Shilong Zhang, H. H. Zhang, Zehao Dong, Jie Li, Xiao Ming Qian, Mengwu Huo, H. Y. Huang, D. J. Huang, Yayu Wang, Yi Lu, Zhen Chen, Meng Wang, Yingying Peng
High- T c superconductivity has recently been discovered in Ruddlesden-Popper (RP)-phase nickelates under pressure, where the low-energy electronic structure is dominated by Ni d x 2 − y 2 and d z 2 orbitals. However, the respective roles of these orbitals in superconductivity remain unclear. Here, by combining x-ray absorption, electron energy loss spectroscopy, and density functional theory calculations on La 4 Ni 3 O 10 single crystals, we identify ligand holes in the p x , y orbitals of planar oxygen and the p z orbitals of apical oxygen, which hybridize with the Ni d x 2 − y 2 and d z 2 orbitals, respectively. These ligand holes enable orbital-selective O K -edge resonant inelastic x-ray scattering (RIXS) study, which reveals that d x 2 − y 2 states dominate the low-energy charge excitations and are more itinerant. We also observe an ∼ 0.1 eV bimagnon through RIXS and Raman spectroscopy. Our results reveal distinct contributions of Ni d x 2 − y 2 and d z 2 orbitals to the electronic and magnetic structure and provide direct experimental insights to understand the RP-phase nickelate superconductors.