Effective Hamiltonian for PrRu4P12 Showing Unconventional Charge Ordering

• Published in: Journal of the Physical Society of Japan 2010-04, Vol.79 (4), p.044704-044704-6
• Main Author: Shiina, Ryousuke
• Format: Article
• Language: English
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Crystal and ligand fields; Electron states; Exact sciences and technology; Level splitting and interactions; Physics
• ISSN: 0031-9015; 1347-4073
• DOI: 10.1143/JPSJ.79.044704

The origin and the nature of the charge ordering in PrRu 4 P 12 are studied theoretically by using a simple model. First, the mixing matrix elements between conduction electrons and Pr 4 f 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.