Kondo Effect in a 2D Kagome Metal-organic Framework on a Metal

The kagome lattice, hosting Dirac and flat electronic bands, offers a rich space to realise strongly correlated phases of matter in two-dimensional (2D) and layered materials. While strongly correlated electron phenomena have been observed in inorganic kagome systems, they remain unobserved in organic-based kagome ones. The latter offer versatile bottom-up synthesis protocols via self-assembly and metal-ligand coordination. Here, we report the synthesis of a 2D metal-organic framework (MOF) with honeycomb-kagome (HK) structure via coordination of Cu atoms with di-cyanoanthracene (DCA) molecules on an Ag(111) noble metal surface. Via low-temperature scanning tunneling spectroscopy (STS), we observe Kondo screening (by Ag(111) conduction electrons) of magnetic moments. From our temperature-dependent STS measurements, we determined a Kondo temperature of 124 (140) K associated with Cu (DCA, respectively). Our experiments are consistent with density functional theory and mean-field Hubbard modelling, which shows that the unpaired magnetic moments result directly from strong interactions between HK electrons. Our work paves the way for strongly correlated electronic phases of matter in - and strongly correlated electronics based on - atomically precise, self-assembled MOFs.