Multipole Susceptibility of Multiorbital Anderson Model Coupled with Jahn-Teller Phonons

TL;DR

This study explores multipole states in Sm-based skutterudites by analyzing a multiorbital Anderson model coupled with Jahn-Teller phonons, revealing complex multipole behaviors influenced by electron-phonon interactions.

Contribution

It introduces a numerical approach to determine multipole states in a multiorbital Anderson model with Jahn-Teller phonons, highlighting the effects of electron-phonon coupling on multipole susceptibilities.

Findings

Dominant 2u octupole state for $$ ground state without phonons.

Low-temperature phase governed by magnetic fluctuations for $$ doublet ground state.

Mixed multipole state with 4u magnetic and 5u octupole moments when including Jahn-Teller phonons.

Abstract

In order to clarify possible multipole states of Sm-based filled skutterudite compounds, we investigate multipole susceptibility of a multiorbital Anderson model dynamically coupled with Jahn-Teller phonons by using a numerical renormalization group method. Here we take a procedure to maximize the multipole susceptibility matrix to determine the multipole state. When the electron-phonon coupling term is simply ignored, it is found that the dominant multipole state is characterized by 2u octupole for the $\Gamma_{67}^-$ quartet ground state, while the low-temperature phase is governed by magnetic fluctuations for the $\Gamma_5^-$ doublet ground state. When we include the coupling between $f$ electrons in degenerate $\Gamma_{67}^{-}$ ($e_{\rm u}$) orbitals and Jahn-Teller phonons with $E_{\rm g}$ symmetry, the mixed multipole state with 4u magnetic and 5u octupole moments is found to be dominant with significant 3g quadrupole fluctuations at low temperatures.