近日，清华大学的王亚愚及其研究小组与中国科学院物理研究所的陈震以及中山大学的王猛等人合作并取得一项新进展。经过不懈努力，他们实现La₃Ni₂O_7-δ中氧空穴和自掺杂配体空穴的可视化。相关研究成果已于2024年6月5日在国际权威学术期刊《自然》上发表。

该研究团队研发了一种新颖的能量过滤多层电子叠层成像技术，并结合电子能量损失谱，以攻克关键科研难题。该技术使氧空穴得以直接可视化，并发现它们主要占据内部顶端位点，这被认为是超导性能的关键所在。研究人员精确测定了纳米级化学计量学及其与氧K边缘光谱的关联性，揭示了样品中氧含量和电子结构的显著不均匀性。

光谱分析进一步表明，化学计量La₃Ni₂O_7-δ具有显著的电荷转移特性，空穴从Ni位点自掺杂到O位点。空穴在内顶端O和平面O上分布较为集中，而在外顶端O上的密度几乎可以忽略不计。随着O空穴浓度的增加，这两个位点上的空穴同时减少。这些观察结果将有助于进一步发展和理解超导镍酸盐材料。这项成像技术定量化原子缺陷也可以广泛应用于材料科学和凝聚态物理。

据悉，最近发现的La₃Ni₂O_7-δ在高压下具有超导性，其转变温度高达约80K，这一发现激发了广泛的实验和理论研究。然而，关于其配对机制的几个核心问题尚未有确切答案，例如最相关的原子轨道和原子缺陷的作用。

附：英文原文

Title: Visualization of oxygen vacancies and self-doped ligand holes in La₃Ni₂O_7-δ

Author: Dong, Zehao, Huo, Mengwu, Li, Jie, Li, Jingyuan, Li, Pengcheng, Sun, Hualei, Gu, Lin, Lu, Yi, Wang, Meng, Wang, Yayu, Chen, Zhen

Issue&Volume: 2024-06-05

Abstract: The recent discovery of superconductivity in La₃Ni₂O_7-δ under high pressure with a transition temperature around 80K (ref. 1) has sparked extensive experimental and theoretical efforts. Several key questions regarding the pairing mechanism remain to be answered, such as the most relevant atomic orbitals and the role of atomic deficiencies. Here we develop a new, energy-filtered, multislice electron ptychography technique, assisted by electron energy-loss spectroscopy, to address these critical issues. Oxygen vacancies are directly visualized and are found to primarily occupy the inner apical sites, which have been proposed to be crucial to superconductivity. We precisely determine the nanoscale stoichiometry and its correlation to the oxygen K-edge spectra, which reveals a significant inhomogeneity in the oxygen content and electronic structure within the sample. The spectroscopic results also reveal that stoichiometric La₃Ni₂O₇ has strong charge-transfer characteristics, with holes that are self-doped from Ni sites into O sites. The ligand holes mainly reside on the inner apical O and the planar O, whereas the density on the outer apical O is negligible. As the concentration of O vacancies increases, ligand holes on both sites are simultaneously annihilated. These observations will assist in further development and understanding of superconducting nickelate materials. Our imaging technique for quantifying atomic deficiencies can also be widely applied in materials science and condensed-matter physics.

DOI: 10.1038/s41586-024-07482-1

Source: https://www.nature.com/articles/s41586-024-07482-1