LAUSR

Abstract Observation of superconductivity in twisted-bilayer-graphene and highly-oriented-pyrolytic-graphite (HOPG) for certain magic-angles-of-rotation has recently attracted an important attention. Unusual temperature-(T)-induced-shifts in the graphitic c-axis have also been reported in HOPG in conditions of θ misfit ∼ 1° (first-magic-angle). We report a novel investigation of HOPGs with θ misfit of 0.5°, 0.8°, 1.5°, ≫ 1.5° and of water-treated-turbostratic-graphite in the T-range from 298.15 to 673.15K. Presence of magic angles of rotations corresponding to the reported θ misfit values is demonstrated by repeated HRTEM and Moire pattern analyses of HOPG lamellae extracted from individual samples with scotch tape methods. Interestingly in our measurements the c-axis-shift is found to depend strongly on the misfit-angle, with the highest-values of 0.00428 and 0.00426 nm in proximity of the first-magic-angle (θ misfit ∼ 0.8° and ∼0.5°). Two diffraction-peaks present at ∼23.5° and ∼48.5° 2θ (detector angle, in typical Bragg- Brentano configuration) for θ misfit ∼1° are also found to vanish for θ misfit ≫ 1.5°. These findings imply existence of additional symmetry elements at the magic angle, which are not present in the standard space group notation used for structural characterization of graphite (P63/mmc).