Thermopower as a signature of quantum criticality in heavy fermions

We present a series of arguments showing that the Seebeck coefficient can be used as a decisive experiment to characterize the nature of the quantum-critical point (QCP) in heavy fermion compounds. Being reactive almost exclusively to the presence of delocalized entropic carriers, the Seebeck coefficient shows a drastic collapse at the Kondo breakdown QCP, as the reconstruction of the Fermi surface takes place. In contrast, around a spin-density-wave QCP, the Seebeck coefficient is broadly symmetric. We discuss the possibility of a change of sign at the QCP, the characteristic variation in vertical bar S/T vertical bar with temperature and external parameter, as well as the capacity of the Seebeck coefficient to distinguish between localized and itinerant antiferromagnetism. Suggestions of experiments are given in the case of four nonconventional compounds: YbRh2Si2, Ce(Mn)In-5, CeCu6-xAux, and URu2Si2.