摘要
We present x-ray spectral evidence for the evolution of valence- and spin-specific tetragonal distortions in single-layer cobaltates. Measurements of Co ?3-edge resonant inelastic x-ray scattering reveal the ?2? electronic structure of Co in hole-doped La2−?Sr?CoO4 (?=0.5, 0.7, and 0.8). As the Sr-doping ? increases, the tetragonal splitting of the ?2? states of high-spin Co2+ decreases, whereas that of low-spin Co3+ increases and the population fraction of high-spin Co3+ increases. The results enable us to clarify the origin of the change of magnetic anisotropy and in-plane resistivity in the mixed-valence cobaltates caused by the interplay of spin-orbit coupling and tetragonal distortion.