Universal thermopower of bad metals

Transport properties of strongly correlated materials, such as vanadates, cobaltates, cuprates, Kondo semiconductors, and organic salts are poorly understood, despite an overwhelming amount of experimental data. One common feature of these vastly different materials is that they are formed by doping the parent compound away from a Mott-Hubbard insulating state. Starting from this observation, and the general properties of the transport relaxation time of a doped Mott-Hubbard systems, we calculate the transport coefficients from the Kubo formula. Our analysis shows that the resistivity and thermopower of such systems exhibit simple universal features which depend on the concentration of the charge carriers.