Ultrafast insulator‐metal transition in VO2: interplay between coherent lattice motion and electronic correlations

The multi-THz conductivity of VO2 recorded during a photoinduced insulator-metal transition directly reveals the femtosecond dynamics of V-V stretching modes and electronic correlations. The strongly correlated character of the electronic system leads to a transient behaviour of the conductivity that cannot be understood in a Born-Oppenheimer picture. Based on our measurements with a time resolution of 12 fs and recent theoretical simulations for the electronic structure in steady state, we suggest a novel qualitative model for the non-thermal phase transition. The extremely high speed for the photoinduced phase transition is elegantly explained via a directed wave packet motion in the electronically excited state of the dimer that transfers the crystal structure of the insulator into the configuration of the metallic phase. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)