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 ${\mathrm{Ca}}_2{\mathrm{RuO}}_4$ 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 ${\mathrm{K}}_2{\mathrm{RuCl}}_6$, 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.

中文翻译：

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K2RuCl6 中的非磁性 J=0 状态和自旋轨道激发

自旋轨道莫特绝缘体由 ${吨}_{2G}^4$ 由于自旋轨道的凝聚，过渡金属离子可能具有激子磁性 $J=1$三联体。之前的实验表明，$4d$ 反铁磁体 ${钙}_2{\mathrm{氧化钌}}_4$ 体现了这一理念，但 $J=0$作为激子图像基础的非磁性状态仍有待证实。我们用茹${升}_3$-边缘共振非弹性 X 射线散射揭示原型 $J$ 多重峰 $J=0$ 立方化合物中的基态 ${\mathrm{钾}}_2{\mathrm{氯化钌}}_6$，这在 $升秒$-耦合方案。该结果强调了未淬灭的轨道矩在$4d$- 电子化合物，并呼吁研究各种晶格上的量子临界性和激子磁性。