Metal-insulator transition tuned by oxygen vacancy migration across TiO₂/VO₂ interface

Oxygen defects are essential building blocks for designing functional oxides with remarkable properties, ranging from electrical and ionic conductivity to magnetism and ferroelectricity. Oxygen defects, despite being spatially localized, can profoundly alter global properties such as the crystal symmetry and electronic structure, thereby enabling emergent phenomena. In this work, we achieved tunable metal-insulator transitions (MIT) in oxide heterostructures by inducing interfacial oxygen vacancy migration. We chose the non-stoichiometric VO_2-δ as a model system due to its near room temperature MIT temperature. We found that depositing a TiO₂ capping layer on an epitaxial VO₂ thin film can effectively reduce the resistance of the insulating phase in VO₂, yielding a significantly reduced R_OFF/R_ON ratio. We systematically studied the TiO₂/VO₂ heterostructures by structural and transport measurements, X-ray photoelectron spectroscopy, and ab initio calculations and found that oxygen vacancy migration from TiO₂ to VO₂ is responsible for the suppression of the MIT. Our findings underscore the importance of the interfacial oxygen vacancy migration and redistribution in controlling the electronic structure and emergent functionality of the heterostructure, thereby providing a new approach to designing oxide heterostructures for novel ionotronics and neuromorphic-computing devices.