# Relation between Kitaev magnetism and structure in $\alpha$-RuCl$_3$

## TL;DR

This study uses Raman scattering to explore how structural phases in $eta$-RuCl$_3$ influence its magnetic excitations, revealing a strong coupling between lattice structure and Kitaev magnetic behavior.

## Contribution

It provides new insights into how structural transitions affect Kitaev magnetism and fractionalized excitations in $eta$-RuCl$_3$.

## Key findings

- Structural transition from monoclinic to rhombohedral detected
- Large thermal hysteresis observed in $eta$-RuCl$_3$
- Magnetic excitations are sensitive to structural phases

## Abstract

Raman scattering has been employed to investigate lattice and magnetic excitations of the honeycomb Kitaev material $\alpha$-RuCl$_3$ and its Heisenberg counterpart CrCl$_3$. Our phonon Raman spectra give evidence for a first-order structural transition from a monoclinic to a rhombohedral structure for both compounds. Significantly, only $\alpha$-RuCl$_3$ features a large thermal hysteresis, consistent with the formation of a wide phase of coexistence. In the related temperature interval of $70-170$ K, we observe a hysteretic behavior of magnetic excitations as well. The stronger magnetic response in the rhombohedral compared to the monoclinic phase evidences a coupling between the crystallographic structure and low-energy magnetic response. Our results demonstrate that the Kitaev magnetism concomitant with fractionalized excitations is susceptible to small variations of bonding geometry.