  Layered kagome-lattice 3d transition metals are emerging as an exciting
platform to explore the frustrated lattice geometry and quantum topology.
However, the typical kagome electronic bands, characterized by sets of the
Dirac-like band capped by a phase-destructive flat band, have not been clearly
observed, and their orbital physics are even less well investigated. Here, we
present close-to-textbook kagome bands with orbital differentiation physics in
CoSn, which can be well described by a minimal tight-binding model with
single-orbital hopping in Co kagome lattice. The capping flat bands with
bandwidth less than 0.2 eV run through the whole Brillouin zone, especially the
bandwidth of the flat band of out-of-plane orbitals is less than 0.02 eV along
G-M. The energy gap induced by spin-orbit interaction at the Dirac cone of
out-of-plane orbitals is much smaller than that of in-plane orbitals,
suggesting orbital-selective character of the Dirac fermions.
