Mott insulators with spin-orbit entangled 𝑗=1/2 moments host intriguing magnetic properties. The 𝑗=1/2 wave function requires cubic symmetry, while a noncubic crystal field mixes 𝑗=1/2 and 3/2 character. Spectroscopic studies of 5⁢𝑑5 iridates typically claim noncubic symmetry, e.g., based on a splitting of the excited 𝑗=3/2 quartet. A sizable splitting is particularly puzzling in antifluorite-type K2⁢IrCl6, a frustrated fcc quantum magnet with global cubic symmetry. It raises the fundamental question about the stability of 𝑗=1/2 moments against magnetoelastic coupling. Combining resonant inelastic x-ray scattering with optical spectroscopy, we demonstrate that the multi-peak line shape in K2⁢IrCl6 reflects a vibronic character of the 𝑗=3/2 states rather than a noncubic crystal field. The quasimolecular crystal structure with well separated IrCl6 octahedra explains the existence of well-defined sidebands that are usually smeared out in solids. Our results highlight the spin orbital lattice entangled character of cubic K2⁢IrCl6 with ideal 𝑗=1/2 moments.

中文翻译：

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理想中的自旋轨道晶格纠缠j=12化合物K2IrCl6


具有自旋轨道纠缠 j=1/2 矩的 Mott 绝缘体具有有趣的磁性。j=1/2 波函数需要三次对称性，而非三次晶体场混合了 j=1/2 和 3/2 字符。5d5 虹膜的光谱研究通常声称非三次对称性，例如，基于激发的 j=3/2 四重体的分裂。在反萤石型 K2IrCl6 中，相当大的分裂尤其令人费解，这是一种具有全局立方对称性的受挫 fcc 量子磁体。它提出了一个基本问题，即 j=1/2 矩对磁弹性耦合的稳定性。将共振非弹性 X 射线散射与光谱相结合，我们证明了 K2IrCl6 中的多峰线形状反映了 j=3/2 态的振动特性，而不是非立方晶场。具有良好分离的 IrCl6 八面体的准分子晶体结构解释了通常在固体中涂抹的明确边带的存在。我们的结果突出了具有理想 j=1/2 矩的立方 K2IrCl6 的自旋轨道晶格纠缠特性。