Strange metals, from phenomenology to models: reconciling spectroscopy, thermodynamics and transport

I will discuss the remarkable implications of a `Planckian' T-linear scattering rate for optical spectroscopy and thermoelectric properties, and confront these predictions to measurements of the Seebeck coefficient and optical response of cuprates in the strange metal regime. I will show how the scaling of the optical conductivity can be reconciled with resistivity and specific heat measurements. I will also review recent works which support the existence of a quantum phase transition at a critical doping doping between two metallic phases in models of a doped Mott insulator with random exchange. At this quantum critical point, the Fermi surface undergoes a volume change and `Planckian' behaviour is found.