Origin of band gaps in 3d perovskite oxides

TL;DR

This paper demonstrates that the band gaps in 3d perovskite oxides primarily originate from structural distortions and electronic instabilities, which can be effectively modeled using density functional theory without invoking strong correlations.

Contribution

It shows that a mean-field DFT approach can accurately describe the properties of 3d perovskite oxides and explains their insulating behavior through structural and electronic instabilities.

Findings

Band gaps are mainly due to symmetry-lowering distortions.

DFT successfully models the entire 3d perovskite series.

Insulation arises from structural and electronic instabilities.

Abstract

With their broad range of magnetic, electronic and structural properties, transition metal perovskite oxides ABO3 have long served as a platform for testing condensed matter theories. In particular, their insulating character - found in most compounds - is often ascribed to dynamical electronic correlations through the celebrated Mott-Hubbard mechanism where gaping arises from a uniform, symmetry-preserving electron repulsion mechanism. However, structural distortions are ubiquitous in perovskites and their relevance with respect to dynamical correlations in producing this rich array of properties remains an open question. Here, we address the origin of band gap opening in the whole family of 3d perovskite oxides. We show that a single-determinant mean-field approach such as density functional theory (DFT) successfully describes the structural, magnetic and electronic properties of the whole series, at low and high temperatures. We find that insulation occurs via energy-lowering crystal symmetry reduction (octahedral rotations, Jahn-Teller and bond disproportionation effects), as well as intrinsic electronic instabilities, all lifting orbital degeneracies. Our work therefore suggests that whereas ABO3 oxides may be complicated, they are not necessarily strongly correlated. It also opens the way towards systematic investigations of doping and defect physics in perovskites, essential for the full realization of oxide-based electronics.