Microscopic and Nanoscale Perspective of the Metal-Insulator Phase Transitions of VO2: Some New Twists to an Old Tale

The peculiarities in the electronic structure of the seemingly simple binary vanadium oxide VO2, as manifested in a pronounced metal insulator phase transition in proximity to room temperature, have made it the subject of extensive theoretical and experimental investigations over the last several decades. We review some recent advances in theoretical treatments of strongly correlated systems along with ultrafast measurements of VO2 samples that provide unprecedented mechanistic insight into the nature of the phase transition. Scaling VO2 to nanoscale dimensions has recently been possible and has allowed well-defined VO2 nanostructures to serve as model systems for measurements of intrinsic properties without obscuration from grain boundary connectivities and domain dynamics. Geometric confinement, substrate interactions, and varying defect densities of VO2 nanostructures give rise to an electronic and structural phase diagram that is substantially altered from the bulk. We postulate that design principles deduced from fundamental understanding of phase transitions in nanostructures will allow the predictive and rational design of systems with tunable charge and spin ordering.