First-principles calculations of transport coefficients in the Weyl semimetal TaAs

Abstract

We study charge and heat transport from first principles in the topological Weyl semimetal TaAs. Electronphonon coupling matrix elements are calculated using density-functional perturbation theory and used to derive the thermoelectric 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 that they give similar results for TaAs provided the chemical potential is treated accurately. We derive a second equation in the iterative method to solve for transport under thermal gradients. Interestingly, the Onsager reciprocity between S and ∏ longer imposed, allowing us to treat systems that break time-reversal symmetry, in particular, magnetic materials. We compare our results with available experimental data for TaAs: the agreement is excellent for σ<subv>xx, while σzz is overestimated, probably caused by differences in experimental carrier concentrations. The Seebeck coefficient is of the same order of magnitude in theory and in experiments, and we find that its low-T behavior also strongly depends on the doping level.