The d5 electron configurations under the crystal field, spin–orbit coupling, and Coulomb interaction give rise to a plethora of profound ground states. Ruthenium perovskite oxides exhibit a number of unconventional properties yet the Ru4+ state (4d4) is usually stable in these materials. In this regard, Ru3+ ions in perovskite materials are expected to be a mesmerizing playground of 4d5 electron configurations. Here, we report measurements of x-ray photoemission spectroscopy on recently synthesized perovskite ruthenium oxide thin films, LaRuO3 and NdRuO3, whose valence state of the ruthenium ions is trivalent. We discuss correlation and spin–orbit effects from the valence band spectra, in particular an additional peak structure around 3–5 eV, reminiscent of the so-called 3 eV peak observed in Sr2RuO4. Moreover, we find that the core-level spectra of these materials are quantitatively different from those in other ruthenates, which possess Ru4+ ions, e.g., SrRuO3. We therefore argue that the core level spectra of LaRuO3 and NdRuO3 are peculiar to the Ru3+ states.

中文翻译：

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钌钙钛矿氧化物薄膜中三价钌离子的光谱研究


晶体场、自旋轨道耦合和库仑相互作用下的 d5 电子构型产生了大量深刻的基态。钌钙钛矿氧化物表现出许多非常规特性，但 Ru4+ 态 (4d4) 在这些材料中通常是稳定的。在这方面，钙钛矿材料中的 Ru3+ 离子有望成为 4d5 电子构型的一个令人着迷的游乐场。在这里，我们报告了最近合成的钙钛矿氧化钌薄膜 LaRuO3 和 NdRuO3 的 X 射线光电子能谱测量，其钌离子的价态为三价。我们讨论了价带光谱的相关性和自旋轨道效应，特别是 3-5 eV 附近的附加峰结构，让人想起在 Sr2RuO4 中观察到的所谓 3 eV 峰。此外，我们发现这些材料的核心能级光谱与其他含有 Ru4+ 离子（例如 SrRuO3）的钌酸盐存在定量差异。因此，我们认为 LaRuO3 和 NdRuO3 的核心能级光谱是 Ru3+ 态所特有的。