Phonon Scattering in Bi₂Te₃/Sb₂Te₃ Superlattice

Ultrafast time-resolved measurements were conducted to investigate scattering mechanism of coherent optical and acoustic phonons in Bi₂Te₃, Sb₂Te₃ and Bi₂Te₃/Sb₂Te₃ superlattice (SL) films. Strong phonon scatterings in the Bi₂Te₃/Sb₂Te₃ SLs are attributed to the interfaces of their hetero-structures. Moreover, decreases of acoustic phonon velocity are observed in SLs, coming from phonon folding and softening. Our results show that both the enhanced interface scattering and the reduced phonon velocity contribute to suppressing the heat transport in SLs.