Elastic properties of the Non-Fermi liquid metal $Ce Ru_4 Sb_{12}$ and the Dense Kondo semiconductor $Ce Os_4 Sb_{12}$

TL;DR

This study investigates the elastic properties of CeRu4Sb12 and CeOs4Sb12, revealing distinct behaviors linked to their electronic states and phase transitions, highlighting the coupling between elastic strain and electronic band structures.

Contribution

The paper provides new ultrasonic measurements of elastic constants in CeRu4Sb12 and CeOs4Sb12, elucidating their electronic ground states and coupling mechanisms near the Fermi level.

Findings

CeRu4Sb12 shows no low-temperature softening in elastic constants.

CeOs4Sb12 exhibits elastic softening below 15 K and a phase transition at 0.9 K.

Elastic softening in CeOs4Sb12 is linked to quasiparticle band coupling.

Abstract

We have investigated the elastic properties of the Ce-based filled skutterudite antimonides CeRu$_{4}$Sb$_{12}$ and CeOs$_{4}$Sb$_{12}$ by means of ultrasonic measurements. CeRu$_{4}$Sb$_{12}$ shows a slight increase around 130 K in the temperature dependence of the elastic constants $C$$_{11}$, ($C$$_{11}$-$C$$_{12}$)/2 and $C$$_{44}$. No apparent softening toward low temperature due to a quadrupolar response of the 4$f$-electronic ground state of the Ce ion was observed at low temperatures. In contrast CeOs$_{4}$Sb$_{12}$ shows a pronounced elastic softening toward low temperature in the longitudinal $C$$_{11}$ as a function of temperature ($T$) below about 15 K, while a slight elastic softening was observed in the transverse $C$$_{44}$ below about 1.5 K. Furthermore, CeOs$_{4}$Sb$_{12}$ shows a steep decrease around a phase transition temperature of 0.9 K in both $C$$_{11}$ and$ C$$_{44}$. The elastic softening observed in $C$$_{11}$ below about 15 K cannot be explained reasonably only by the crystalline electric field effect. It is most likely to be responsible for the coupling between the elastic strain and the quasiparticle band with a small energy gap in the vicinity of Fermi level. The elastic properties and the 4$f$ ground state of Ce ions in CeRu$_{4}$Sb$_{12}$ and CeOs$_{4}$Sb$_{12}$ are discussed from the viewpoint of the crystalline electric field effect and the band structure in the vicinity of Fermi level.