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Hybridization effects and multipole orders in Pr skutterudites

Y. Kuramoto·J. Otsuki·A. Kiss·H. Kusunose
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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 andhybridization 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 inPrFe$_4$P$_{12}$, and its absence in PrOs$_4$Sb$_{12}$.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$_4$P$_{12}$. 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.

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Y. Kuramoto, J. Otsuki, A. Kiss, H. Kusunose. 2005-06-30. Hybridization effects and multipole orders in Pr skutterudites. https://doi.org/10.1143/ptps.160.134

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