Fresh from the Oven

Abstract --- The effects of the unique density of states (DOS) of a topological type-II nodal-line semimetal (NLS) on its thermoelectric (TE) transport properties are investigated through a combination of semianalytical and first-principles methods with “spinless Mg₃Bi₂” as the artificial material. The DOS in such a type-II NLS possesses two van Hove singularities near the energy of the nodal line that leads to a large S value compared to the normal metals. Combined with the linear band at the nodal line that gives high electrical conductivity σ, the type-II NLS can exhibit a relatively high TE power factor (PF=S²σ) at the nodal line. In particular, we find PF∼60μW/cmK² at 300 K for the n-type Mg₃Bi₂ by considering the electron-phonon scattering, in which the relaxation time τ of carriers can be expressed as τ∝DOS^-1 for the type-II NLS. Furthermore, we optimize parameters for the TE power factor of type-II NLSs in general by adopting the two-band model with the DOS-dependent relaxation-time approximation. Our results suggest the type-II NLSs as a potential class of high-performance TE materials among metals and semimetals, which are traditionally considered inadequate TE materials compared to semiconductors.