  The layered vanadium antimonides AV3Sb5 (A = K, Rb, Cs) are a recently
discovered family of topological kagome metals with a rich phenomenology of
strongly correlated electronic phases including charge order and
superconductivity. Understanding how the singularities inherent to the kagome
electronic structure are linked to the observed many-body phases is a topic of
great interest and relevance. Here, we combine angle-resolved photoemission
spectroscopy and density functional theory to reveal multiple kagome-derived
van Hove singularities (vHs) coexisting near the Fermi level of CsV3Sb5 and
analyze their contribution to electronic symmetry breaking. Intriguingly, the
vHs in CsV3Sb5 have two distinct flavors - p-type and m-type - which originate
from their pure and mixed sublattice characters, respectively. This twofold vHs
is unique property of the kagome lattice, and its flavor critically determines
the pairing symmetry and ground states emerging in AV3Sb5 series. We establish
that, among the multiple vHs in CsV3Sb5, the m-type vHs of the dxz/dyz kagome
band and the p-type vHs of the dxy/dx2-y2 kagome band cross the Fermi level to
set the stage for electronic symmetry breaking. The former band exhibits
pronounced Fermi surface nesting, while the latter contributes via higher-order
vHs. Our work reveals the essential role of kagome-derived vHs for the
collective phenomena realized in the AV3Sb5 family, paving the way to a deeper
understanding of strongly correlated topological kagome systems.
