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

Abstract

This work establishes the existence of dispersive nodal-arcs and their evolution into Weyl nodes under the effect of spin-orbit coupling (SOC) in NbAs and NbP. The obtained features mimic the observations as reported for TaAs and TaP in our previous work (Pandey in J Phys Condens Matter 35:455501, 2023). In addition, this work reports that the number of nodes in the TaAs class of Weyl semimetals (WSMs) can be altered by creating strain along a or c direction of the crystals. 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. In the absence of SOC, a 3% tensile (compressive) strain along the a (c) direction leads to the partially merging of nodal-lines in the extended BZ of NbAs and NbP, which is not observed in TaAs and 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. Next, 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. Weyl-cone contributed S in these WSMs is found to be anisotropic within the temperature range of 0–100 K. The value of S contributed from Weyl cone is found to be as large as \(\sim \)70 \(\mu \)V/K below 25 K in case of NbP. Lastly, the expected effect of axial strain and change in SOC-strength on S of TaAs class of WSMs is discussed. 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.