Resistivity of the high-temperature metallic phase of VO₂

Measurements are reported on the electrical resistivity ρ(T) along the c axis of a single crystal of VO₂, from the metal-insulator transition at T=333 K up to 840 K. The temperature dependence is very linear, and a fit to Bloch-Grüneisen theory gives a residual resistivity ρ₀=65 μΩ cm and a ratio ρ(840 K)/ρ₀=8. With the help of a local-density-approximation band-structure calculation, we further pursue the conventional (Bloch-Boltzmann) interpretation by extracting the electron-phonon coupling constant λ=1.1 and the mean free path l(800 K)=3.3 Å. The short mean free path implies that the conventional interpretation is internally inconsistent. The most likely explanation is that unknown internal damage (e.g., cracks) has altered the effective cross section of the sample, causing the measured resistivity to be overestimated by a factor ≥3. Another possibility is that, in common with the normal state of copper oxide superconductors, metallic VO₂ may not be a conventional Fermi liquid.