Non-thermal nature of photo-induced insulator-to-metal transition in NbO${}_2$

Abstract

We study the photo-induced metallization process in niobium dioxide NbO${}_2$. This compound undergoes the thermal insulator-to-metal transition at the remarkably high temperature of 1080 K. Our optical pump - terahertz probe measurements reveal the ultrafast switching of the film on a sub-picosecond timescale and the formation of a metastable metallic phase when the incident pump fluence exceeds the threshold of 10 mJ/cm${}^2$. Remarkably, this threshold value corresponds to the deposited energy which is capable of heating NbO${}_2$ only up to 790 K, thus, evidencing the non-thermal character of the photo-induced insulator-to-metal transition. We also observe an enhanced formation of the metallic phase above the second threshold of 17.5 mJ/cm${}^2$ which corresponds to the onset of the thermal switching. The transient optical conductivity in the metastable phase can be modeled using the Drude-Smith model confirming its metallic character. The present observation of non-thermal transition in NbO${}_2$ can serve as an important test bed for understanding photo-induced phenomena in strongly correlated oxides.

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Cited by in corpus (4)

• The critical role of hot carrier cooling in optically excited structural transitions
• Reconciling the theoretical and experimental electronic structure of NbO2
• Correlation induced emergent charge order in metallic vanadium dioxide
• Ultrafast dynamics of atomic correlated disordering in photoinduced VO${}_2$