近日，中国科学技术大学何俊峰团队研究了超导（La,Pr）₃Ni₂O₇/SrLaAlO₄异质结构的角分辨光谱学。2025年5月21日出版的《国家科学评论》杂志发表了这项成果。

在环境压力下发现的Ruddlesden-Popper双层镍酸盐薄膜超导体为研究超导态的电子结构提供了巨大的可能性。研究组报告了通过纯氧原位样品传输对生长在SrLaAlO₄亚态上的1、2和3晶胞外延La_2.85Pr_0.15Ni₂O₇薄膜的角分辨光电子能谱（ARPES）测量。使用具有不同探测深度的光子获得的证据表明，传导主要局限于界面附近的第一个晶胞。扫描透射电子显微镜（STEM）、能量色散X射线光谱（EDS）和电子能量损失光谱（EELS）表明，界面Sr扩散和明显的p-d杂化梯度可能共同解释了界面传导的限制。 

费米表面图揭示了与非超导环境压力块体晶体相比的空穴掺杂。色散带结构的测量表明，费米能级上的Ni d_x2-y2和d_z2轨道都有贡献。密度泛函理论（DFT）+U计算捕捉到了ARPES结果的定性特征，与空穴掺杂情况一致。这些发现约束了超导机制的理论模型，并表明在环境压力下提高镍酸盐超导性的潜力。

附：英文原文

Title: Angle-resolved photoemission spectroscopy of superconducting (La,Pr)3Ni2O7/SrLaAlO4 heterostructures

Author: Li, Peng, Zhou, Guangdi, Lv, Wei, Li, Yueying, Yue, Changming, Huang, Haoliang, Xu, Lizhi, Shen, Jianchang, Miao, Yu, Song, Wenhua, Nie, Zihao, Chen, Yaqi, Wang, Heng, Chen, Weiqiang, Huang, Yaobo, Chen, Zhen-Hua, Qian, Tian, Lin, Junhao, He, Junfeng, Sun, Yu-Jie, Chen, Zhuoyu, Xue, Qi-Kun

Issue&Volume: 2025-05-21

Abstract: Ruddlesden-Popper bilayer nickelate thin film superconductors discovered under ambient pressure enable vast possibilities for investigating electronic structures of the superconducting state. Here, we report angle-resolved photoemission spectroscopy (ARPES) measurements of 1, 2, and 3 unit-cell epitaxial La2.85Pr0.15Ni2O7 films grown on SrLaAlO4 substates, through pure-oxygen in situ sample transportation. Evidence obtained using photons with distinct probing depths shows that conduction is localized primarily at the first unit cell near the interface. Scanning transmission electron microscopy (STEM), together with energy-dispersive X-ray spectroscopy (EDS) and electron energy loss spectroscopy (EELS), indicates that interfacial Sr diffusion and pronounced p-d hybridization gradient may collectively account for the interfacial confinement of conduction. Fermi surface maps reveal hole doping compared to non-superconducting ambient-pressure bulk crystals. Measurements of dispersive band structures suggest the contributions from both Ni dx2-y2 and dz2 orbitals at the Fermi level. Density functional theory (DFT) + U calculations capture qualitative features of the ARPES results, consistent with a hole-doped scenario. These findings constrain theoretical models of the superconducting mechanism and suggest potential for enhancing superconductivity in nickelates under ambient pressure.

DOI: 10.1093/nsr/nwaf205

Source: https://academic.oup.com/nsr/advance-article/doi/10.1093/nsr/nwaf205/8140053