as the effective contact, based on which the scaling behavior of friction can be explained in analogy to the classical Amontons law of friction. The revealed emergent state for large atomic sliders would be beneficial to studies on extending the fundamental frictional investigations to larger length scales.