Pseudo Jahn-Teller Effect and Magnetoelastic Coupling in Spin-Orbit Mott Insulators

TL;DR

This paper investigates how pseudo-Jahn-Teller effects influence magnetism and orbital order in spin-orbit Mott insulators, explaining phenomena in Sr2IrO4 and Ca2RuO4 through a unified theoretical framework.

Contribution

It introduces a theory linking pseudo-Jahn-Teller effects to magnetic and orbital phenomena in J_eff=1/2 and J_eff=0 compounds, resolving existing puzzles.

Findings

Pseudo-Jahn-Teller effect causes orthorhombic distortions in Sr2IrO4.

The theory explains magnetic anisotropy and magnon gaps in Sr2IrO4.

Pseudo-Jahn-Teller effect induces spin-nematic transition in Ca2RuO4.

Abstract

The consequences of the Jahn-Teller (JT) orbital-lattice coupling for magnetism of pseudospin J_{eff}=1/2 and J_{eff}=0 compounds are addressed. In the former case, represented by Sr_2IrO_4, this coupling generates, through the so-called pseudo-JT effect, orthorhombic deformations of a crystal concomitant with magnetic ordering. The orthorhombicity axis is tied to the magnetization and rotates with it under magnetic field. The theory resolves a number of puzzles in Sr_2IrO_4 such as the origin of in-plane magnetic anisotropy and magnon gaps, metamagnetic transition, etc. In J_{eff}=0 systems, the pseudo-JT effect leads to spin-nematic transition well above magnetic ordering, which may explain the origin of `orbital order' in Ca_2RuO_4