transition metal-based kagome lattices*

Electronic flat bands in momentum space, arising from strong localization of electrons in real space, are an ideal stage to realize strong correlation phenomena as highlighted by the recent example of twisted-bilayer graphene. In certain lattice systems, electronic flat bands with nontrivial topology may naturally arise from the combination of geometrical frustration, spin-orbit coupling, and reduced dimensionality, while their experimental realization has been elusive so far. Here, we report the observation of topological flat bands in series of 3d transition metal-based kagome compounds. Using angle-resolved photoemission spectroscopy, we directly show how the dispersion of the flat bands is strongly quenched along all three momentum directions. Spin-orbit coupling opens a large gap at the quadratic band touching point between the Dirac and flat bands, endowing a nonzero Z₂ topological invariant to the flat band. Our observation opens a promising route to engineer novel emergent phases at the crossroad between strong correlated and topological materials.