The slave boson mean-field theory of two-conduction-band Kondo alloys

A self-consistent coherent potential approximation calculation of the density of states (DOS) for a two-conduction-band alloy model has been given in the framework of the slave boson mean-field theory. The results show that, with increasing concentration of Kondo impurities, the f-electron DOS near the Fermi level will gradually change from a resonance peak for the dilute system into a coherent f band with a pseudo-gap for the concentrated system. Simultaneously, there appears a narrow valley for the DOS of the conduction electrons in the vicinity of the Fermi level. These results can be used to explain why the low-temperature thermoelectric power of the system changes from negative values to positive values as the system transforms from the Kondo impurity to the Kondo lattice. The authors also demonstrate that the Kondo temperature does not vary with the concentration of the alloy system. This is in agreement with the recent experimental results for heavy-fermion alloys.