Toward Identification of Order Parameters in Skutterudites - a Wonderland of Strong Correlation Physics -

Abstract

Current status is described toward identifying unconventional order parameters in filled skutterudites with unique ordering phenomena. The order parameters in PrFe${}_4$P${}_{12}$ and PrRu${}_4$P${}_{12}$ are discussed in relation to associated crystalline electric field (CEF) states and angular form factors. By phenomenological Landau analysis, it is shown that a scalar order model explains most properties in both PrFe${}_4$P${}_{12}$ and PrRu${}_4$P${}_{12}$ with very different magnetic properties. In particular, the highly anisotropic susceptibility induced by uniaxial pressure in PrFe${}_4$P${}_{12}$ is explained in terms of two types of couplings. In the case of SmRu${}_4$P${}_{12}$, the main order parameter at low field is identified as magnetic octupoles. A microscopic mechanism is proposed how the dipole and octupole degrees of freedom mix under the point group $T_h$ of skutterudites.

To be published in Proc. International Conference on New Quantum Phenomena in Skutterudite and Related Systems (Suppl. J. Phys. Soc. Jpn 78, 2008)

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