Electronic structure of superconducting infinite-layer lanthanum nickelates

Revealing the momentum-resolved electronic structure of infinite-layer nickelates is essential for understanding this class of unconventional superconductors but has been hindered by the formidable challenges in improving the sample quality. In this work, we report the angle-resolved photoemission spectroscopy of superconducting La_0.8Sr_0.2NiO₂ films prepared by molecular beam epitaxy and in situ atomic-hydrogen reduction. The measured Fermi topology closely matches theoretical calculations, showing a large Ni $d_{x^2-y^2}$–derived Fermi sheet that evolves from hole-like to electron-like along k_z and a three-dimensional (3D) electron pocket centered at the Brillouin zone corner. The Ni $d_{x^2-y^2}$–derived bands show a mass enhancement (m*/m_DFT) of 2 to 3, while the 3D electron band shows negligible band renormalization. Moreover, the Ni $d_{x^2-y^2}$–derived states also display a band dispersion anomaly at higher binding energy, reminiscent of the waterfall feature and kinks observed in cuprates.