Relationship between the thermopower and entropy of strongly correlated electron systems
A number of recent experiments report the low-temperature thermopower $α$ and specific heat coefficients $γ=C_V/T$ of strongly correlated electron systems. Describing the charge and heat transport in a thermoelectric by transport equations, and assuming that the charge current and the heat current densities are proportional to the number density of the charge carriers, we obtain a simple mean-field relationship between $α$ and the entropy density $\cal S$ of the charge carriers. We discuss corrections to this mean-field formula and use results obtained for the periodic Anderson and the Falicov-Kimball models to explain the concentration (chemical pressure) and temperature dependence of $α/γT$ in EuCu$_2$(Ge$_{1-x}$Si$_x$)$_2$, CePt$_{1-x}$Ni$_x$, and YbIn$_{1-x}$Ag${_x}$Cu$_4$ intermetallic compounds. % We also show, using the 'poor man's mapping' which approximates the periodic Anderson lattice by the single impurity Anderson model, that the seemingly complicated behavior of $α(T)$ can be explained in simple terms and that the temperature dependence of $α(T)$ at each doping level is consistent with the magnetic character of 4{\it f} ions.