Interplay between fermiology and electron correlation is crucial for realizing exotic quantum phases. Transition-metal dichalcogenide (TMD) $1T\text{−}{\mathrm{TaS}}_2$ has sparked tremendous attention owing to its unique Mott-insulating phase coexisting with the charge-density wave (CDW). However, how the fermiology and electron correlation are associated with such properties has yet to be clarified. Here we demonstrate that monolayer $1T\text{−}{\mathrm{NbTe}}_2$ is a new class of two-dimensional TMD which has the star-of-David lattice similarly to bulk ${\mathrm{TaS}}_2$ and isostructural monolayer ${\mathrm{NbSe}}_2$, but exhibits a metallic ground state with an unusual lattice periodicity ($\sqrt{19}\times \sqrt{19}$) characterized by the sparsely occupied star-of-David lattice. By using angle-resolved photoemission and scanning-tunneling spectroscopies in combination with first-principles band-structure calculations, we found that the hidden Fermi-surface nesting and associated CDW formation are a primary cause to realize this unique correlated metallic state with no signature of Mott gap. The present result points to a vital role of underlying fermiology to characterize the Mott phase of TMDs.

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• Electronic structure
• Transition metal dichalcogenides
• Angle-resolved photoemission spectroscopy
• Scanning tunneling microscopy