- Hepting, M;
- Li, D;
- Jia, CJ;
- Lu, H;
- Paris, E;
- Tseng, Y;
- Feng, X;
- Osada, M;
- Been, E;
- Hikita, Y;
- Chuang, Y-D;
- Hussain, Z;
- Zhou, KJ;
- Nag, A;
- Garcia-Fernandez, M;
- Rossi, M;
- Huang, HY;
- Huang, DJ;
- Shen, ZX;
- Schmitt, T;
- Hwang, HY;
- Moritz, B;
- Zaanen, J;
- Devereaux, TP;
- Lee, WS
The search continues for nickel oxide-based materials with electronic properties similar to cuprate high-temperature superconductors1-10. The recent discovery of superconductivity in the doped infinite-layer nickelate NdNiO2 (refs. 11,12) has strengthened these efforts. Here, we use X-ray spectroscopy and density functional theory to show that the electronic structure of LaNiO2 and NdNiO2, while similar to the cuprates, includes significant distinctions. Unlike cuprates, the rare-earth spacer layer in the infinite-layer nickelate supports a weakly interacting three-dimensional 5d metallic state, which hybridizes with a quasi-two-dimensional, strongly correlated state with [Formula: see text] symmetry in the NiO2 layers. Thus, the infinite-layer nickelate can be regarded as a sibling of the rare-earth intermetallics13-15, which are well known for heavy fermion behaviour, where the NiO2 correlated layers play an analogous role to the 4f states in rare-earth heavy fermion compounds. This Kondo- or Anderson-lattice-like 'oxide-intermetallic' replaces the Mott insulator as the reference state from which superconductivity emerges upon doping.