Three-Dimensional van Hove Singularities and Charge Density Wave Evolution in kagome lattice KV₃Sb₅

The kagome metals AV₃Sb₅ (A = K, Rb, Cs) exhibit intertwined Dirac fermions, topological flat bands, and van Hove singularities (vHS) near the Fermi level, triggering the emergence of exotic strongly correlated phenomena such as charge density waves (CDW) and superconductivity. While the vHS from V 3d states have been implicated in CDW formation, their three-dimensional nature and temperature evolution remain poorly understood. Using high-resolution angle-resolved photoemission spectroscopy and density functional theory, we reveal pronounced out-of-plane dispersion of the vHS and their temperature dependence in KV₃Sb₅, and identify the c-axis band folding and scattering channels directly linked to the CDW order. These results demonstrate that the CDW transition in this family involves a cooperative coupling between electron correlations and structural modulation along the c axis, offering new insight into the interplay of topology, correlations, and lattice instabilities in kagome metals.