Observation of Superlubricity at Commensurate Moiré Graphite Interfaces

Commensurability and incommensurability are core concepts that permeate the field of structural superlubricity; among them, commensurate moiré patterns form a special class of configuration whose frictional properties have remained experimentally unexplored. Here we report the first direct observation of sharp friction peaks at 21.8° and 38.2° relative orientations of graphite interface corresponding to the (2, 1) commensurate moiré pattern, while other (m,n) commensurate moiré patterns show no detectable signal. Unlike the observable load dependence at the coaligned commensurate state, these peaks display negligible load dependence, resembling superlubric behavior, analogous to incommensurate interface. Theoretical analysis and atomistic simulations reveal that sliding barriers decay exponentially with increasing (m,n) indices, leaving only a minimal residual sliding barrier and remarkably stable interlayer separation-effectively approaching a state of "van der Waals levitation." Our results complete the angular frictional landscape of two-dimensional homointerfaces and establish that higher-order commensurability is already sufficient to realize structural superlubricity.