  Electron-electron interactions in materials lead to exotic many-body quantum
phenomena including Mott metal-insulator transitions (MITs), magnetism, quantum
spin liquids, and superconductivity. These phases depend on electronic band
occupation and can be controlled via the chemical potential. Flat bands in
two-dimensional (2D) and layered materials with a kagome lattice enhance
electronic correlations. Although theoretically predicted, correlated-electron
Mott insulating phases in monolayer 2D metal-organic frameworks (MOFs) with a
kagome structure have not yet been realised experimentally. Here, we synthesise
a 2D kagome MOF on a 2D insulator. Scanning tunnelling microscopy (STM) and
spectroscopy reveal a MOF electronic energy gap of ~200 meV, consistent with
dynamical mean field theory predictions of a Mott insulator. Combining
template-induced (via work function variations of the substrate) and STM
probe-induced gating, we locally tune the electron population of the MOF kagome
bands and induce Mott MITs. These findings enable technologies based on
electrostatic control of many-body quantum phases in 2D MOFs.
