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From perovskite to infinite-layer nickelates: Hole concentration from x-ray absorption

R. Pons1, M. Flavenot2, K. Fürsich1, E. Schierle3, E. Weschke3, M. R. Cantarino4, E. Goering1, P. Nagel5, S. Schuppler5 et al.

G. Kim1, G. Logvenov1, B. Keimer1,6, R. J. Green7,8, D. Preziosi2, and E. Benckiser1,6,*

  • *Contact author: E.Benckiser@fkf.mpg.de
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Phys. Rev. B 114, 175121 – Published 16 September, 2026

DOI: https://doi.org/10.1103/qc3z-k45l

Abstract

The difficulty of determining cation concentrations and oxygen stoichiometry in infinite-layer nickelate thin films has so far prevented clear experimental identification of the nickel electron configuration in the superconducting phase. We used soft x-ray absorption spectroscopy to study the successive changes in PrNiOx thin films at various intermediate stages of topotactic reduction with x=2–3. By comparing the NiL-edge spectra to single- and double-cluster ligand-field calculations, we find that none of our samples exhibits a pure d9 configuration. Our quantitative analysis using the charge sum rule shows that even when films are maximally reduced, the spatially averaged number of nickel 3d holes is 1.38. Superconducting samples have even higher values, calling into question the previously assumed limit of hole doping. Concomitant changes in the oxygen K-edge absorption spectra upon reduction indicate the presence of oxygen 2p holes, even in the most reduced films. Overall, our results suggest a complex interplay of hole-doping mechanisms resulting from self-doping effects, structural defects, and oxygen nonstoichiometry.

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Phys. Rev. B 114, 175121– Published 16 September, 2026
  • Received 20 November 2025
  • Revised 14 July 2026
  • Accepted 4 August 2026
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