The Challenge of Spin-Orbit-Tuned Ground States in Iridates

TL;DR

This review discusses the complex effects of spin-orbit interactions in iridates, highlighting their unique quantum states, experimental anomalies, and the challenges in reconciling experimental results with theoretical models.

Contribution

It provides a comprehensive survey of current experimental findings on iridates and emphasizes the need for further research to understand their unconventional properties.

Findings

Iridates exhibit unconventional magnetic and insulating behaviors.

Discrepancies exist between experimental results and theoretical predictions.

Unique physical properties may enable novel functional materials.

Abstract

Effects of spin-orbit interactions in condensed matter are an important and rapidly evolving topic. Strong competition between spin-orbit, on-site Coulomb and crystalline electric field interactions in iridates drives exotic quantum states that are unique to this group of materials. In particular, the Jeff = 1/2 Mott state served as an early signal that the combined effect of strong spin-orbit and Coulomb interactions in iridates has unique, intriguing consequences. In this Key Issues Review, we survey some current experimental studies of iridates. In essence, these materials tend to defy conventional wisdom: absence of conventional correlations between magnetic and insulating states, avoidance of metallization at high pressures, S-shaped I-V characteristic, emergence of an odd-parity hidden order, etc. It is particularly intriguing that there exist conspicuous discrepancies between current experimental results and theoretical proposals that address superconducting, topological and quantum spin liquid phases. This class of materials, in which the lattice degrees of freedom play a critical role seldom seen in other materials, evidently presents some profound intellectual challenges that call for more investigations both experimentally and theoretically. Physical properties unique to these materials may help unlock a world of possibilities for functional materials and devices. We emphasize that, given the rapidly developing nature of this field, this Key Issues Review is by no means an exhaustive report of the current state of experimental studies of iridates.