A study of a dd excitation in La4<\sub>Ni3<\sub>O8<\sub> (La-438) using x-ray absorption scattering (XAS) and resonant inelastic x-ray scattering (RIXS) at the Ni K-edge is presented. The incident energy dependence of this dd excitation shows a maximum at the 1s→4pπ<\sub> transition. Its intensity at the main edge is proportional to the amount of incident x-ray polarization parallel to the c-axis. These observations suggest that the RIXS process underlying this excitation includes a strong Ni 3d-Ni 4p Coulomb interaction and excludes the "4p-as-spectator" approximation. The dominant Ni 3d Coulomb interaction is with Ni 4pπ<\sub> with limited or no interaction with the Ni 4pσ<\sub>. An insulating gap closing is observed as a function of temperature.

中文翻译：

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方形平面 La4Ni3O8 中的电子耦合

使用 X 射线吸收散射 (XAS) 和共振非弹性 X 射线散射 (RIXS) 在 Ni K 处研究 La4<\sub>Ni3<\sub>O8<\sub> (La-438) 中的 dd 激发-edge 出现。这种 dd 激发的入射能量依赖性在 1s→4pπ<\sub> 跃迁处显示出最大值。它在主边缘的强度与平行于 c 轴的入射 x 射线偏振量成正比。这些观察结果表明，这种激发背后的 RIXS 过程包括强烈的 Ni 3d-Ni 4p 库仑相互作用，并且排除了“4p 作为旁观者”的近似。主要的 Ni 3d Coulomb 相互作用是与 Ni 4pπ<\sub> 的相互作用，与 Ni 4pσ<\sub> 的相互作用有限或没有。观察到绝缘间隙闭合是温度的函数。