Electron-Lattice Interplays in LaMnO3 from Canonical Jahn-Teller Distortion Notations

TL;DR

This paper revisits LaMnO$_3$ using first-principles calculations, revealing its propensity for charge and orbital ordering driven by Jahn-Teller distortions, and reinterprets its metal-insulator transition as a Peierls transition influenced by spin fluctuations.

Contribution

It introduces canonical notations for lattice distortions in perovskites and demonstrates the role of tetragonal strain and spin fluctuations in LaMnO$_3$'s electronic phases.

Findings

Charge and orbital orderings are enabled by oxygen octahedra rotations.

Tetragonal strain influences the competition between different orders.

Metal-insulator transition is a Peierls transition facilitated by spin symmetry breaking.

Abstract

LaMnO$_3$ is considered as a prototypical Jahn-Teller perovskite compound, exhibiting a metal to insulator transition at $T_{JT} = 750K$ related to the joint appearance of an electronic orbital ordering and a large lattice Jahn-Teller distortion. From first-principles, we revisit the behavior of LaMnO$_3$ and show that it is not only prone to orbital ordering but also to charge ordering. Both charge and orbital orderings appear to be enabled by rotations of the oxygen octahedra and the subtle competition between them is monitored by a large tetragonal compressive strain, that is itself a Jahn-Teller active distortion. Equally, the competition of ferromagnetic and antiferromagnetic orders is slave of the same tetragonal strain. Our results further indicate that the metal to insulator transition can be thought as a Peierls transition that is enabled by spin symmetry breaking. Therefore, dynamical spin fluctuations in the paramagnetic state stabilize the insulating phase by the instantaneous symmetry breaking they produce and which is properly captured from static DFT calculations. As a basis to our discussion, we introduce canonical notations for lattice distortions in perovskites that distort the oxygen octhedra and are connected to charge and orbital orderings.