Commensuration torques and lubricity in double moire systems

  We study the commensuration torques and layer sliding energetics of alternating twist trilayer graphene (t3G) and twisted bilayer graphene on hexagonal boron nitride (t2G/BN) that have two superposed moire interfaces. Lattice relaxations for typical graphene twist angles of~ 1° in t3G or t2G/BN are found to break the out-of-plane layer mirror symmetry, give rise to layer rotation energy local minima dips of the order of ~ 10^-1 meV/atom at double moire alignment angles, and have sliding energy landscape minima between top-bottom layers of comparable magnitude. Moire superlubricity is restored for twist angles as small as ~ 0.03° away from alignment resulting in suppression of sliding energies by several orders of magnitude of typically ~10^-4 meV/atom, hence indicating the precedence of rotation over sliding in the double moire commensuration process. We discuss the potential implications of our results in the preparation of experimental devices with angle aligned double moire patterns with specific top-bottom layer sliding atomic stacking geometries and how this can impact the electronic structure of the commensurate double moire systems considered.