Photo-induced metal-like phase of VO 2 with sub-ns recovery
Résumé
VO2 is a unique insulator-metal transition material with a near room temperature transition temperature that is a major focus of interest in burgeoning fields such as all-optical devices and neuromorphic computing. The photo-induced insulator-metal transition of VO2 is of particular interest for the development of ultrafast optical devices; however, the recovery dynamics of VO2 after a photo-induced insulator-metal transition must be better understood. Here, the time-resolved differential transmittance of VO2 after excitation by an ultrashort pump laser pulse and the recovery of VO2 back to its equilibrium state are studied. For pump laser fluences in a mid-fluence region, which is found to match the mid-fluence region for the recently discovered photo-induced monoclinic metal phase of VO2, a strong non-linear change in the differential transmittance of VO2 with fast recovery is discovered. In the mid-fluence region, a 15 nm VO2 thin-film is shown to have a differential transmittance at the saturation value of 14%, while exhibiting full recovery in less than 600 ps. These results demonstrate that the large changes in the optical properties of VO2 associated with its photo-induced insulator-metal transition can recover on sub-ns timescales, allowing for efficient GHz speed all-optical and neuromorphic computing devices using VO2.