Disentangling pre-transitional fluctuations in metallic VO2

Abstract

VO2 features concomitant structural and metal-insulator transitions. This poses a challenge for understanding the underlying mechanism: is the transition triggered by a structural or by an electronic instability? The two scenarios are expected to produce very different pre-transitional fluctuations above TC. By combining magnetic susceptibility, IR reflectivity and X-ray diffuse scattering measurements, we observe that metallic VO2 features strong electronic and structural fluctuations towards the insulating monoclinic phase. By measuring resonant diffuse X-ray scattering across the Vanadium K-edge, we search for a potential decoupling between electronic and structural ordering in these fluctuations, finding no evidence of it. While our results do not completely rule out pure electronic fluctuations, they constrain them, favoring the interpretation that the VO2 metal-insulator transition is triggered by a structural instability. Our work offers a novel approach to solve similar problems in other strongly correlated systems.