Insulating band gaps both below and above the N\'eel temperature in d-electron LaTiO3, LaVO3, SrMnO3, and LaMnO3 perovskites as a symmetry-breaking event

TL;DR

This study investigates how intrinsic structural and magnetic symmetry breaking in ABO3 perovskites can explain insulating band gaps both below and above the Nél temperature, challenging traditional correlation-based explanations.

Contribution

It demonstrates that local symmetry-breaking motifs can systematically account for insulating behavior across magnetic transitions in certain perovskites, offering a new perspective beyond electron correlation effects.

Findings

Intrinsic symmetry breaking explains insulating gaps both below and above T_N.

Local structural and magnetic motifs are key to understanding band gaps.

Some compounds like SrVO3 do not follow this pattern, indicating exceptions.

Abstract

Compounds having an odd number of electrons with the same orbital character in occupied and unoccupied band edge states would be expected to have band degeneracy at the Fermi energy, making such reference system metals. Yet, many ABO3 oxide perovskites with a magnetic 3d B-atom are, in fact, insulators both below and above the Neel temperature. These inconsistencies between experimental observation and expectation have been traditionally resolved by invoking degeneracy-breaking physics based largely on high-order electron effects, such as strong interelectronic correlation (the Mott mechanism). Such explanations generally utilize the highest symmetry structure, considering microscopic degrees of freedom (m-DOF) as largely passive spectators. Yet, it has long been known that ABO3 perovskites can manifest an arrangement of m-DOFs in the form of octahedral tilting, bond dimerization, Jahn-Teller distortions, and ordering of local magnetic moments as part of the stabilizing intrinsic symmetry. Such m-DOFs are seen both by local experimental probes and theoretically in total energy minimization of its Born-Oppenheimer state. While such local structural and magnetic symmetry breaking motifs were often considered to be the reason for gapping of the reference system below the transition into Para phases, it was also often thought that above the transition those local motifs might vanish, requiring a different mechanism for gapping - such as strong correlation. Here we examine if such intrinsic structural and magnetic symmetry breaking might systematically explain the formation of insulating band gaps both below and above the magnetic transition and account at the same time for specific and non-accidental exceptions of the absence of gaping in some compounds, such as SrVO3.