Aubry pinning transition of twisted two-dimensional material bilayers

Bilayers of 2D materials such as graphene are frictionally pinned at perfect alignment but free sliding (``superlubric'') at large twists. Small-twist bilayers, heavily reconstructed, might equally remain superlubric, or turn spontaneously pinned through a so-called Aubry transition. Here, simulation and theory show that small twist graphene and other 2D bilayers remain unpinned even under high loads. A geometric criterion useful for future microscale friction planning---the width of moir\'e domain walls larger than four lattice spacings---characterizes this robust superlubricity.