New Recipe for Enhancing the Thermoelectric Performance in Topological Materials Carrying Single-Pair Weyl Points Fermions and Phonons

The emergence of various topological semimetal states presents a novel opportunity for enhancing the efficiency of thermoelectric transport. This study introduces a recipe to improve the thermoelectric (TE) performance in topological materials containing single-pair Weyl points (SP WPs) fermions and phonons. The recipe focuses on two key factors contributing to the enhancement of TE performance: the increase in the density of states to achieve a high power factor, and the introduction of additional phonon scattering to reduce the lattice thermal conductivity. The proposed recipe is confirmed in a half-metallic SP WPs material BaNiIO6 through first-principles methods. An enhanced density of states arises near the energy of the SP WPs in BaNiIO6, leading to a peak power factor connected to the complex Fermi surface due to the degeneracy of Weyl pockets in energy. Furthermore, it is shown that the SP WPs phonons in BaNiIO6 possess a high scattering rate and can likely contribute to the low lattice thermal conductivity, especially when two crossing points in SP WPs do not degenerate in frequency. The new recipe can be used for discovering high-performance thermoelectric materials in the future by utilizing the transport advantages of degenerate-in-energy SP WPs fermions and non-degenerate-in-frequency SP WPs phonons.