Oxygen Vacancies in Strontium Titanate: a DFT+DMFT study

Abstract

We address the long-standing question of the nature of oxygen vacancies in strontium titanate, using a combination of density functional theory and dynamical mean-field theory (DFT+DMFT) to investigate in particular the effect of vacancy-site correlations on the electronic properties. Our approach uses a minimal low-energy electronic subspace including the Ti-$t_{2g}$ orbitals plus an additional vacancy-centered Wannier function, and provides an intuitive and physically transparent framework to study the effect of the local electron-electron interactions on the excess charge introduced by the oxygen vacancies. We estimate the strength of the screened interaction parameters using the constrained random phase approximation and find a sizeable Hubbard $U$ parameter for the vacancy orbital. Our main finding, which reconciles previous experimental and computational results, is that the ground state is either a state with double occupation of the localized defect state or a state with a singly-occupied vacancy and one electron transferred to the conduction band. The balance between these two competing states is determined by the strength of the interaction both on the vacancy and the Ti sites, and on the Ti-Ti distance across the vacancy. Finally, we contrast the case of vacancy doping in SrTiO${}_3$ with doping via La substitution, and show that the latter is well described by a simple rigid-band picture.

replaced with slightly revised version (response to peer review reports) and added journal reference

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Cited by in corpus (8)

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• Explicit demonstration of the equivalence between DFT+U and the Hartree-Fock limit of DFT+DMFT
• Single-site DFT+DMFT for vanadium dioxide using bond-centered orbitals
• BinPo: An open-source code to compute the band structure of two-dimensional electron systems
• High stability 2D electron gases formed in Si3N4/Al//KTaO3 heterostructures: synthesis and in-depth interfacial characterization
• Origin of Oxygen Partial Pressure-Dependent Conductivity in SrTiO3
• Stability and diffusion of oxygen vacancies in LaNiO${}_3$: a DMFT study
• Bridging constrained random-phase approximation and linear response theory for computing Hubbard parameters