Abstract
The nature of the valence-fluctuation problem is described, and motivations are given for an Anderson lattice model Hamiltonian. A simple trial wavefunction is posed for the ground state, and the variational problem is solved. This demonstrates clearly that there is no Kondo-like divergence; the present “concentrated Kondo” problem is thus more simple mathematically than the single-impurity problem. Elementary excitations are studied by the Green's function techniques of Zubarev and Hubbard. Quenching of local moments and a large specific heat are found at low temperatures. The quasiparticle spectrum exhibits a gap, but ϵf does not lie in this gap. The insulationlike feature of SmB6, SmS, and TmSe at very low temperatures is explained in terms of a strongly reduced mobility for states near the gap, and reasons are given why this feature is not observed in other valence-fluctuation compounds.
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