Detuning the Honeycomb of $\alpha$-RuCl$_{3}$: Pressure-Dependent Optical Studies Reveal Broken Symmetry

TL;DR

This study uses optical spectroscopy and computational methods to investigate how pressure induces structural and electronic changes in $ ext{RuCl}_3$, revealing a broken symmetry phase that precludes a pressure-induced Kitaev quantum spin liquid.

Contribution

It provides new insights into pressure-induced structural transitions and electronic property changes in $ ext{RuCl}_3$, challenging previous expectations of quantum spin liquid formation under pressure.

Findings

Identification of a dimerized structure above 1 GPa

Breakdown of the relativistic $j_{eff}$ picture under pressure

Pressure prevents the formation of a Kitaev quantum spin liquid

Abstract

The honeycomb Mott insulator $\alpha$-RuCl$_3$ loses its low-temperature magnetic order by pressure. We report clear evidence for a dimerized structure at $P>1$ GPa and observe the breakdown of the relativistic $j_{\rm eff}$ picture in this regime strongly affecting the electronic properties. A pressure-induced Kitaev quantum spin liquid cannot occur in this broken symmetry state. We shed light on the new phase by broad-band infrared spectroscopy of the low-temperature properties of $\alpha$-RuCl$_{3}$ and ab initio density functional theory calculations, both under hydrostatic pressure.