Study of localized character of 4/ electrons and ultrasonic dispersions in SmOs_4Sb_(12) by high-pressure high-frequency ultrasonic measurements

摘要

We present high-frequency ultrasonic measurements on the filled skutterudite SmOs_4Sb_(12) under hydrostatic pressure. The results clarify that the 4f 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 4f 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 C_(11) mode at lower temperatures imply a possible coupling between rattling phonons and 4f electrons.