Three-Dimensional van Hove Singularities and Charge Density Wave Evolution in Kagome Lattice KV₃Sb₅

The kagome metals AV_3Sb_5 (A = K, Rb, Cs) feature intertwined Dirac fermions, topological flat bands, and van Hove singularities (vHS) near the Fermi level, which give rise to a range of exotic, strongly correlated phenomena such as charge density waves (CDW) and superconductivity. Although the vHS from V 3d states have been implicated in CDW formation, their three-dimensional nature and temperature evolution remain poorly understood. In this study, we used high-resolution angle-resolved photoemission spectroscopy and density functional theory to reveal pronounced out-of-plane dispersion of vHS and their temperature dependence in KV_3Sb_5. The identified c-axis band folding and scattering channels were directly linked to the CDW order. These results demonstrate that the CDW transition in this family involves cooperative coupling between electron correlations and structural modulation along the c axis. This offers new insights into the interplay of topology, correlations, and lattice instabilities in kagome metals.