Persistent Mottness in electron-doped 1T-TaS₂

Persistence of the Mott insulating state away from integer filling remains unresolved. Although it is often attributed to electronic phase separation, theoretical models still predict a critical doping that differs markedly from experiments. Here, we show that intrinsic disorder is the missing ingredient. Scanning tunnelling microscopy and spectroscopy measurements on Fe-intercalated 1T-TaS₂, an electron-doped Mott insulator, reveal Mott regions nucleated at point defects and charge density wave domain boundaries. These defects act as local charge sinks; the resulting sharp chemical potential differences produce narrow Mott depletion plateaus. In contrast, the hole-doped 1T-TaS₂ layer of 4Hb-TaS₂ displays no incompressible regions in the vicinity of similar impurities. This contrasting behaviour demonstrates that local disorder which compensates for the doping effect plays a key role in shaping the inhomogeneous electronic structure of doped Mott insulators.