Theory of Low-Temperature Magneto-Transport in Unconventional Charge Order Phase of Skutterudite PrRu4P12

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The skutterudite PrRu4P12 exhibits a metal--insulator transition at 63 K which is known as a consequence of an unconventional charge order (CO) transition. In this paper, the origin of a giant magneto-transport (GMT) in the CO phase at low temperatures is studied theoretically. First, we introduce an effective low-energy model in the well-developed CO phase, in which a small number of conduction electrons in the pseudo-gap state are coupled magnetically with the degenerate f electron triplet states on one of the sublattices. Then, we formulate the transport equation for the conduction electrons by considering inelastic scattering due to the magnetic interaction with the triplet, and solve it within the relaxation time approximation. It is shown that the characteristic temperature and magnetic field dependences of the resistivity and the Hall effect in this material are reproduced well with a reasonable choice of the model parameters. In particular, the strength of the magnetic interaction estimated in this study is quite consistent with the one expected from the microscopic p--f hybridization model. Contributions of the exchange field and the field-dependent relaxation time to the GMT are discussed through quantitative comparisons with the experiments. The effect of the hyperfine coupling between the triplet and the nuclear spin, which has been shown to play a crucial role below 0.3 K, is also discussed.
2011-09-15