The discovery of superconductivity in infinite-layer (IL) nickelates has opened a new frontier for investigating the mechanisms of high-temperature superconductivity. Although their Ni d_x2−y2 band resembles that of cuprates, the presence of additional Fermi surface pockets and multi-orbital contributions has led to competing theories and unsettled debates. A central challenge has been the lack of direct experimental knowledge of their low-energy electronic structure. We performed angle-resolved photoemission spectroscopy (ARPES) studies on IL nickelates with improved surface quality and resolved the key electronic features of optimally doped IL nickelates and their parent compounds LaNiO₂ and NdNiO₂. Our measurements show that the additional electron-like pocket arises primarily from interstitial sstates with electride-like character, rather than rare-earth 5d or 4f orbitals, and that the rare-earth element tunes Ni-derived bands through a chemical pressure effect. These findings establish the orbital origin of the extra Fermi surfaces, clarify the role of rare-earth ions in shaping the band structure, and demonstrate the existence of electride-like interstitial carriers in a correlated oxide system. In hole-doped La_0.8Ca_0.2NiO₂, we further observe momentum-dependent spectral weight suppression and marginal-Fermi liquid behavior. Moreover, we found intrinsic bulk superconductivity in undoped PrNiO₂with distinctive properties that suggest a novel superconducting regime. Together, our findings highlight the unique physics of IL nickelates and provide fresh insight into the strange normal state and superconductivity in this new superconductor family. [1,2]

Our recent resonant inelastic x-ray scattering (RIXS) and STM studies of the spin excitations and density waves in trilayer perovskite nickelate La₄Ni₃O₁₀ will be briefly discussed as well. Compared with its bilayer sibling, La₄Ni₃O₁₀seems to have weaker electronic correlations and a substantially reduced interlayer magnetic exchange interaction. [3,4]

[1] X. Ding, et al., National Science Review, 11, nwae194 (2024).

[2] C. Li, et al.,Physical Review Letters 135: 116501(2025).

[3] M. Z. Li, et al. Phys. Rev. B 112, 045132 (2025).

[4] X. Y. Chen, et al. https://arxiv.org/pdf/2604.01902