Topological flat bands in a kagome lattice multiorbital system*

Flat bands and dispersive Dirac bands are known to coexist in the electronic bands in a two-dimensional kagome lattice. Including the relativistic spin-orbit coupling, such systems often exhibit nontrivial band topology, allowing for gapless edge modes between flat bands at several locations in the band structure, and dispersive bands or at the Dirac band crossing. Here, we theoretically investigate the electronic property of a multiorbital system on a kagome lattice. We found that the multiorbital kagome model with the atomic spin-orbit coupling naturally supports topological bands characterized by nonzero Chern numbers C, including a flat band with |C| =1. We further investigate the effect of Coulomb repulsive interactions. When such a flat band is 1/3 filled, the non-local repulsive interactions induce a fractional Chern insulating state. Thus, the multiorbital system on a kagome lattice is a versatile platform to explore the interplay between nontrivial band topology and electronic interaction. We also discuss the possible realization of our findings in real kagome materials.