  Using the extensively studied V2O3 as a prototype system, we investigate the
role of percolation in metal-insulator transition (MIT). We apply scanning
microwave impedance microscopy to directly determine the metallic phase
fraction p and relate it to the macroscopic conductance G, which shows a sudden
jump when p reaches the percolation threshold. Interestingly, the conductance G
exhibits a hysteretic behavior against p, suggesting two different percolating
processes upon cooling and warming. Based on our image analysis and model
simulation, we ascribe such hysteretic behavior to different domain nucleation
and growth processes between cooling and warming, which is likely caused by the
decoupled structural and electronic transitions in V2O3 during MIT. Our work
provides a microscopic view of how the interplay of structural and electronic
degrees of freedom affects MIT in strongly correlated systems.
