Chiral spin-order in some purported Kitaev spin-liquid compounds

TL;DR

This paper investigates magnetic torque measurements in $ ext{Li}_2 ext{IrO}_3$ and $ ext{RuCl}_3$, revealing evidence of chiral spin-order that challenges the conventional understanding of Kitaev spin liquids and suggests new topological phenomena.

Contribution

It proposes the existence of a translationally-invariant chiral spin-order in these compounds, supported by torque data analysis and theoretical predictions of unique magnetic field dependencies.

Findings

Evidence of chiral spin-order in the compounds.

Prediction of an $|B|B^2$ torque dependence at low fields.

Consistency of the predicted torque behavior with experimental data.

Abstract

We examine recent magnetic torque measurements in two compounds, $\gamma$-Li$_2$IrO$_3$ and RuCl$_3$, which have been discussed as possible realizations of the Kitaev model. The analysis of the reported discontinuity in torque, as an external magnetic field is rotated across the $c-$axis in both crystals, suggests that they have a translationally-invariant chiral spin-order of the from $<{\bf S}_i. ({\bf S}_j ~\times ~ {\bf S}_k)> \ne 0$ in the ground state and persisting over a very wide range of magnetic field and temperature. An extra-ordinary $|B|B^2$ dependence of the torque for small fields, beside the usual $B^2$ part, is predicted due to the chiral spin-order, and found to be consistent with experiments upon further analysis of the data. Other experiments such as inelastic scattering and thermal Hall effect and several questions raised by the discovery of chiral spin-order, including its topological consequences are discussed.