Bad metallic transport in a modified Hubbard model
Abstract
Strongly correlated metals often display anomalous transport, including T-linear resistivity above the Mott-Ioffe-Regel limit. We introduce a tractable microscopic model for such bad metals, by supplementing the well-known Hubbard model --- with hopping t and on-site repulsion U --- with a `screened Coulomb' interaction between charge densities that decays exponentially with spatial separation. This interaction entirely lifts the extensive degeneracy in the spectrum of the t=0 Hubbard model, allowing us to fully characterize the small t electric, thermal and thermoelectric transport in our strongly correlated model. Throughout the phase diagram we observe T-linear resistivity above the Mott-Ioffe-Regel limit, together with strong violation of the Weidemann-Franz law and a large thermopower that can undergo sign change. At intermediate temperatures t kB T U, the approximate T-linear resistivity arises from a cancellation between the nontrivial temperature dependence of both diffusivities and thermodynamic susceptibilities, as observed in recent transport experiments on cold atomic gases.