Experimental observation of Fermi-level flat band in novel kagome metal CeNi₅

Kagome materials are a class of material with a lattice structure composed of corner-sharing triangles that produce various exotic electronic phenomena, such as Dirac fermions, van Hove singularities, and flat bands. However, most of the known kagome materials have a flat band detached from the Fermi energy, which limits the investigation of the emergent flat band physics. In this work, by combining soft x-ray angle-resolved photoemission spectroscopy (ARPES) and the first-principles calculations, the electronic structure is investigated of a novel kagome metal CeNi₅ with a clear dispersion along the k_z direction and a Fermi level flat band in the Γ–K–M–Γ plane. Besides, resonant ARPES experimental results indicate that the valence state of Ce ions is close to 4⁺, which is consistent with the transport measurement result. Our results demonstrate the unique electronic properties of CeNi₅ as a new kagome metal and provide an ideal platform for exploring the flat band physics and the interactions between different types of flat bands by tuning the valence state of Ce ions.