Theory of intermediate-valence states in Sm compounds

The intermediate-valence states of SmB6 and SmS are described in terms of the periodic Anderson model comprised of the localized 4f multiplet states H-6(5/2) and F-7(0) Of two adjacent configurations 4f(5) and 4f(6); the wide conduction band states represented by the plane wave functions, and the hybridizations between the 4f and the conduction states. We take hole picture and introduce fermi operators representing the states of H-6(5/2) and a bose operator for the F-7(0) Singlet for each Sm site. At low temperatures, the bosons form a condensate, and consequently the fermion states hybridize with the conduction-band states to become itinerant, accompanied with an anisotropic gap structure. The susceptibility is dominated by the Van Vleck contribution from the excited F-7(1) level of 4f(6); while the H-6(5/2) states of 4f(5) gives a small Pauli-type contribution, in good agreement with experimental results.