# Antiferromagnetic Kitaev Interactions in Polar Spin-Orbit Mott Insulators

## TL;DR

This paper proposes a new mechanism for inducing dominant antiferromagnetic Kitaev interactions in polar spin-orbit Mott insulators, supported by ab initio calculations on specific ruthenium halide compounds, expanding the potential for quantum spin liquid realization.

## Contribution

It introduces a polar structural asymmetry approach to activate antiferromagnetic Kitaev interactions, contrasting with conventional ferromagnetic interactions, and demonstrates this in ruthenium halide materials.

## Key findings

- Polar asymmetry activates antiferromagnetic Kitaev interactions.
- Ab initio calculations show large antiferromagnetic interactions in Ru trihalides.
- Potential to realize Kitaev spin liquids in new material classes.

## Abstract

A bond-directional anisotropic exchange interaction, called the Kitaev interaction, is a promising route to realize quantum spin liquids. The Kitaev interactions were found in Mott insulators with the strong spin-orbit coupling, in the presence of quantum interference between indirect electron transfers. Here we theoretically propose a different scenario by introducing a polar structural asymmetry that unbalances the quantum interference. We show that the imbalance activates additional exchange processes and gives rise to a dominant antiferromagnetic Kitaev interaction, in stark contrast to the conventional ferromagnetic ones. We demonstrate by ab initio calculations that polar Ru trihalides with multiple anions, $\alpha$-RuH$_{3/2}X_{3/2}$ ($X$=Cl and Br), exhibit the antiferromagnetic Kitaev interaction whose magnitude is several times larger compared to existing candidates. Our proposal opens the way for materializing the Kitaev spin liquids in unexplored parameter regions.