Metallic diluted dimerization in VO2 tweeds

Abstract

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 of strained VO2 films unveils the existence of multicomponent ferroelastic-martensitic tweed structures on ~5 nm length scales, well below the resolution limit of currently employed X-ray spectroscopic imaging techniques (Figure 1a). Density functional theory calculations show that such fine tweeds are formed by an unreported metallic structure (x3M), formed by partially dimerized V-chains, that appears tetragonal (rutile) on average, but is locally monoclinic (Figure 1b). 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 [2].