Nonmagnetic $J = 0$ State and Spin-Orbit Excitations in K$_{2}$RuCl$_{6}$

TL;DR

This study confirms a nonmagnetic J=0 ground state in K$_{2}$RuCl$_{6}$ using resonant inelastic x-ray scattering, emphasizing the importance of unquenched orbital moments in 4d-electron compounds and opening avenues for exploring excitonic magnetism.

Contribution

First experimental confirmation of a J=0 nonmagnetic ground state in K$_{2}$RuCl$_{6}$, supporting the excitonic magnetism framework in 4d transition metal compounds.

Findings

Identified J multiplets with a J=0 ground state in K$_{2}$RuCl$_{6}$

Demonstrated the relevance of unquenched orbital moments in 4d systems

Supported the excitonic magnetism model in spin-orbit Mott insulators

Abstract

Spin-orbit Mott insulators composed of $t_{2g}^4$ transition metal ions may host excitonic magnetism due to the condensation of spin-orbital $J=1$ triplons. Prior experiments suggest that the $4d$ antiferromagnet Ca$_{2}$RuO$_{4}$ embodies this notion, but a $J = 0$ nonmagnetic state as a basis of the excitonic picture remains to be confirmed. We use Ru $L_3$-edge resonant inelastic x-ray scattering to reveal archetypal $J$ multiplets with a $J=0$ ground state in the cubic compound K$_{2}$RuCl$_{6}$, which are well described within the $LS$-coupling scheme. This result highlights the critical role of unquenched orbital moments in $4d$-electron compounds and calls for investigations of quantum criticality and excitonic magnetism on various crystal lattices.