Evidence for Undoped Weyl Semimetal Charge Transport in $Y_{2}Ir_{2}O_{7}$.

Weyl fermions scattering from a random Coulomb potential are predicted to exhibit resistivity versus temperature $\rho \space \alpha \space T^{-4}$ in a single particle model. Here we show that, in closed environment-grown polycrystalline samples of $Y_{2}Ir_{2}O_{7}$, $\rho = \rho_{0} T^{-4}$ over four orders of magnitude in $\rho$. While the measured prefactor, $\rho_{0}$, is obtained from the model using reasonable materials parameters, the $T^{-4}$ behavior extends far beyond the model's range of applicability. In particular, the behavior extends into the low-temperature, high-resistivity region where the Ioffe-Regel parameter, $k_{T} \ell \ll 2\pi$. Strong on-site Coulomb correlations, instrumental for predicting a Weyl semimetal state in $Y_{2}Ir_{2}O_{7}$, are the possible origin of such "bad" Weyl semimetal behavior.