Spin state evolution induced by hole doping in La2-xSrxCoO₄
Jun Okamoto1*, Ashish Chainani1, Zhi-Ying Chen2, Hsiao-Yu Huang1, Amol Singh1, Wen-Bin Wu1, Takao Sasagawa3, Chien-Te Chen1, Di-Jing Huang1,2
1National Synchrotron Radiation Research Center, Hsinchu, Taiwan
2Department of Physics, National Tsing Hua University, Hsinchu, Taiwan
3Materials and Structures Laboratory, Tokyo Institute of Technology, Yokohama, Kanagawa, Japan
* Presenter:Jun Okamoto, email:okamoto.jun@nsrrc.org.tw
K2NiF4-type antiferromagnetic Mott insulators La2TMO4 (TM = 3d transition metal) show various novel physical properties by doping holes, like high TC superconductivity [1]. La2-xSrxCoO4 shows checkerboard-type charge ordering of Co2+ and Co3+ ions in 1/3 < x ≤ 0.6 and incommensurate antiferromagnetic ordering controlled by antiferromagnetic exchange interaction between Co2+ high spin (HS) in 1/3 < x ≤ 0.9 [2]. As doping holes in La2-xSrxCoO4, Co2+ HS is replaced by Co3+, but Co3+ may take low-spin (LS) or HS states. Information about Co3+ spin state with hole doping is important to understand the phase diagram of charge and magnetic ordering in La2-xSrxCoO4. We have measured Co L3-edge resonant inelastic X-ray scattering (RIXS) of La2-xSrxCoO4 (x =0.5, 0.7, and 0.8) to investigate the change of local electronic structures of Co2+ and Co3+ with different hole-doping. We have anlyzed changes of RIXS structures originated from Co2+ HS and Co3+ LS states as Sr doping increases from 0.5 to 0.8, and revealed that splitting of t2g orbitals of Co3+ increases while that of Co2+ decreases, and HS ratio in Co3+ increases at the same time. This result means that Co3+ spin-state evolution is induced by hole doping through the increase of t2g splitting in Co3+ electronic structure.

[1]: J. G. Bednorz and K. A. Müller, Z. Phys. B 64, 189 (1986). 
[2]: Z. Li et al., Sci, Rep. 6, 25117 (2016)

Keywords: strongly correlated electron systems, Resonant Inelasitc X-ray Scattering, Cobaltates, Spin state