Theory of Intermediate-Valence States in Sm Compounds

The intermediate-valence states of SmB 6 and SmS are described in terms of the periodic Anderson model comprised of the localized 4 f multiplet states 6 H 5/2 and 7 F 0 of two adjacent configurations 4 f 5 and 4 f 6 , the wide conduction band states represented by the plane wave functions, and the hybridizations between the 4 f and the conduction states. We take hole picture and introduce fermi operators representing the states of 6 H 5/2 and a bose operator for the 7 F 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 7 F 1 level of 4 f 6 , while the 6 H 5/2 states of 4 f 5 gives a small Pauli-type contribution, in good agreement with experimental results.