  The doped Hubbard model is one of the paradigmatic platforms to engineer
exotic quantum many-body states, including charge-ordered states, strange
metals and unconventional superconductors. While undoped and doped correlated
phases have been experimentally realized in a variety twisted van der Waals
materials, experiments in monolayer materials, and in particular 1T transition
metal dichalcogenides, have solely reached the conventional insulating undoped
regime. Correlated phases in monolayer two-dimensional materials have much
higher associated energy scales than their twisted counterparts, making doped
correlated monolayers an attractive platform for high temperature correlated
quantum matter. Here, we demonstrate the realization of a doped Mott phase in a
van der Waals dichalcogenide 1T-NbSe$_2$ monolayer. The system is electron
doped due to electron transfer to a monolayer van der Waals substrate via
proximity, leading to a correlated triangular lattice with both half-filled and
fully-filled sites. We analyze the distribution of the half-filled and filled
sites and show the arrangement is unlikely to be controlled by disorder alone,
and we show that the presence of competing non-local many-body correlations
would account for the charge correlations found experimentally. Our results
establish 1T-NbSe$_2$ as a potential monolayer platform to explore correlated
doped Mott physics in a frustrated lattice.
