Scattering Continuum and Possible Fractionalized Excitations in $\alpha$-RuCl$_3$

TL;DR

This study uses Raman scattering to reveal a broad magnetic continuum in $ ext{RuCl}_3$, indicating frustrated magnetic interactions and potential proximity to a quantum spin liquid state due to unconventional excitations.

Contribution

It provides experimental evidence of magnetic continua and spin-phonon coupling in $ ext{RuCl}_3$, supporting its proximity to a quantum spin liquid phase as predicted by the Heisenberg-Kitaev model.

Findings

Observation of a broad magnetic continuum in Raman spectra.

Temperature dependence suggests frustrated magnetic interactions.

Anomalies in phonon linewidths indicate spin-phonon coupling.

Abstract

The combination of electronic correlation and spin-orbit coupling is thought to precipitate a variety of highly unusual electronic phases in solids, including topological and quantum spin liquid states. We report a Raman scattering study that provides evidence for unconventional excitations in $\alpha$-RuCl$_3$, a spin-orbit coupled Mott insulator on the honeycomb lattice. In particular, our measurements reveal unusual magnetic scattering, typified by a broad continuum. The temperature dependence of this continuum is evident over a large scale compared to the magnetic ordering temperature, suggestive of frustrated magnetic interactions. This is confirmed through an analysis of the phonon linewidths, which show a related anomaly due to spin-phonon coupling. These observations are in line with theoretical expectations for the Heisenberg-Kitaev model and suggest that $\alpha$-RuCl$_3$ may be close to a quantum spin liquid ground state.