Correlated metallic state of vanadium dioxide

The metal-insulator transition and unconventional metallic transport in vanadium dioxide (VO2) are investigated with a combination of spectroscopic ellipsometry and reflectance measurements. The data indicate that electronic correlations, not electron-phonon interactions, govern charge dynamics in the metallic state of VO2. This study focuses on the frequency and temperature dependence of the conductivity in the regime of extremely short mean free path violating the Ioffe-Regel-Mott limit of metallic transport. The standard quasiparticle picture of charge conduction is found to be untenable in metallic VO2.