An ab-initio study of nodal-arcs, axial strain's effect on nodal-lines & Weyl nodes and Weyl-contributed Seebeck coefficient in TaAs class of Weyl semimetals

Abstract

This work verifies the existence of dispersive \textit{nodal-arcs} and their evolution into Weyl nodes under the effect of spin-orbit coupling (SOC) in NbAs & NbP. The obtained features mimic the observations as reported for TaAs & TaP in our previous work. In addition, this work reports that the number of nodes in TaAs class of Weyl semimetals (WSMs) can be altered via creating strain along $a$ or $c$ direction of the crystal. For instance, the number of nodes in NbAs under SOC-effect along with 2% (3%) tensile-strain in $a$ direction is found to be 40 (56) in its full Brillouin zone (BZ). Besides the nodes, such strain are found to have considerable impact on the nodal-lines of these WSMs when effect of SOC is ignored. A 3\% tensile (compressive) strain along the $a$ ($c$) direction leads to the partially merging of nodal-lines (without SOC) in the extended BZ of NbAs \& NbP, which is not observed in TaAs & TaP within the range of -3% to 3% strain. Apart from this, the work discusses the role of Weyl physics in affecting the Seebeck coefficient ($S$) of any WSM. In this direction, it is discussed that how a symmetric Weyl cone, even if tilted, will have no contribution to the $S$ of WSMs. Furthermore, the work highlights the conditions under which a Weyl cone can contribute to the $S$ of a given WSM. Lastly, the discussion of Weyl contribution to $S$ is validated over TaAs class of WSMs via investigating the features of their Weyl cones and calculating the contributions of such cones to the $S$ of these semimetals. The value of $S$ contributed from Weyl cone is found to be as large as $\sim$65 $\mu$\textit{V}/\textit{K} below 25 K in case of TaAs. The findings of this work present a possibility of engineering the topological properties of TaAs class of WSMs via creating strain in their crystal. It also makes the picture of Weyl physics impact on the $S$ of WSMs a more clear.