Atomic dynamics of low-lying rare-earth guest modes in heavy fermion filled skutteruditesROs4Sb12(

Abstract

The atomic dynamics of the guest modes in heavy fermion filled skutterudites ROs 4 Sb 12 were investigated by inelastic x-ray scattering. Comparison of the phonon dispersion relations for the filled skutterudite SmOs 4 Sb 12 with those for the unfilled skutterudite IrSb 3 indicates that the guest modes in filled skutterudites are observed as additional modes in the unfilled skutterudites. The dispersion relations for IrSb 3 and SmOs 4 Sb 12 agree reasonably well with the results obtained by ab initio calculations for IrSb 3 and LaOs 4 Sb 12 , respectively. The rare-earth dependence of the inelastic x-ray scattering spectrum in the series of ROs 4 Sb 12 compounds is difficult to interpret in terms of changes in the atomic mass and electron number of the rare-earth atom inserted into the Sb cage. The combination of inelastic x-ray scattering and x-ray absorption spectroscopy reveals a correlation between the guest mode energy and the guest free space in these compounds. The rare-earth dependence of the inelastic x-ray scattering spectrum indicates the mediation of heavy fermion behavior by the atomic motion of the guest in some ROs 4 Sb 12 compounds and the electron-phonon coupling between the guest modes with 4f -electrons and conduction electrons in the series of ROs 4 Sb 12 compounds.

Rare-Earth Atomic Motion in RBe13 (R: La, Pr, Sm)

“…Meanwhile, the discrepancy between the phonon energies observed in the present work and estimated from the force constant at the 8a site in LaBe 13 implies that the phonon energy correlates with the free space at the 8a site which affects anharmonic potential. Similar discrepancy due to the free space at the guest atoms was reported in a series of filled skutterudites RFe 4 P 12 and ROs 4 Sb 12 [20,39]. Further investigations are required to conclude the correlation between the discrepancy between the phonon energy determined by IXS and NRIS and the Einstein temperature estimated by specific heat measurements and diffraction experiments in a series of RBe 13 .…”

“…Therefore, other factors to suppress the phonon energy of the rare-earth is required. Since similar rare-earth dependence of the rare-earth modes was found in filled skutterudites ROs 4 Sb 12 [20], one of the possible reasons for the rare-earth dependence is caused by anharmonic potential. .…”

“…Phonon dispersions were reported in other cage-structured compounds such as rare-earth hexaborides [13,14], filled-skutterudites [15][16][17][18][19][20], and clathrates [21,22]. These compounds have nearly flat dispersions of low-lying optical modes due to a guest atom in the cage and anti-crossings between the acoustic and low-lying optical modes.…”

Low-temperature x-ray crystal structure analysis of the cage-structured compounds MBe13(M=La,Sm,and U)

“…The characteristic energy of the low-energy phonon mode appears to have no relation to the value of γ , implying that the HF state for UBe 13 may not originate from the presence of the low-energy phonon mode. However, it has also been suggested that an electron-phonon coupling between the conduction electrons and the low-energy Einstein phonon also plays an important role in formation of the phonon-mediated HF state [36][37][38]. Therefore, it is necessary to check the strength of the electronphonon coupling in the MBe 13 systems to reveal the role of the low-energy phonon mode in the HF state for UBe 13 .…”

Influence of Lattice Dynamics on Electronic Properties in Rare-Earth Filled-Skutterudites

“…20 Phonon dispersion relations in filled-skutterudite SmOs4Sb12 upper paanel and unfilled skutterudite IrSb3 lower panel at room temperature determind by inelastic X-ray scattering. 20 Inelastic X-ray scattering spectra at a longitudinal H points and b transverse N points in ROs4Sb12. …”