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Enhanced Thermoelectric Performance by van Hove Singularities in the Density of States of Type-II Nodal-line Semimetals
N. H. Tung, J. M. Adhidewata, A. R. T. Nugraha, and R. Saito
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.
Phys. Rev. B 105, 115142 (2022) Back to Publications