Insights into the anomalous thermal properties of VO2 from synchrotron spectromicroscopy

Within the last year there have been reports on two distinct anomalous behaviors of the thermal conductivity of VO2 across its insulator-metal transition, namely: (1) a violation of the Wiedemann Franz law and (2) a giant peak in thermal conductivity during the transition. These have not been captured by physical models, and an understanding of their origin requires in situ probing of both the electronic and structural transitions in VO2 with very high spatial and thermal resolution. Here we performed temperature-controlled scanning X-ray absorption spectromicroscopy (SXASM), using synchrotron radiation with <30 nm spatial resolution, on single crystal VO2 that exhibited these anomalies in thermal conductivity. SXASM revealed distinct signatures of the Mott electronic transition and the Peierls structural distortion, which occurred at slightly different temperatures, with the electronic transition occurring first. These results are combined with measurements of thermal conductivity, Seebeck coefficient, and electrical conductivity. We juxtapose these multi-dimensional data sets to shine light on possible correlations between the different transitions and the anomalous changes in VO2 thermal
properties.