Decoupling between metal-insulator transition and structural phase transition in an interface-engineered VO2.

The coupling between the metal-insulator transition (MIT) and the structural phase transition (SPT) in VO2has 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 VO2is 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 VO2. Herein, we investigate the carrier dynamics in highly strained VO2films 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 VO2films: MIT is triggered by bandgap recombination below 75oC during heating, while intense SPT-induced signal appears separately between 70oC and 100oC. The decoupling between MIT and SPT provides insights into the interfacial interactions in VO2thin films.