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arXiv · 2005.08200

Spin-orbital liquid in Ba$_3$CuSb$_2$O$_9$ stabilized by oxygen holes

Kou Takubo·Takashi Mizokawa·Huiyuan Man·Kohei Yamamoto·Yujun Zhang·Yasuyuki Hirata·Hiroki Wadati·Akira Yasui·Daniel I. Khomskii·Satoru Nakatsuji
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Abstract

Both the Jahn-Teller distortion of Cu$^{2+}$O$_6$ octahedra and magnetic ordering are absent in hexagonal Ba$_3$CuSb$_2$O$_9$ suggesting a Cu 3$d$ spin-orbital liquid state. Here, by means of resonant x-ray scattering and absorption experiment, we show that oxygen 2$p$ holes play crucial role in stabilizing this spin-orbital liquid state. These oxygen holes appear due to the "reaction" Sb$^{5+}$$\rightarrow$Sb$^{3+}$ $+$ two oxygen holes, with these holes being able to attach to Cu ions. The hexagonal phase with oxygen 2$p$ holes exhibits also a novel charge-orbital dynamics which is absent in the orthorhombic phase of Ba$_3$CuSb$_2$O$_9$ with Jahn-Teller distortion and Cu 3$d$ orbital order. The present work opens up a new avenue towards spin-charge-orbital entangled liquid state in transition-metal oxides with small or negative charge transfer energy.

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Kou Takubo, Takashi Mizokawa, Huiyuan Man, Kohei Yamamoto, Yujun Zhang, Yasuyuki Hirata, Hiroki Wadati, Akira Yasui, Daniel I. Khomskii, Satoru Nakatsuji. 2020-05-17. Spin-orbital liquid in Ba$_3$CuSb$_2$O$_9$ stabilized by oxygen holes. https://doi.org/10.1103/physrevmaterials.5.075002

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