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

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 $Γ_{67}^-$ quartet ground state, while the low-temperature phase is governed by magnetic fluctuations for the $Γ_5^-$ doublet ground state. When we include the coupling between $f$ electrons in degenerate $Γ_{67}^{-}$ ($e_{\rm u}$) 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.

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