First-principles calculations of transport coefficients in Weyl semimetal TaAs

TL;DR

This paper uses first-principles calculations to analyze charge and heat transport in the Weyl semimetal TaAs, providing detailed insights into its thermoelectric properties and comparing theoretical results with experimental data.

Contribution

It introduces a comprehensive first-principles approach to calculate transport coefficients in Weyl semimetals, including the derivation of an additional equation for coupled thermal and electrical transport.

Findings

Excellent agreement with experimental electrical conductivity in the xx direction

Overestimation of conductivity in the zz direction possibly due to carrier concentration differences

Seebeck coefficient predictions align with experimental magnitude and doping dependence

Abstract

We study charge and heat transport from first-principles in the topological Weyl semimetal TaAs. Electron-phonon coupling matrix elements are calculated using density functional perturbation theory and used to derive the thermo-electric transport coefficients, including the electrical conductivity, Seebeck coefficient, electronic thermal conductivity and the Peltier coefficient. We compare the self-energy and momentum relaxation time approximations to the iterative solution of the Boltzmann Transport Equation, finding they give similar results for TaAs provided the chemical potential is treated accurately. For the iterative method, we derive an additional equation, which is needed to fully solve for transport under both thermal and an electrical potential gradients. Interestingly, the Onsager reciprocity between $S$ and $\Pi$ is no longer imposed, and we can deal with systems breaking time-reversal symmetry, in particular magnetic materials. We compare our results with the available experimental data for TaAs: the agreement is excellent for $\sigma_{xx}$, while $\sigma_{zz}$ is overestimated, probably due to differences in experimental carrier concentrations. The Seebeck coefficient is of the same order of magnitude in theory and experiments, and we find that its low-T behavior also strongly depends on the doping level.