We explore the optical properties of La₃Ni₂O₇ bilayer nickelates by using density functional theory including a Coulomb repulsion term. Convincing agreement with recent experimental ambient-pressure spectra is achieved for U ~ 3 eV, which permits tracing the microscopic origin of the characteristic features. Simultaneous consistency with angle-resolved photoemission spectroscopy and x-ray diffraction suggests the notion of rather moderate electronic correlations in this novel high-T_c superconductor. Oxygen vacancies form predominantly at the inner apical sites and renormalize the optical spectrum quantitatively, while the released electrons are largely accommodated by a defect state. We show that the structural transition occurring under high pressure coincides with a significant enhancement of the Drude weight and a reduction of the out-of-plane interband contribution that acts as a fingerprint of the emerging hole pocket. We further calculate the optical spectra for various possible magnetic phases including spin-density waves and discuss the results in the context of experiment. Finally, we investigate the role of the 2–2 versus 1–3 layer stacking and compare the bilayer nickelate to La₄Ni₃O₁₀, La₃Ni₂O₆, and NdNiO₂, unveiling general trends in the optical spectrum as a function of the formal Ni valence in Ruddlesden–Popper versus reduced Ruddlesden–Popper nickelates.

我们使用包括库仑排斥项在内的密度泛函理论来探索 La₃Ni₂O₇ 双层镍酸盐的光学性质。与 U ~ 3 eV 的最近实验环境压力谱达成了令人信服的一致性，这允许追踪特征特征的微观起源。与角度分辨光电子发射光谱和 X 射线衍射同时保持一致，这表明在这种新型高 T_c 超导体中存在相当适度的电子相关性。氧空位主要在根尖内位形成，并定量地重新标准化光谱，而释放的电子主要由缺陷状态容纳。我们表明，在高压下发生的结构转变与 Drude 权重的显着增加和作为新兴空穴指纹的平面外带间贡献的减少相吻合。我们进一步计算了各种可能的磁相（包括自旋密度波）的光谱，并在实验背景下讨论了结果。最后，我们研究了 2-2 层与 1-3 层堆叠的作用，并将双层镍酸盐与 La₄Ni₃O₁₀、La₃Ni₂O₆ 和 NdNiO₂ 进行了比较，揭示了光谱中作为 Ruddlesden-Popper 中形式 Ni 价与还原 Ruddlesden-Popper 镍酸盐的函数的一般趋势。