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

TL;DR

This paper explores unconventional order parameters in skutterudites, proposing models and mechanisms that explain diverse magnetic and electronic phenomena in these strongly correlated materials.

Contribution

It introduces a scalar order model for PrFe$_4$P$_{12}$ and PrRu$_4$P$_{12}$, and proposes a microscopic mechanism for dipole and octupole mixing in skutterudites.

Findings

Scalar order model explains properties of PrFe$_4$P$_{12}$ and PrRu$_4$P$_{12}$

Anisotropic susceptibility in PrFe$_4$P$_{12}$ explained by couplings

Magnetic octupoles identified as main order in SmRu$_4$P$_{12}$

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.