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TT: Fachverband Tiefe Temperaturen

TT 39: Focus Session: Nickelate Superconductivity: Insights into Unconventional Pairing and Correlation Effects I (joint session TT/DS/MA)

TT 39.2: Topical Talk

Wednesday, March 11, 2026, 10:00–10:30, HSZ/0003

Recent insights into infinite-layer nickelate heterostructures from x-ray spectroscopy — •Eva Benckiser — Max Planck Institute for Solid State Research, Stuttgart, Germany

Nickelates have emerged as an important class of materials for studying unconventional superconductivity. However, the exact cation concentrations and oxygen stoichiometry in infinite-layer nickelates are difficult to determine due to the complex synthesis process. This has so far prevented the clear experimental identification of the nickel valence electron configuration in the superconducting phase.

In my talk, I will discuss our recent x-ray spectroscopy studies on NdNiO_x-SrTiO₃ heterostructures [1] and PrNiO_x thin films [2] at various intermediate stages of topotactic reduction with x=2−3. We find that even the most reduced films do not exhibit a pure Ni¹⁺-3d⁹ configuration. The quantitative analysis shows that there is an average of 1.35 holes in the nickel 3d states and superconducting samples have even higher values [2]. These results challenge previous findings regarding the doping range in which superconductivity occurs in infinite-layer nickelates. Variations between samples are attributed to a complex interplay of ordered, self-doped regions, interfacial reconstructions, and disorder occurring on different length scales in both the cation and anion sublattices.
[1] R. A. Ortiz et al., Phys. Rev. Materials 9, 054801 (2025).
[2] R. Pons et al., submitted (2025).

Keywords: Infinite-layer nickelates; Oxide heterostructures; High-temperature superconductivity; X-ray spectroscopy