Low-lying excitations at the rare-earth site due to rattling motion in the filled skutterudite LaOs_4Sb_{12} revealed by ^{139}La NMR and ^{121/123}Sb NQR

TL;DR

This study uses NMR and NQR to reveal low-lying excitations at the La site in LaOs4Sb12, attributed to rattling motion, highlighting differences in relaxation behavior between La and Sb sites.

Contribution

It provides experimental evidence of rattling-induced low-lying excitations at the La site in filled skutterudite LaOs4Sb12, using NMR and NQR techniques.

Findings

La site shows a broad maximum in 1/T1T around 50 K.

Additional low-lying excitations are linked to anharmonic phonons.

Sb site relaxation follows the Korringa mechanism.

Abstract

We report experimental results of nuclear magnetic resonance (NMR) at the La site and nuclear quadrupole resonance (NQR) at the Sb site in the filled skutterudite LaOs$_4$Sb$_{12}$. We found that the nuclear spin-lattice relaxation rate divided by temperature $1/T_1T$ at the La site exhibits a different temperature dependence from that at the Sb site. Although $1/T_1T$ at the Sb site is explained by the Korringa mechanism, $1/T_1T$ at the La site exhibits a broad maximum around 50 K, showing the presence of an additional contribution at the La site. The additional low-lying excitations observed at the La site can be understood with the relaxation from anharmonic phonons due to the rattling motion of the La atoms.