A theoretical study of the thermoelectric power in heavy fermion systems

We present theoretical models which can account for the thermoelectric power (TEP) of metallic Kondo systems and in particular the compounds with Cerium or Ytterbium. At temperatures much above the Kondo temperature T_k, which is very small typically of order of some K, Kondo Ce or Yb compounds are well described by the Coqblin-Schrieffer model (CSM) including crystal field (CF) effects and using renormalized exchange integrals. Below T_k they have a "heavy fermion" character which is well accounted for by the Anderson model. We obtain, above T_k, the TEP with a large positive (negative) peak for Ce (Yb) compounds mainly due to the exchange scattering on the full CF multiplet and find that the TEP changes sign for temperatures approaching T_k. Below T_k, we obtain another positive (negative) peak for the TEP of Ce (Yb) compounds due to the Kondo scattering on the lowest CF level. We can present an explanation of many TEP curves for Ce compounds, like CeAl₃ which have two positive peaks at very small and large temperatures and, in some cases, negative values in between. A brief review of the TEP curves in anomalous rare-earth systems and the possibility of getting very large values of the TEP in strongly correlated electron systems are finally discussed.