Antiferro-Hexadecapole Scenario for Metal–Insulator Transition in PrRu₄P₁₂

Abstract

A theory of metal–insulator transition in PrRu 4 P 12 is developed from a microscopic point of view, based on j – j coupling scheme. For the metal–insulator transition, we propose antiferro-hexadecapole order without breaking local symmetry. It is shown that the hexadecapole ordered state appears in the case that the ground state of Pr-ion is Γ 1 singlet, and conduction electrons dominantly belong to Γ 5 in T h point group. For half-filled conduction band, system becomes insulator in the ordered state due to gap formed by the antiferro-hexadecapole moment. The present scenario provides reasonable explanation for experimental results of PrRu 4 P 12 .