Magic Defect Site for Modulating Electron-Correlated Properties in Monolayer T-NbSe.

Defect engineering provides a precise and controlled approach to modify the localized electronic properties through crystalline interruption. In 2D electron-correlated materials, periodic lattice distortions often coexist with charge density waves (CDWs) and Mott insulating states, which are highly sensitive to local electronic environments. However, the influence of complex, inequivalent defect sites on electron-correlated properties, particularly Mott behavior, remains poorly understood. Here, density functional theory calculation is utilized to investigate the electron-correlated properties of monolayer T-NbSe with various single selenium/niobium vacancies. It is found that a single vacancy can induce geometric alterations over several nanometers, distinguished from typical 2D materials. A unique selenium vacancy site can precisely eliminate Mott electrons of T-NbSe and gradually lead the transitions from a ferromagnetic charge transfer insulator into a non-magnetic band insulator. Moreover, writing in and erasing Mott electrons can be flexibly manipulated by substituting the selenium site with arsenic, bromine, and potassium elements. The modulation mechanism by selenium vacancy originates from a synergistic combination of compressive strain and electron doping. The results systematically reveal that defect engineering is an ingenious strategy for atomically manipulating electron-correlated properties and manufacturing electronic patterns, enabling the control of Mott electrons in 2D materials.