Two-dimensional (2D) and layered electronic materials characterized by a kagome lattice, whose valence band structure includes two Dirac bands and one flat band, can host a wide range of tunable topological and strongly correlated electronic phases. Here, direct experimental evidence of solid electron–electron Coulomb interactions in a 2D metal–organic framework (MOF) is reported. The MOF consists of 9,10-dicyanoanthracene (DCA) molecules arranged in a kagome structure via coordination with copper (Cu) atoms. On a silver surface, Ag(111), temperature-dependent scanning tunnelling spectroscopy (STS) reveals the presence of local magnetic moments at DCA and Cu sites of the MOF which is Kondo screened by the Ag(111) conduction electrons. This is a signature created by strong electron-electron correlations within the MOF.
Further evidence for strongly correlated electrons is detected in the same MOF on a thin insulating substrate, hexagonal boron nitride. Here, we are able to directly observe a ~200 meV bandgap in the MOF density of states via STS. These are promising findings for controlling correlated electronic phases in 2D organic materials with the potential for nanoelectronics and spintronics technologies.