Hybridization Effects and Multipole Orders in Pr Skutterudites
Abstract
Theoretical account is given of 4f-electron dynamics and multipole orders in Pr skutterudites with particular attention to (i) mechanism of the crystalline electric field (CEF) splitting leading to a pseudo-quartet ground state; (ii) Kondo effect due to exchange interactions involving the pseudo-quartet; (iii) multipole orders in the lattice of the pseudo-quartet in magnetic field. Competition between the point-charge interaction and hybridization between 4f and conduction electrons is identified as the key for controlling the CEF splitting. It is found that one of two pseudo-spins forming the pseudo-quartet has a ferromagnetic exchange, while the other has an antiferromagnetic exchange with conduction electrons. The Kondo effect is clearly seen in the resistivity calculated by the NCA, provided the low-lying triplet above the singlet is mainly composed of the Γ_4-type wave functions. If the weight of the Γ_5-type is large in the triplet, the Kondo effect does not appear. This difference caused by the nature of the triplet explains the presence of the Kondo effect in PrFe_4P_{12}, and its absence in PrOs_4Sb_{12}. By taking the minimal model with antiferro-quadrupole (AFQ) and ferro-type intersite interactions for dipoles and octupoles between nearest-neighbors, the mean-field theory reproduces the overall feature of the multiple ordered phases in PrFe_4P_{12}. The AFQ order with the Γ_3-type symmetry is found to be stable only as a mixture of O_2^0 and O_2^2 components.
- Publication:
-
Progress of Theoretical Physics Supplement
- Pub Date:
- 2005
- DOI:
- 10.1143/PTPS.160.134
- arXiv:
- arXiv:cond-mat/0506788
- Bibcode:
- 2005PThPS.160..134K
- Keywords:
-
- Condensed Matter - Strongly Correlated Electrons
- E-Print:
- 21 pages, to be published in proc. YKIS2004