Chern insulator with a nearly flat band in the metal-organic-framework-based Kagome lattice.

Based on first-principles density-functional theory (DFT) calculations, we report that the transition-metal bis-dithiolene, M3C12S12 (M = Mn and Fe), complexes can be a two-dimensional (2D) ferromagnetic insulator with nontrivial Chern number. Among various synthetic pathways leading to metal bis-dithiolenes, the simplest choice of ligand, Benzene-hexathiol, connecting metal cations to form a Kagome lattice is studied following the experimental report of time-reversal symmetric isostructural compound Ni3C12S12. We show sulfur and carbon-based ligands play the key role in making the complexes topologically nontrivial. An unusual topological quantum phase transition induced by the on-site Coulomb interaction brings a nearly flat band with a nonzero Chern number as the highest occupied band. With this analysis we explain the electronic structure of the class M3C12S12 and predict the existence of nearly flat band with nonzero Chern number and it can be a fractional Chern insulator candidate with carrier doping.