Revealing the Role of Hydrogen in Electron-Doping Mottronics for Strongly Correlated Vanadium Dioxide

Hydrogen-associated electron-doping Mottronics for d-band correlated oxides (e.g., VO₂) opens up a new paradigm to regulate the electronic functionality via directly manipulating the orbital configuration and occupancy. Nevertheless, the role of hydrogen in the Mottronic transition of VO₂ is yet unclear because opposite orbital reconfigurations toward either the metallic or highly insulating states were both reported. Herein, we demonstrate the root cause for such hydrogen-induced multiple electronic phase transitions by ¹H quantification using nuclear reaction analysis. A low hydrogenation temperature is demonstrated to be vital in achieving a large hydrogen concentration (n_H ≈ 10²² cm^-3) that further enhances the t_2g orbital occupancy to trigger electron localizations. In contrast, elevating the hydrogenation temperatures surprisingly reduces n_H to ∼10²¹ cm^-3 but forms more stable metallic H_0.06VO₂. This leads to the recognition of a weaker hydrogen interaction that triggers electron localization within VO₂ via Mottronically enhancing the orbital occupancies.