Characteristics of hybridization and multipole orders of 4f-electrons in Pr skutterudites are explained in terms of a pseudo-quartet composed of crystalline electric field (CEF) singlet and the triplet. It is shown that the contrasting behaviors observed in PrFe4P12 and PrOs 4Sb12 are ascribed to the difference in triplet wave functions and the CEF splittings. Since a macroscopic degeneracy remains even in the ordered phase with the Γ3-type antiferro-quadrupole (AFQ) order, a model with strong AFQ fluctuation and static monopole/hexadecapole order is proposed for PrFe4P12. The remaining cubic symmetry explains qualitatively the behavior of staggered magnetization observed by NMR and neutron scattering. For identification of possible hexadecapole orders in PrFe4P12 and PrRu4P12, eightfold intensity pattern is predicted in the azimuthal angle scan of resonant X-ray scattering. In PrOs4Sb12, the ferromagnetic exchange coupling with the conduction band does not lead to magnetic Kondo effect, but a momentum-dependent quadrupole coupling can give rise to enhanced effective mass, which should be sensitive to disorder.
- Quadrupole order
- Quantum fluctuation
- Resonant X-ray scattering
ASJC Scopus subject areas
- General Physics and Astronomy