Cuprate-like Electronic Structures in Infinite-Layer Nickelates with 3D dispersion

The discovery of superconductivity in the infinite-layer (IL) nickelates provides a new platform and angle of view to study the long-standing problem of high temperature superconductivity . Many models were proposed to understand its superconducting mechanisms based on the calculated electronic structure, and the multiple Fermi surfaces and multiple orbitals involved create complications and controversial conclusions. Over the past 5 years, the lack of direct measurements of the electronic structure has hindered the understanding of nickelate superconductors. Here, we fill this gap by preparing IL LaNiO_2 and La_0.8Ca_0.2NiO_2 thin films with superior surface quality and measuring their electronic structure by angle-resolved photoemission spectroscopy (ARPES).The Fermi surface consists of a large three-dimensional hole pocket primarily contributed by Ni-3d_x^2-y^2 states, and a small electron pocket at the Brillouin zone (BZ) corner. The hole pocket exhibits a two-dimensional character over approximately 80 Fermi surface topology and band dispersion closely resemble those observed in hole-doped cuprates, suggesting their superconducting mechanisms may be alike. Yet this hole pocket shows strong three-dimensional character near k_z=π, which deviates from previous calculations and adds new facets to the superconductivity in IL nickelates. The experimental electronic structure represents a pivotal step toward a microscopic understanding of the IL nickelate family and its superconductivity.