Softening of the insulating phase near Tc for the photo-induced insulator-to-metal phase transition in vanadium dioxide

摘要

We use optical-pump terahertz-probe spectroscopy to investigate thenear-threshold behavior of the photoinduced insulator-to-metal (IM) transitionin vanadium dioxide thin films. Upon approaching Tc a reduction in the fluencerequired to drive the IM transition is observed, consistent with a softening ofthe insulating state due to an increasing metallic volume fraction (below thepercolation limit). This phase coexistence facilitates the growth of ahomogeneous metallic conducting phase following superheating viaphotoexcitation. A simple dynamic model using Bruggeman effective medium theorydescribes the observed initial condition sensitivity.