Coqblin-Schrieffer, Hamiltonian

Elcs Coqblin-Schrieffer Hamiltonian R lattice vector... 

For —Sf A, U A and U + 2ef = 0 the Anderson Hamiltonian, eq.(1), can be transformed into the Coqblin-Schrieffer (CS) Hamiltonian. In this Kondo limit charge fluctuations are completely suppressed and the model describes an effective 4f-electron spin j which interacts via exchange with the conduction electrons... 

For the non-symmetrical Anderson model with C/ + 2ef 0, one has in the Coqblin Schrieffer and Kondo Hamiltonians in addition to the exchange a potential scattering term. The Kondo resonance is no longer at the Fermi energy ep = 0 but is shifted. This shift leads to a smaller resistivity p(T), the maximum of which, however, is still at T = 0. The potential scattering has a dramatic effect on the thermoelectric power, which vanishes in the symmetric case C/ + 2ef = 0, but has a huge peak near 7k for C/ 4- 2ef 0. 

As described by Liu (1961) the nature of the exchange interaction changes when the energy required to promote an electron from the conduction band into the 4f band is small. In this case the admixture interaction between conduction and 4f electrons must be taken into account. This interaction leads to "an effective attractive sp-f exchange interaction of the Schrieffer-Wolff kind though the form of the Hamiltonian is still given by eq. (19). Such admixture interactions are applicable to Ce and Yb alloys (see Coqblin and Blandin, 1968) and lead to a Kondo effect. 

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