Correlated quantum phenomena in the strong spin-orbit regime

TL;DR

This paper explores how strong spin-orbit coupling and electron correlations in heavy transition metal compounds lead to diverse quantum phases, including topological insulators, Weyl semimetals, and quantum spin liquids, with implications for future materials research.

Contribution

It provides a comprehensive analysis of emergent quantum phenomena driven by spin-orbit entanglement in 4d and 5d transition metal compounds, highlighting novel phases and their experimental relevance.

Findings

Identification of topological phases in pyrochlore iridates.

Prediction of Weyl semimetals and axion insulators.

Enhanced quantum fluctuations in spin-orbital entangled states.

Abstract

We discuss phenomena arising from the combined influence of electron correlation and spin-orbit coupling, with an emphasis on emergent quantum phases and transitions in heavy transition metal compounds with 4d and 5d elements. A common theme is the influence of spin-orbital entanglement produced by spin-orbit coupling, which influences the electronic and magnetic structure. In the weak-to-intermediate correlation regime, we show how non-trivial band-like topology leads to a plethora of phases related to topological insulators. We expound these ideas using the example of pyrochlore iridates, showing how many novel phases such as the Weyl semi-metal, axion insulator, topological Mott insulator, and topological insulators may arise in this context. In the strong correlation regime, we argue that spin-orbital entanglement fully or partially removes orbital degeneracy, reducing or avoiding the normally ubiquitous Jahn-Teller effect. As we illustrate for the honeycomb lattice iridates and double perovskites, this leads to enhanced quantum fluctuations of the spin-orbital entangled states and the chance to promote exotic quantum spin liquid and multipolar ordered ground states. Connections to experiments, materials, and future directions are discussed.