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 ultra-high vacuum 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 waterfall-like 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.
@article{arxiv.2604.08430,
title = {Three-Dimensional Electronic Structures in Superconducting Ruddlesden-Popper Bilayer Nickelate Films},
author = {Yueying Li and Lizhi Xu and Wei Lv and Zihao Nie and Zechao Wang and Yu Miao and Jianchang Shen and Guangdi Zhou and Wenhua Song and Heng Wang and Haoliang Huang and Junfeng He and Jin-Feng Jia and Peng Li and Qi-Kun Xue and Zhuoyu Chen},
journal= {arXiv preprint arXiv:2604.08430},
year = {2026}
}