Constant threshold resistivity in the metal-insulator transition of VO ₂

We report a constant threshold resistivity observed for the insulating phase of VO₂ before it transfers into the metallic phase, regardless of the initial resistivity, transition temperature, and strain state. The value of the threshold resistivity is also comparable for different lattice structures of the insulating phase. Such a constant threshold resistivity suggests that a constant critical free-electron concentration is needed on the insulating side to trigger the insulator-to-metal transition, indicating the electronic nature of the mechanism of the transition.