Theory of Crystalline Electric Field and Kondo Effect in Pr Skutterudites

Abstract

Possible Kondo effect in Pr skutterudite is studied with attention to characteristic features of low-lying crystalline electric field (CEF) levels and the conduction band. A mechanism for the small CEF splitting between a singlet and a triplet is proposed as combination of the point-charge interaction and hybridization of 4f with ligand p states. Provided 4f^3 configurations dominate over 4f^1 as intermediate states, p-f hybridization favors the triplet, while point-charge interaction favors the singlet. For realistic parameters for hybridization as well as 4f^1 and 4f^3 levels, these singlet and triplet can form a nearly degenerate pseudo-quartet. It is found that one of two spin 1/2 objects composing the pseudo-quartet has a ferromagnetic exchange, while the other has an antiferromagnetic exchange with conduction electrons. The magnitude of each effective exchange depends strongly on a parameter characterizing the triplet wave function under the T_h symmetry. It is argued that differences of this parameter among Pr skutterdudites are responsible for the apparent diversity of their physical properties. Numerical renormalization group is used to derive the renormalization flows going toward singlet, doublet, triplet or quaret according to the CEF splitting and exchange interactions.

arXiv comment19 pages, 6 figures, to be published in Special Invited Section (Kondo Effect) of Journal of Physical Society of Japan

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• Sb-NQR probe for multipole degree of freedom in the first Pr-based heavy-fermion superconductor PrOs${}_4$Sb${}_{12}$
• Dynamics of the Singlet-Triplet System Coupled with Conduction Spins -- Application to Pr Skutterudites
• Microscopic Mechanism for Staggered Scalar Order in PrFe4P12
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• Effects of Impurities with Singlet-Triplet Configuration on Multiband Superconductors
• Odd-Parity Crystalline Electric Field and Multipoles in Icosahedral Quasicrystal and Approximant: Magnetic Toroidal and Electric Dipoles in Ce-Based Systems
• Slave Boson Analysis on $f^2$-Configuration System with ${\Gamma }_1$ Singlet Crystalline-Electric-Field Ground State in Cubic Symmetry