We report direct spectroscopic evidence of correlation-driven Mott states in layered ${\mathrm{Nb}}_3{\text{Cl}}_8$ through combining scanning tunneling microscopy (STM) and dynamical mean-field theory. The Hubbard bands persist down to monolayer, providing the definitive evidence for the Mottness in ${\mathrm{Nb}}_3{\text{Cl}}_8$. While the size of the Mott gap remains almost constant across all layers, a striking layer-parity-dependent oscillation emerges in the local density of states (LDOS) between even ($n=2$, 4, 6) and odd layers ($n=1$, 3, 5), which arises from the dimerization and correlation modulation of the obstructed atomic states, respectively. Our conclusions are supported by a critical technical advance in atomic-scale LDOS mapping for highly insulating systems. This Letter provides the definitive experimental verification of correlation-driven Mott ground states in ${\mathrm{Nb}}_3{\text{Cl}}_8$, while establishing a general protocol for investigating the interplay of electronic correlation and interlayer coupling in layered insulators by using a low-temperature STM technique.

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• Electronic structure
• Mott insulators
• Dynamical mean field theory
• Scanning tunneling spectroscopy