Effective Hamiltonian for PrRu4P12 Showing Unconventional Charge Ordering

概要

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The origin and the nature of the charge ordering in PrRu4P12 are studied theoretically by using a simple model. First, the mixing matrix elements between conduction electrons and Pr 4f states are examined to show that the magnitude of the mixing depends sensitively on the crystal-field (CF) levels. Then, taking the simplest case in which $\Gamma_{1}$ is the CF ground state and $\Gamma_{4}^{(2)}$ is a low-lying CF excited state in the normal phase, we derive an effective Hamiltonian for both the charge and spin degrees of freedom. As expected, it results in a two-sublattice charge ordering assisted by the nesting of conduction band, where $\Gamma_{4}^{(2)}$ becomes the ground state on one of the sublattices. The magnitude of the interaction between $\Gamma_{4}^{(2)}$ triplets can be estimated within the present model; it turns out to be very weak, suggesting that $\Gamma_{4}^{(2)}$ triplets behave as almost free even at low temperatures.
2010-04-15