Thermoelectric power of Cerium and Ytterbium intermetallics
| Autor: | Veljko Zlatić, Claas Grenzebach, I. Milat, B. Horvatić, B. Coqblin, Gerd Czycholl |
|---|---|
| Jazyk: | angličtina |
| Rok vydání: | 2003 |
| Předmět: |
Physics
Ytterbium Condensed matter physics Scattering chemistry.chemical_element Atmospheric temperature range Coupling (probability) thermoelectric power Cerium and Ytterbium intermetallics chemistry Excited state Seebeck coefficient Strongly correlated material Condensed Matter::Strongly Correlated Electrons Atomic physics Anderson impurity model |
| DOI: | 10.1103/physrevb.68.104432 |
| Popis: | The temperature dependence of the thermoelectric power (TEP) of metallic systems with cerium and ytterbium ions exhibits characteristic features which we explain by the Coqblin-Schrieffer model (CSM). We specify a given system by the degeneracy and splitting of the crystal-field (CF) levels, the strength of the exchange and potential scattering, and the number of f electrons or f holes; for cerium and ytterbium ions we assume ${n}_{f}l~1$ and ${n}_{f}^{\mathrm{hole}}l~1,$ respectively. The Kondo temperature ${T}_{K}$ is then generated by the ``poor man's scaling''; it separates a local-moment (LM) from a Fermi-liquid (FL) regime. In the LM regime $(Tg~{T}_{K})$ we calculate the TEP by a renormalized perturbation expansion, in which the exchange coupling J is also renormalized by the poor man's scaling. This gives the TEP with a large peak at high temperatures and a sign change at ${T}_{x}\ensuremath{\simeq}\ensuremath{\alpha}{T}_{K},$ where for parameters used in this paper we have $\ensuremath{\alpha}$ between roughly 2.5 and 10. For ${n}_{f}\ensuremath{\simeq}1$ and large CF splitting, we find a broad temperature range ${T}_{K}\ensuremath{\ll}Tl~{T}_{x},$ in which the TEP of the CSM is negative. In the FL regime $(Tl~{T}_{K})$ we neglect the excited CF states, reduce the CSM to an effective spin-degenerate exchange model, map it on an effective spin-degenerate Anderson model, and calculate the TEP by an expansion in terms of $U\ensuremath{\propto}1/J.$ For cerium ions ${(n}_{f}l~1)$ we obtain in this way the TEP which follows for $T\ensuremath{\ll}{T}_{K}$ a linear FL law, attains at about ${T}_{K}/2$ a positive maximum, and changes sign above ${T}_{K}.$ The results pertaining to ytterbium ions ${(n}_{f}^{\mathrm{hole}}l~1)$ are obtained by reflecting the ${n}_{f}l~1$ curves on the temperature axis. The overall results obtained for the CSM in such a way explain the essential features of the temperature, pressure, and doping dependence of the TEP in cerium and ytterbium systems. Unfortunately, neither our high-temperature nor the low-temperature expansion provide the details or locate the minimum of the negative TEP which we find in the transition region between the FL and LM regimes. |
| Databáze: | OpenAIRE |
| Externí odkaz: |
|