T -square electric resistivity and its thermal counterpart in RuO 2

We present a study of low-temperature electric and thermal transport in ${\mathrm{RuO}}_{2}$, a metallic oxide which has attracted much recent attention. Careful scrutiny of electric resistivity reveals a quadratic temperature dependence below $\ensuremath{\sim}20$ K undetected in previous studies of electronic transport in this material. The prefactor of this ${T}^{2}$ resistivity, given the electronic specific heat, corresponds to what is expected by the Kadowaki-Woods scaling. The variation of its amplitude across four different samples is negligible despite an eightfold variation of residual resistivity. There is also a ${T}^{5}$ resistivity due to scattering by phonons. By measuring thermal conductivity $\ensuremath{\kappa}$ at zero field and at 12 T, we separate its electronic and phononic components and find that the former respects the Wiedemann-Franz law at zero temperature and deviates downward at finite temperature. The latter corresponds to a threefold discrepancy between the prefactors of the two (thermal and electric) $T$-square resistivities. Our results, establishing ${\mathrm{RuO}}_{2}$ as a weakly correlated Fermi liquid, provide input for the ongoing theoretical attempt to give a quantitative account of electron-electron scattering in metallic oxides starting from first principles.