Thermoelectric transport in Weyl semiconductor tellurium: The role of Weyl fermions

Abstract

Connecting topological quantum states and thermoelectric transport offers new promise in improving the thermoelectric performance, narrow band gap semiconductor hosting Dirac/Weyl points (DPs/WPs) around the Fermi level are promising candidates for this prospect. In this work, we investigate the thermoelectric properties of Weyl semiconductor tellurium using density functional theory combined with Boltzmann transport theory. An indirect band gap without spin orbital coupling (SOC) is 0.31 eV, while it shifts down to a direct 0.14 eV after involving SOC. Due to the lack of space inversion symmetry in tellurium, spin orbital coupling (SOC) enables band splitting and crossing, resulting in the formation of WPs. We find that the existence of WP fermions should be a likely contributor to higher Seebeck coefficient. The peak p-type S²σ/τ under SOC arises near the WP in cooperation with the extrema of the lower valence band. The p-type zT_e under SOC is higher than that without SOC within the energy section where the WPs exist. When breaking the WPs in a reformed tellurium, the p-type thermoelectric coefficients exhibit slight decrease, which in turn indicates the benefit of WP fermions in thermoelectric performance. Our calculations help to understand the role of WP fermions in thermoelectric transport properties.