Li Jiemin, Xu Lei, Garcia-Fernandez Mirian, Nag Abhishek, Robarts H C, Walters A C, Liu X, Zhou Jianshi, Wohlfeld Krzysztof, van den Brink Jeroen, Ding Hong, Zhou Ke-Jin
Diamond Light Source, Harwell Campus, Didcot OX11 0DE, United Kingdom.
Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.
Phys Rev Lett. 2021 Mar 12;126(10):106401. doi: 10.1103/PhysRevLett.126.106401.
We explore the existence of the collective orbital excitations, orbitons, in the canonical orbital system KCuF_{3} using the Cu L_{3}-edge resonant inelastic x-ray scattering. We show that the nondispersive high-energy peaks result from the Cu^{2+} dd orbital excitations. These high-energy modes display good agreement with the ab initio quantum chemistry calculation, indicating that the dd excitations are highly localized. At the same time, the low-energy excitations present clear dispersion. They match extremely well with the two-spinon continuum following the comparison with Müller ansatz calculations. The localized dd excitations and the observation of the strongly dispersive magnetic excitations suggest that the orbiton dispersion is below the resolution detection limit. Our results can reconcile with the strong local Jahn-Teller effect in KCuF_{3}, which predominantly drives orbital ordering.
我们利用铜L₃边共振非弹性X射线散射，探索规范轨道系统KCuF₃中集体轨道激发（轨道子）的存在。我们表明，非色散高能峰源于Cu²⁺的dd轨道激发。这些高能模式与从头算量子化学计算结果吻合良好，表明dd激发是高度局域化的。同时，低能激发呈现出明显的色散。与米勒假设计算结果比较后发现，它们与双自旋子连续体极其匹配。局域化的dd激发以及强色散磁激发的观测表明，轨道子色散低于分辨率检测极限。我们的结果与KCuF₃中强烈的局域 Jahn-Teller 效应相符，该效应主要驱动轨道有序化。
