Resonant inelastic X-ray scattering as a probe of J_eff = 1/2 state in 3d transition-metal oxide

Hsiao-Yu Huang^1*, A. Singh¹, C. I. Wu², J. D. Xie³, J. Okamoto¹, A. A. Belik⁴, E. Kurmaev⁵, A. Fujimori^1,7, C. T. Chen¹, S. V. Streltsov^5,6, D. J. Huang^1,3,7

¹National Synchrotron Radiation Research Center, Hsinchu, Taiwan
²Graduate Program in Science and Technology of Synchrotron Light Source, National Tsing Hua University, Hsinchu, Taiwan
³Department of Electrophysics, National Yang Ming Chiao Tung University, Hsinchu, Taiwan
⁴International Center for Materials Nanoarchitectonics (WPI-MANA), National Institute for Materials Science (NIMS), Ibaraki, Japan
⁵Institute of Metal Physics, Ekaterinburg,, Russian Federation
⁶Department of theoretical physics and applied mathematics, Ural Federal University, Ekaterinburg, Russian Federation
⁷Department of Physics, National Tsing Hua University, Hsinchu, Taiwan

* Presenter:Hsiao-Yu Huang, email:huang.hy@nsrrc.org.tw

The state with effective total moment J_eff = 1/2 stabilized by the spin-orbit coupling is known to suppress Jahn-Teller distortions and may induce a strong exchange anisotropy. This in turn may lead to the formation of an elusive spin-liquid state in real materials. While recent studies have demonstrated that such a situation can be realized in 3d transition-metal compounds such as those based on Co²⁺ and Cu²⁺, diagnosis of J_eff = 1/2 state remains challenging. We show that resonant inelastic X-ray scattering is an effective tool to probe this state and apply it to CuAl₂O₄, materials where Cu²⁺ ions were previously proposed to be in the J_eff = 1/2 state. Our results unambiguously demonstrate that, contrary to previous expectations, a competitive (to J_eff = 1/2) Jahn-Teller state realizes in this compound.

Keywords: spin-orbit coupling, Jahn-Teller distortion, resonant inelastic X-ray scattering