RESISTIVITY OF THE HIGH-TEMPERATURE METALLIC PHASE OF VO2

Measurements are reported of the electrical resistivity rho(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-Gruneisen theory gives a residual resistivity rho0 = 65 muOMEGA cm and a ratio rho(840 K)/rho0 = 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 lambda = 1.1 and the mean free path l(800 K) = 3.3 angstrom. 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 greater-than-or-equal-to 3. Another possibility is that, in common with the normal state of copper oxide superconductors, metallic VO2 may not be a conventional Fermi liquid.