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., VO 2 ) 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 VO 2 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 1 H quantification using nuclear reaction analysis. A low hydrogenation temperature is demonstrated to be vital in achieving a large hydrogen concentration ( n H ≈ 10 22 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 ∼10 21 cm -3 but forms more stable metallic H 0.06 VO 2 . This leads to the recognition of a weaker hydrogen interaction that triggers electron localization within VO 2 via Mottronically enhancing the orbital occupancies.