No abstract

We present high-frequency ultrasonic measurements on the filled skutterudite SmOs4Sb12 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 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 C11 mode at lower temperatures imply a possible coupling between rattling phonons and 4f electrons.

No abstract

We performed simultaneous measurements of the elastic constant C 11 and electrical resistance of the filled skutterudite compound PrOs 4 Sb 12 . The elastic constant C 11 shows a local minimum at around 3 K in 0 T, which shifts to low temperature in 3 T, and seems independent from the heavy fermion superconductivity (HFSC) of the present compound. The temperature and magnetic field dependences of the elastic constant C 11 are consistent with the calculated quadrupole susceptibility based on the crystalline electric field level scheme, indicating well localized 4f -electron states from Pr 3+ at low temperature. The present results strongly suggest that there is no relation between the HFSC and local charge fluctuation, due to off-center quantum tunnneling of the guest Pr 3+ , and also implies that the origin of the heavy fermion state of this compound is not a typical Kondo effect.