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# Electronic structure of the parent compound of superconducting infinite-layer nickelates

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A Publisher Correction to this article was published on 13 July 2020

## Abstract

The search continues for nickel oxide-based materials with electronic properties similar to cuprate high-temperature superconductors1,2,3,4,5,6,7,8,9,10. 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 $$3d_{x^2-y^2}$$ symmetry in the NiO2 layers. Thus, the infinite-layer nickelate can be regarded as a sibling of the rare-earth intermetallics13,14,15, 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.

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## Data availability

Raw data are shown in Figs. 1a–d and 2a–e, Extended Data Fig. 1 and Extended Data Fig. 2. The data that support the plots within this paper and other findings of this study are available from the corresponding authors upon reasonable request.

## Code availability

QUANTUM ESPRESSO and Wannier90 are freely available at https://www.quantum-espresso.org and http://www.wannier.org, respectively. Access to RIXS exact diagonalization and Python analysis codes will be accommodated upon reasonable request to the corresponding authors.

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## Acknowledgements

We thank G.A. Sawatzky and E. Benckiser for discussions. This work is supported by the US Department of Energy (DOE), Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division, under contract no. DE-AC02-76SF00515. X.F. and D.L. acknowledge partial support from the Gordon and Betty Moore Foundation’s EPiQS Initiative through grant no. GBMF4415. Part of the synchrotron experiments were performed at the ADRESS beamline of the Swiss Light Source (SLS) at the Paul Scherrer Institut (PSI). The work at PSI is supported by the Swiss National Science Foundation through the NCCR MARVEL (research grant no. 51NF40_141828) and the Sinergia network Mott Physics Beyond the Heisenberg Model—MPBH (research grant no. CRSII2_160765/1). Part of the research was conducted at the Advanced Light Source (ALS), which is a DOE Office of Science User Facility, under contract no. DE-AC02-05CH11231. We acknowledge preliminary XAS characterization at BL13-3, SSRL by J.S. Lee in the early stage of the project.

## Author information

Authors

### Contributions

W.S.L., M.H. and H.Y. Hwang conceived the experiment. M.H., H.L., E.P., Y.T., T.S. and W.S.L. conducted the experiment at SLS. H.L., W.S.L., Z.H. and Y.-D.C. conducted the experiment at ALS. H.L., W.S.L., A.N. and K.J.Z. conducted XAS measurement at Diamond Light Source. M.R., W.S.L., H.Y. Huang and D.J.H. conducted XAS measurements at NSRRC. J.S.L. contributed to XAS characterization of samples at an early stage of the work. M.H., H.L. and W.S.L. analysed the data. C.J.J., B.M., J.Z. and T.P.D. performed the theoretical calculations. D.L., X.F., Y.H., M.O. and H.Y. Hwang synthesized and characterized the nickelate samples using transport and XRD. M.H., Z.X.S. and W.S.L. prepared and aligned samples for X-ray spectroscopy measurements. M.H., B.M., J.Z. and W.S.L. wrote the manuscript with input from all authors.

### Corresponding authors

Correspondence to C. J. Jia or W. S. Lee.

## Ethics declarations

### Competing interests

The authors declare no competing interests.

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## Extended data

### Extended Data Fig. 1 XRD characterization and electrical transport measurements.

a, XRD pattern of the LaNiO3, LaNiO2.5, and LaNiO2 films grown on SrTiO3 (001) substrates, measured with Cu Kα radiation. The red arrows indicate the nickelate film peaks and the black arrow the (002) SrTiO3 substrate peak. The film peak shifts to higher 2θ values as a function of apical oxygen reduction. The curves are offset in vertical direction for clarity. b, Resistivity vs. temperature of the LaNiO3 and LaNiO2 film.

### Extended Data Fig. 2 Ni L-edge, La M4-edge and Nd M5-edge x-ray absorption spectra (XAS).

a, XAS of LaNiO3 and LaNiO2 across the Ni L3,2-edge before subtraction of the La M4 absorption peak. The XAS of NiO powder is also shown. Spectra are offset in vertical direction for clarity. b, XAS of NdNiO3 and NdNiO2 across the Nd M5-edge. The XAS were taken using total fluorescence yield. The XAS spectra across the rare-earth M-edges of the La- and Nd-based infinite-layer nickelates are essentially identical to those of their perovskite counterparts (LaNiO3 and NdNiO3). This implies a similar configuration of 4f states for both types of nickelates and that the 4f states of La3+ and Nd3+ do not hybridize in any significant way with the Ni 3d states.

### Extended Data Fig. 3 RIXS maps across the La M4-edge.

RIXS maps for (left) LaNiO2 and (right) LaNiO3 with incident photon energies including the La M4 edge. No orbital excitations exist in the inelastic channel of the RIXS spectra. This is consistent with a nominally empty 4f shell of the La3+ ion, implying that the 4f states are far from near-EF states and not hybridized with the Ni 3d states.

## Supplementary information

### Supplementary Information

Supplementary Tables 1–3.

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Hepting, M., Li, D., Jia, C.J. et al. Electronic structure of the parent compound of superconducting infinite-layer nickelates. Nat. Mater. 19, 381–385 (2020). https://doi.org/10.1038/s41563-019-0585-z

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• DOI: https://doi.org/10.1038/s41563-019-0585-z

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