Hybridization Effects and Multipole Orders in Pr Skutterudites(Yukawa International Seminar 2004 (YKIS2004) Physics of Strongly Correlated Electron Systems)

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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 F_4-type wave functions. If the weight of the F_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 F_3-type symmetry is found to be stable only as a mixture of O^0_2 and O^2_2 components.
理論物理学刊行会の論文
2006-02-06

Hybridization Effects and Multipole Orders in Pr Skutterudites(Yukawa International Seminar 2004 (YKIS2004) Physics of Strongly Correlated Electron Systems)

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