Nanotextured Dynamics of a Light-Induced Phase Transition in VO2

A. J. Sternbach, F. L. Ruta, Y. Shi, T. Slusar, J. Schalch, G. Duan, A. S. McLeod, X. Zhang, M. Liu, A. J. Millis, H. Kim, L. Chen, R. D. Averitt and D. N. Basov

Nanoletters 21,9052 (2021)
We investigate transient nanotextured heterogeneity in vanadium dioxide (VO2) thin films during a light-induced insulator-to-metal transition (IMT). Time-resolved scanning near-field optical microscopy (Tr-SNOM) is used to study VO2 across a wide parameter space of infrared frequencies, picosecond time scales, and elevated steady-state temperatures with nanoscale spatial resolution. Room temperature, steady-state, phonon enhanced nano-optical contrast reveals preexisting “hidden” disorder. The observed contrast is associated with inequivalent twin domain structures. Upon thermal or optical initiation of the IMT, coexisting metallic and insulating regions are observed. Correlations between the transient and steady-state nano-optical textures reveal that heterogeneous nucleation is partially anchored to twin domain interfaces and grain boundaries. Ultrafast nanoscopic dynamics enable quantification of the growth rate and bound the nucleation rate. Finally, we deterministically anchor photoinduced nucleation to predefined nanoscopic regions by locally enhancing the electric field of pump radiation using nanoantennas and monitor the on-demand emergent metallicity in space and time.