Inhomogeneity of the Ultrafast Insulator-to-Metal Transition Dynamics of VO₂

Abstract

The insulator-metal transition (IMT) of vanadium dioxide (VO₂) has remained a long-standing challenge in correlated electron physics. Here we reveal inhomogeneous behavior of individual VO₂ microcrystals using pump-probe microscopy and nanoimaging. The timescales of the ultrafast IMT vary from 40±8 fs to 200±20 fs with average values similar to results from polycrystalline thin-film studies. In combination with the observed sensitive variations in the thermal nanodomain IMT behavior, this suggests that the IMT is highly susceptible to local changes in doping, defects and strain. Our results suggest an electronic mechanism dominating the photoinduced IMT, but also highlight the difficulty to deduce microscopic mechanisms when the intrinsic material response is unclear.