Insights into the lattice thermal conductivity of solids carrying type-I and type-II Weyl point phonons

In recent years, utilizing the exotic electrical/thermal transport properties of topological quantum states of matter has been proven as a new route to improve the performance of thermoelectric generators. However, previous achievements made by this recipe are mainly focused on topological insulators or semimetals, the physical consequences between topological phonons and lattice thermal conductivity still remain largely unexplored. Here, taking CdTe and SrSi2 solids as examples, respective presence of type-II and type-I Weyl point phonons, we systematically investigate their thermal transport properties by density functional theory and Boltzmann transport equation. Our calculations show that type-II Weyl point phonons in CdTe exhibit a vanishing contribution to lattice thermal conductivity due to the small group velocity and high three-phonon scattering phase space. In contrast to three-phonon, four-phonon scattering is less readily allowed and shows a marked scattering dip around the Weyl point. Nevertheless, four-phonon scattering plays a significant role in CdTe, which diminishes the lattice thermal conductivity from 9.85 to 1.64 W m−1K−1 at 300 K, by almost 83%. Type-I Weyl point phonons in SrSi2 exhibit normal behavior that does non-negligible contribution to lattice thermal conductivity among the optical frequency region. This is primarily ascribed to the overshadowed three-phonon scattering for type-I dispersion of Weyl nodes. However, four-phonon scattering appears to remain robust against type-I dispersion in contrast to the marked scattering dip of type-II dispersion in CdTe. Overall, four-phonon scattering is weaker in SrSi2 as compared to CdTe, which lowers the lattice thermal conductivity from 2.62 to 2.21 W m−1K−1, by only 15%. This work provides a thorough understanding of the intrinsic relationship between Weyl point phonons and thermal transport and helps to uncover unusual thermal-related performance of Weyl systems.