Coulomb Correlations in 4d and 5d Oxides from First Principles - or How Spin-Orbit Materials choose their Effective Orbital Degeneracies

TL;DR

This paper reviews recent first-principles studies on how spin-orbit coupling and Coulomb interactions influence the effective orbital degeneracies in 4d and 5d oxides, affecting their electronic phases.

Contribution

It introduces the concept of effective degeneracy as a key factor in understanding phase diagrams of spin-orbit coupled materials, based on dynamical mean-field theory calculations.

Findings

Effective degeneracy varies with spin-orbit strength and Coulomb interactions.

The phase behavior of iridates and rhodates is governed by this degeneracy.

First-principles methods elucidate the role of orbital degeneracies in these materials.

Abstract

The interplay of spin-orbit interactions and Coulomb correlations has become a hot topic in condensed matter theory. Here, we review recent advances in dynamical mean-field theory-based electronic structure calculations for iridates and rhodates. We stress the notion of the effective degeneracy of the compounds, which introduces an additional axis into the conventional picture of a phase diagram based on filling and on the ratio of interactions to bandwidth.