Study of Localized Character of 4f Electrons and Ultrasonic Dispersions in SmOs4Sb12 by High-Pressure High-Frequency Ultrasonic Measurements

TL;DR

This study investigates how high-pressure ultrasonic measurements reveal the transition of 4f electrons from delocalized to localized in SmOs4Sb12, highlighting implications for non-Fermi liquid behavior and electron-phonon interactions.

Contribution

It provides new insights into the pressure-induced localization of 4f electrons and their coupling with rattling phonons in SmOs4Sb12, using high-frequency ultrasonic techniques.

Findings

4f electrons localize above 0.7 GPa

Non-Fermi liquid state appears between 0.5-1.5 GPa

Ultrasonic dispersion due to rattling phonons changes with pressure

Abstract

We present high-frequency ultrasonic measurements on the filled skutterudite SmOs$_4$Sb$_{12}$ under hydrostatic pressure. The results clarify that the 4$f$ electrons in this compound transform from delocalized at ambient pressure to localized at high pressures with a crossover pressure of approximately 0.7 GPa. This drastic change in the 4$f$ electrons under pressure is apparently related to the non-Fermi liquid state, which appears in an intermediate-pressure range of 0.5-1.5 GPa. The results or our analysis strongly suggest that the ferro-octupolar interaction becomes dominant at high pressure. Moreover, we report the pressure dependence of the ultrasonic dispersion, which is due to rattling, over a wide range of ultrasonic frequencies up to 323 MHz. The drastic change in the ultrasonic dispersions and the frequency dependent elastic anomaly in the $C_{11}$ mode at lower temperatures imply a possible coupling between rattling phonons and 4$f$ electrons.