Hydrogen-Ti$^{3+}$ Complex as a Possible Origin of Localized Electron Behavior in Hydrogen-Irradiated SrTiO$_3$

TL;DR

This study reviews muon spin rotation experiments and DFT calculations to explore how hydrogen-related defect complexes in SrTiO3 can lead to coexisting localized and delocalized electrons, explaining experimental observations.

Contribution

It demonstrates that hydrogen-irradiated SrTiO3 can host both localized and delocalized electrons due to specific defect complexes, supported by experimental and theoretical analysis.

Findings

Paramagnetic defect complex involves interstitial μ+ and Ti3+ small polaron.

A thermodynamic donor level forms just below the conduction band minimum.

Coexistence of localized and delocalized electrons is possible in hydrogen-irradiated SrTiO3.

Abstract

A recent muon spin rotation ($\mu^+$SR) study on a paramagnetic defect complex formed upon implantation of $\mu^+$ 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 $\mu^+$ 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.