Abstract
We present high-frequency ultrasonic measurements on the filled skutterudite under hydrostatic pressure. The results clarify that the 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 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 of 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 mode at lower temperatures imply a possible coupling between rattling phonons and electrons.
- Received 30 March 2016
- Revised 1 August 2016
DOI:https://doi.org/10.1103/PhysRevB.94.085142
©2016 American Physical Society