Ultrafast photoinduced insulator-to-metal transitions in vanadium dioxide

An explanation is given for the ultrafast insulator-to-metal transition in VO2 following photoexcitation. The photoinduced orbital imbalance induces a coherent motion of the V-V dimers affecting the electronic structure. After the closing of the gap, Boltzmann scattering equilibrates the electron densities. If the electron density exceeds a critical value, a phase transition occurs to the metallic state. The model explains several key features, such as a structural bottleneck, coherent structural motion combined with phase shifts in the oscillation, the absence of ultrafast metal-to-insulator transitions, and the need for a critical fluency.