Collective-Goldstone-mode-induced ultralow lattice thermal conductivity in Sn-filled skutterudite SnFe_4Sb_(12)

摘要

We demonstrate that the concept of Goldstone bosons can be exploited for phonon control and thermal conductivity reduction of materials. By studying lattice dynamics of the Sn filled skutterudite SnFe_4Sb_(12), we find Sn off-centers in its coordination cage in contrast to the common rare earth fillers. This leads to low-frequency Goldstone-like modes below 1 THz associated mainly with Sn motions. Importantly, these involve collective motion of other atoms, especially Sb, in the host skutterudite lattice. The optical modes trans versing to the Sn off-centering direction are identified as Goldstone type modes in association with a three-dimensional Mexican-hat-like potential energy surface. The interaction of these collective Goldstone modes with the host heat-carrying phonons is shown to lead to ultralow lattice thermal conductivity.