A theory of strange metals

I present a theory of transport and optical response in quantum materials that is based on the assumption that the motion of the charge carriers obeys the correspondence principle, in the sense that the quantum-mechanically averaged carrier diffusion in time is analogous to the classical case. In bad metals, where wave-like coherence is lost at each hop between neighboring atoms, this leads to strange $T$-linear resistivities with apparently Planckian scattering rates as well as both the stretched Drude and displaced Drude peaks that are commonly observed in optical absorption experiments. The present framework might also indicate a solution to the problem of universal dielectric relaxation in insulators.