Thermoelectric power of concentrated Kondo systems.

Abstract

The thermopower of concentrated Kondo systems based on Ce-Cu, Ce-B, and Yb-Cu intermetallic compounds doped with nonmagnetic impurities like Al, Ag, Au, and Ga, is discussed using the single-impurity Anderson model with more than one scattering channel. Interference between the resonant and nonresonant scattering is important for relating the theory to the experimental data. Correlation effects are present in the resonant channel and are accounted for by a numerical renormalization-group method. The large enhancement of the thermopower over the free-electron values reflects the renormalization of the characteristic energy scale of the elementary excitations from the Fermi energy, ${\mathrm{\ensuremath{\epsilon}}}_{\mathit{F}}$, to the Kondo energy, ${\mathit{T}}_{\mathit{K}}$. The characteristic shape of the experimental curves reflects the change in the structure of the low-energy excitations as the temperature passes through the Kondo temperature. The observed sensitivity of the sign of the thermopower to small changes of the local environment around the magnetic ions is attributed to the interference between resonant and nonresonant scattering.