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Three-Dimensional Electronic Structures in Superconducting Ruddlesden-Popper Bilayer Nickelate Films

Yueying Li1,2,*, Lizhi Xu1,*, Wei Lv1,*, Zihao Nie1, Zechao Wang1, Yu Miao3, Jianchang Shen3, Guangdi Zhou1,2, Wenhua Song1 et al.

Heng Wang1,2, Haoliang Huang1,2, Junfeng He3, Jin-Feng Jia1,2,4, Peng Li1,2,†, Qi-Kun Xue1,2,5,‡, and Zhuoyu Chen1,2,§

  • *These authors contributed equally to this work.
  • †Contact author: lipeng@quantumsc.cn
  • ‡Contact author: xueqk@sustech.edu.cn
  • §Contact author: chenzhuoyu@sustech.edu.cn
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Phys. Rev. X 16, 031016 – Published 24 July, 2026

DOI: https://doi.org/10.1103/466c-8sl4

Abstract

Beyond the quasi-two-dimensional (2D) paradigm of cuprates, the role of the third dimension of the Ruddlesden-Popper bilayer nickelates is essential to decoding their superconducting mechanism. Here, using angle-resolved photoemission spectroscopy (ARPES) with varied photon energies, we systematically investigate the electronic band structures in three dimensions for superconducting (La,Pr,Sm)3Ni2O7/SrLaAlO4 thin films (superconducting onset temperature Tconset∼48  K) transferred via a cryogenic ultrahigh vacuum (UHV) suitcase. We reveal an orbital-dependent dimensionality: While the dx2−y2-dominant bands exhibit a quasi-2D character, the dz2-dominant band displays a finite kz dispersion. Finite energy gaps are identified on all observed bands across multiple high-symmetry directions. Systematic temperature-dependent analysis characterizes the superconducting nature of the gap on the dz2-derived band, revealing a large gap Δ∼18  meV and a ratio 2Δ/kBTc∼8 exceeding the weak-coupling BCS limit. The suppression of spectral weight near the Fermi level persists above the superconducting transition temperature. Ubiquitous vertical spectral features evidence the presence of electron interactions. These results underscore the role of the dz2 orbital and correlations, placing constraints on theoretical models for nickelate superconductivity.

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Popular Summary

Determining the microscopic mechanism that drives high-temperature superconductivity in Ruddlesden-Popper nickelates is a persistent challenge due to ongoing debates regarding the dimensionality of their electronic states and the precise roles of specific atomic orbitals. We addressed this controversy by using angle-resolved photoemission spectroscopy combined with a cryogenic vacuum sample transfer technique to map the complete three-dimensional electronic structure of superconducting bilayer nickelate thin films. Our measurements explicitly reveal a prominent out-of-plane dispersion for the dz2-derived electronic band, establishing its intrinsic three-dimensional character. We further identified finite, nodeless superconducting gaps across all observed bands, with a large gap ratio that signals a strong-coupling pairing regime possibly driven by electron correlations. Our work establishes an experimental foundation that guides future theoretical and experimental exploration of unconventional superconductivity.

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Phys. Rev. X 16, 031016– Published 24 July, 2026
  • Received 23 December 2025
  • Revised 9 April 2026
  • Accepted 19 May 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.

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