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Metallic Diluted Dimerization in VO2 Tweeds

The observation of electronic phase separation textures in vanadium dioxide (VO2), a prototypical electron-correlated oxide, has recently added new perspectives on the long standing debate about its metal-insulator transition and its applications. Yet, the lack of atomically-resolved information on phases accompanying such complex patterns still hinders a comprehensive understanding of the transition and its implementation in practical devices. In this work, atomic resolution imaging and spectroscopy unveils the existence of ferroelastic tweed structures on ~5 nm length scales, well below the resolution limit of currently employed spectroscopic imaging techniques. Moreover, density functional theory calculations show that such fine tweeds are formed by a metallic structure, formed by partially dimerized V-chains, that appears tetragonal (rutile) on average, but is locally monoclinic. These observations suggest that the metal/insulator coexistence among low-symmetry forms of VO2 is driven by lattice degrees of freedom, and provide a multiscale perspective for the interpretation of existing data, whereby phase coexistence and structural intermixing can occur all the way down to the atomic scale.