Rich nature of Van Hove singularities in Kagome superconductor CsV3Sb5

Predictions suggest enhanced correlation effect due to multiple van Hove singularities (VHS) in the vicinity of the Fermi level in the recently discovered AV(3)Sb(5) kagome metals. Here the authors identify three VHSs close to the Fermi level with diverse sublattice characters in CsV3Sb5, and one of them shows flat dispersion suggesting the higher-order nature. The recently discovered layered kagome metals AV(3)Sb(5) (A = K, Rb, Cs) exhibit diverse correlated phenomena, which are intertwined with a topological electronic structure with multiple van Hove singularities (VHSs) in the vicinity of the Fermi level. As the VHSs with their large density of states enhance correlation effects, it is of crucial importance to determine their nature and properties. Here, we combine polarization-dependent angle-resolved photoemission spectroscopy with density functional theory to directly reveal the sublattice properties of 3d-orbital VHSs in CsV3Sb5. Four VHSs are identified around the M point and three of them are close to the Fermi level, with two having sublattice-pure and one sublattice-mixed nature. Remarkably, the VHS just below the Fermi level displays an extremely flat dispersion along MK, establishing the experimental discovery of higher-order VHS. The characteristic intensity modulation of Dirac cones around K further demonstrates the sublattice interference embedded in the kagome Fermiology. The crucial insights into the electronic structure, revealed by our work, provide a solid starting point for the understanding of the intriguing correlation phenomena in the kagome metals AV(3)Sb(5).