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  • Letter
  • Open Access

Orbital order and superconductivity in bilayer nickelate compounds

Giniyat Khaliullin1 and Jiří Chaloupka2

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Phys. Rev. B 113, L041115 – Published 20 January, 2026

DOI: https://doi.org/10.1103/4qsd-ws9c

Abstract

We propose a theory for bilayer nickelate materials, where a large tetragonal field—intrinsic or induced by epitaxial strain—lifts the orbital degeneracy and localizes the 3z2−r2 orbital states. These states host local spins S=1/2 bound into singlets by strong interlayer coupling, and their dynamics is described by weakly dispersive singlet-triplet excitations (“triplons”). The charge carriers occupy the wide bands of x2−y2 symmetry, and their Cooper pairing is mediated by the high-energy triplon excitations. As the x2−y2 band filling increases, i.e., moving further away from the Ni3+ valence state, the indirect Ruderman-Kittel-Kasuya-Yosida interactions between local spins induce spin-density-wave order via triplon condensation. Implications of the model for compressively strained La3Ni2O7 films and electron-doped oxychloride Sr3Ni2O5Cl2 are discussed.

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Phys. Rev. B 113, L041115– Published 20 January, 2026
  • Received 9 June 2025
  • Revised 4 December 2025
  • Accepted 2 January 2026
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Open access publication funded by Max Planck Society.

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