Multipole Ordering and Fluctuations in f-Electron Systems

TL;DR

This paper explores the role of multipole moments, especially octupole moments, in f-electron systems, revealing their influence on magnetic susceptibility and proposing a microscopic theory for multipole ordering and response functions.

Contribution

It introduces a microscopic approach to analyze multipole ordering and response functions in f-electron systems using a j-j coupling scheme and fluctuation exchange approximation.

Findings

Octupole moments significantly affect magnetic susceptibility.

Deviations from Curie-Weiss law due to dipole-octupole interactions.

Development of a microscopic method for multipole response evaluation.

Abstract

We investigate effects of multipole moments in f-electron systems both from phenomenological and microscopic viewpoints. First, we discuss significant effects of octupole moment on the magnetic susceptibility in a paramagnetic phase. It is found that even within mean-field approximation, the magnetic susceptibility deviates from the Curie-Weiss law due to interactions between dipole and octupole moments. Next, we proceed to a microscopic theory for multipole ordering on the basis of a j-j coupling scheme. After brief explanation of a method to derive multipole interactions from the $f$-electron model, we discuss several multipole ordered phases depending on lattice structure. Finally, we show our new development of the microscopic approach to the evaluation of multipole response functions. We apply fluctuation exchange approximation to the f-electron model, and evaluate multipole response functions.