Bad Metals and Planckian Metals: DMFT, SYK and physical realisations

Many materials with strong electronic correlations display metallic-like resistivity up to very high temperature, with values exceeding the Mott-Ioffe-Regel (MIR) criterion (`bad metals'). Understanding transport in this regime, in relation to spectroscopic probes such as optical conductivity and ARPES, raises the fundamental question of transport in regimes where long-lived quasiparticles may not exist. Recently, cold atomic gases in optical lattices have offered a beautiful experimental platform to investigate this question without the intervening effect of phonons. Even more challenging is the crossover into a `strange metal' regime at lower temperatures, in which resistivity becomes smaller than the MIR value and the scattering rate obey Planckian behavior with linear dependence on temperature. I will review recent work on these questions in the context of Dynamical Mean Field Theory and Sachdev-Ye-Kitaev models, as well as other analytical and computational approaches, assessing what is established at this point and which questions are still open.