Commensuration torques and lubricity in double moire systems

N Leconte and Y Park and J An and J Jung, PHYSICAL REVIEW B, 110, 024109 (2024).

DOI: 10.1103/PhysRevB.110.024109

We study the commensuration torques and layer sliding energetics of twisted trilayer graphene (t3G) and twisted bilayer graphene on hexagonal boron nitride (t2G/BN) that have two contiguous superposed moire interfaces. Lattice relaxations for typical graphene twist angles of similar to 1 degrees 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 similar to 10(-1) meV/atom at double moire alignment angles, and have stacking energy minima of comparable magnitude between the next-nearest top-bottom layers. Thus, in t3G, the top and bottom layers tend to align when one twisted interface angle is fixed, whereas in t2G/BN, the alignment of the two moire patterns favors t2G with theta similar or equal to 1.12 degrees near the magic angle when the G/BN interface is rotated at theta similar or equal to 0.56 degrees. Precedence of rotation over sliding during the moire commensuration is confirmed for periodic boundary systems where the sliding energy barriers drop to similar to 10(-4) meV/atom for physical misalignment angles as small as similar to 0.03 degrees. For finite graphene flakes of diameter D, we find enhanced friction forces for a wider range of angles Delta theta(FWHM) similar to C/D both near the zero alignment angle in t2G and commensurate double moire angles in t3G.

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