Hydrogen-Ti3+ Complex as a Possible Origin of Localized Electron Behavior in Hydrogen-Irradiated SrTiO3

A recent muon spin rotation (μ + SR) study on a paramagnetic defect complex formed upon implantation of μ + pseudo-proton into SrTiO 3 is reviewed with a specific focus on the relation with experimental signatures of coexisting delocalized and localized electrons in hydrogen-irradiated metallic SrTiO 3 films. The paramagnetic defect complex, composed of interstitial μ + and Ti 3+ small polaron, is characterized by a small dissociation energy of about 30 meV. Density functional theory (DFT) calculations in the generalized gradient approximation (GGA) + U scheme for a corresponding hydrogen defect complex reveal that a thermodynamic donor level associated with electron transfer from an H + -Ti 3+ complex to the conduction band can form just below the conduction band minimum for realistic U values. These findings suggest that the coexistence of delocalized and localized electrons can be realized in hydrogen-irradiated SrTiO 3 in electron-rich conditions.