Decoupling between metal-insulator transition and structural phase transition in an interface-engineered VO.

The coupling between the metal-insulator transition (MIT) and the structural phase transition (SPT) in VO has been at the center of discussion for several decades, while the underlying mechanisms of electron-lattice or electron-electron interactions remain an open question. Until recently, the equilibrium state VO is believed to be a non-standard Mott-Hubbard system, i.e., both of the two interactions cooperatively work on MIT, indicating the association between MIT and SPT. However, due to the pronounced contribution of strain in strongly correlated systems, it is desirable to explore the correspondence in an interface-engineered VO. Herein, we investigate the carrier dynamics in the VO films with anomalous MIT on the basis of time-resolved transient differential reflectivity measurements. Unexpectedly, MIT is decoupled from SPT, in sharp contrast with the case of strain-free VO films: MIT is triggered by bandgap recombination below 75 °C during heating, while intense SPT-induced signal appears separately between 70 °C and 100 °C. The decoupling between MIT and SPT provides insights into the interfacial interactions in VO thin films.