Microscopic Aspects of Multipole Properties of Filled Skutterudites

TL;DR

This paper investigates the low-temperature multipole states of Nd-based filled skutterudites using a multiorbital Anderson model and numerical renormalization group, revealing dominant magnetic and octupole multipole characteristics and their interactions with phonons.

Contribution

It introduces a procedure to identify dominant multipole states and explores the effects of electron-phonon coupling on multipole fluctuations in skutterudites.

Findings

Dominant multipole state is a mixture of 4u magnetic and 5u octupole moments.

Secondary state characterized by 2u octupole.

Quadrupole fluctuations are enhanced by electron-phonon interactions.

Abstract

We discuss low-temperature multipole states of Nd-based filled skutterudites by analyzing a multiorbital Anderson model with the use of a numerical renormalization group method. In order to determine the multipole state, we take a procedure to maximize the multipole susceptibility matrix. Then, it is found that the dominant multipole state is characterized by the mixture of 4u magnetic and 5u octupole moments. The secondary state is specified by 2u octupole. When we further take into account the coupling between $f$ electrons in degenerate $\Gamma_{67}^{-}$ ($e_{\rm u}$) orbitals and dynamical Jahn-Teller phonons with $E_{\rm g}$ symmetry, quadrupole fluctuations become significant at low temperatures in the mixed multipole state with 4u magnetic and 5u octupole moments. Finally, we briefly discuss possible relevance of the present results to actual Nd-based filled skutterudite compounds.