# Electronically highly cubic conditions for Ru in alpha-RuCl3

## TL;DR

This study reveals that alpha-RuCl3 exhibits highly cubic local symmetry in Ru 4d orbitals with negligible trigonal splitting, supporting its suitability for Kitaev physics due to its Jeff=1/2 ground state.

## Contribution

The paper demonstrates that Ru in alpha-RuCl3 has nearly perfect cubic symmetry and a Jeff=1/2 state, confirmed by spectroscopy and calculations, clarifying its electronic structure.

## Key findings

- Ru 4d orbitals are highly cubic with negligible trigonal splitting.
- The ratio of orbital to spin moments is 2.0, consistent with Jeff=1/2.
- Alpha-RuCl3 is an ideal candidate for Kitaev physics studies.

## Abstract

We studied the local Ru 4d electronic structure of alpha-RuCl3 by means of polarization dependent x-ray absorption spectroscopy at the Ru-L2,3 edges. We observed a vanishingly small linear dichroism indicating that electronically the Ru 4d local symmetry is highly cubic. Using full multiplet cluster calculations we were able to reproduce the spectra excellently and to extract that the trigonal splitting of the t2g orbitals is -12 $\pm10$ meV, i.e. negligible as compared to the Ru 4d spin-orbit coupling constant. Consistent with our magnetic circular dichroism measurements, we found that the ratio of the orbital and spin moments is 2.0, the value expected for a Jeff = 1/2 ground state. We have thus shown that as far as the Ru 4d local properties are concerned, alpha-RuCl3 is an ideal candidate for the realization of Kitaev physics.