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

Kagome materials are a class of materials with a lattice structure composed of corner-sharing triangles that give rise to 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, limiting the investigation of the emergent flat band physics. By combining soft X-ray angle-resolved resolved photoemission spectroscopy (ARPES) and the first-principles calculations, we reveal the electronic structure of a novel kagome metal CeNi5 with a clear dispersion along kz direction and a Fermi level flat band on the Γ-K-M-Γ plane. Besides, resonant ARPES experiments results indicate a near 4+ valence state of Ce ions, which is consistent with the transport measurements. 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 as well as the interaction between different types of flat bands by tuning the valence state of Ce ions.