  Kagome materials exhibit many novel phenomena emerging from the interplay
between lattice geometry, electronic structure, and topology. A prime example
is the vanadium-based kagome materials AV3Sb5 (A = K, Rb, and Cs) with
superconductivity and unconventional charge-density wave (CDW). More
interestingly, the substitution of vanadium by chromium further introduces
magnetism and enhances the correlation effect in CsCr3Sb5 which likewise
exhibits superconductivity under pressure and competing density-wave state.
Here we systematically investigate the electronic structure of CsCr3Sb5 using
high-resolution angle-resolved photoemission spectroscopy (APRES) and ab-initio
calculations. Overall, the measured electronic structure agrees with the
theoretical calculation. Remarkably, Cr 3d orbitals exhibit incoherent
electronic states and contribute to incipient flat bands close to the Fermi
level. The electronic structure shows a minor change across the magnetic
transition at 55 K, suggesting a weak interplay between the local magnetic
moment and itinerant electrons. Furthermore, we reveal a drastic enhancement of
the electron scattering rate across the magnetic transition, which is relevant
to the semiconducting-like transport property of the system at high
temperatures. Our results suggest that CsCr3Sb5 is a strongly correlated Hund's
metal with incipient flat bands near the Fermi level, which provides an
electronic basis for understanding its novel properties in comparison to the
non-magnetic and weakly correlated AV3Sb5.
