Carrier-Induced\nMetal-to-Insulator Transition in Electrostatically\nDoped VO<sub>2</sub>

Metal-to-insulator transition (MIT) in strongly correlated\nelectronic\nsystems such as vanadium dioxide (VO<sub>2</sub>) is known to be modulated\nby carrier doping. However, previous attempts show modification of\ncarriers in VO<sub>2</sub> are always concomitant with lattice distortions,\nmaking it challenging to decouple pure electronic contribution in\nMIT. In this work, we synthesize and demonstrate a pure filling-controlled\nMIT in VO<sub>2</sub> using modulation-doped heterostructures. With\na combination of electrical transport and hall measurements, we show\nthat carrier concentrations in VO<sub>2</sub> can be modulated both\nby varying the dopant densities in the dopant layer and by varying\nthe thickness of the VO<sub>2</sub> layer. The increase in carrier\ndensities up to ∼10<sup>21</sup> cm<sup>–3</sup> in\nthe insulating phase led to a decrease in transition temperatures\nby ∼40 K. Additionally, X-ray photoelectron spectroscopy was\nutilized to rule out the presence of oxygen vacancies as a source\nof electron donors in VO<sub>2</sub>. We further present that the\nmodulation-doped heterostructures with an amorphous insulating spacer\nlayer offer unambiguous evidence of pure filling-controlled MIT in\nVO<sub>2</sub>. Our work shows that modulation doping is a potent\nstrategy for realizing carrier-induced condensed matter phases in\nother correlated electronic systems, paving the pathway for the possible\ndevelopment of Mott devices.