Analysis of - model for octupole ordering in NpO

Kubo, Katsunori ; Hotta, Takashi

In order to examine the origin of octupole ordering in NpO, we propose a microscopic model constituted of neptunium and oxygen orbitals. To study multipole ordering, we derive effective multipole interactions from the - model by using the fourth-order perturbation theory in terms of - hopping integrals. Analyzing the effective model numerically, we find a tendency toward antiferro-octupole ordering.