Electronic structure of a 2D van der Waals Dirac metal with a flat band

Two-dimensional Dirac materials hosting flat bands have become a key area of interest in condensed matter physics, recognized for their diverse phenomena, such as high-temperature superconductivity and ferromagnetism. Flat bands typically arise due to strong electron correlations or frustrated lattice geometry. For the latter case, a well-known example is the kagome lattice, where Dirac and flat bands coexist. However, the realization of their coexistence in a real square lattice materials is rare. Using angle-resolved photoemission spectroscopy (ARPES), we identify the coexistence of Dirac and flat bands in the primitive square lattice compound Pd₅AlI₂. Our model calculations reveal that the decoration of a primitive square lattice with a specific set of atomic orbitals causes frustrated electron hopping, which leads to the formation of this flat band. Further, photon-energy dependence of electronic structure measurements shows the quasi-2D electronic nature of this material. Owing to the van der Waals nature, this material can be exfoliated to the monolayer limit, paving the way for exploring orbital physics in true 2D limit.