Magnetic-Field-Independent Ultrasonic Dispersions in the Magnetically Robust Heavy Fermion System SmOs4Sb12

TL;DR

This study reveals magnetic-field-independent ultrasonic dispersions in SmOs4Sb12, suggesting a magnetically insensitive heavy fermion state linked to a novel local charge degree of freedom, with implications for understanding heavy fermion systems.

Contribution

It reports the discovery of magnetic-field-independent ultrasonic dispersions in SmOs4Sb12 and links these to a possible local charge degree of freedom in heavy fermion systems.

Findings

Ultrasonic dispersions at ~15 K and ~53 K follow Debye-type behavior.

Dispersions remain unchanged under magnetic fields up to 10 T.

Activation energies are 105 K and 409 K, with the latter being the highest in Sb-based skutterudites.

Abstract

Elastic properties of the filled skutterudite compound SmOs$_4$Sb$_{12}$ have been investigated by ultrasonic measurements. The elastic constant $C_{11}(\omega)$ shows two ultrasonic dispersions at $\sim$15 K and $\sim$53 K for frequencies $\omega$ between 33 and 316 MHz, which follow a Debye-type formula with Arrhenius-type temperature-dependent relaxation times, and remain unchanged even with applied magnetic fields up to 10 T. The corresponding activation energies were estimated to be $E_2$ = 105 K and $E_1$ = 409 K, respectively. The latter, $E_1$, is the highest value reported so far in the Sb-based filled skutterudites. The presence of magnetically robust ultrasonic dispersions in SmOs$_4$Sb$_{12}$ implies a possibility that an emergence of a magnetically insensitive heavy fermion state in this system is associated with a novel local charge degree of freedom which causes the ultrasonic dispersion.