Interlayer commensurability and superlubricity in rigid layered materials

Superlubricity is a frictionless tribological state sometimes occurring in nanoscale material junctions. It is often associated with incommensurate surface lattice structures appearing at the interface. Here, by using the recently introduced registry-index concept that quantifies the registry mismatch in layered materials and reproduces their interlayer sliding energy landscape, we prove the existence of a direct relation between interlayer commensurability and wearless friction in rigid layered materials. We show that our simple and intuitive model is able to capture, down to fine details, the experimentally measured frictional behavior of a hexagonal graphene flake sliding on top of the surface of graphite. We further predict that superlubricity is expected to occur in hexagonal boron nitride as well with tribological characteristics very similar to those observed for the graphitic system. The success of our method in predicting experimental results along with its high computational efficiency marks the registry index as a promising tool for studying tribological properties of nanoscale material interfaces.