(244h) Thermoelectric Transport Coefficients for Weyl Semimetals in the Family of Transition Metal Monopnictides with Dislocation Deffects

Weyl semimetals (WSMs) constitute a remarkable example of three-dimensional, gapless materials with nontrivial topological properties. First proposed theoretically and, more recently, discovered experimentally on TaAs crystals [1] and other transition metal monopnictides. In a WSM, the band structure possesses an even number of Weyl nodes with linear dispersion, where the conduction and valence bands touch. These nodes are monopolar sources of Berry curvature, and hence are protected from being gapped since their charge (chirality) is a topological invariant [2]. In the vicinity of these nodes, conducting states behave as Weyl fermions, i.e., massless quasi-particles with pseudo-relativistic Dirac linear dispersion [2]. In Weyl fermions, conserved chirality determines the projection of spin over their momentum direction, a condition referred to as “spin-momentum locking”.

The presence of Weyl nodes in the bulk electronic spectrum determines the emergence of Fermi arcs [1,2], the chiral anomaly, and the chiral magnetic effect, among other remarkable properties [2]. Therefore, considerable attention has been paid to understand the electronic transport properties of WSMs [2]. Much less explored are the consequences of mechanical strain and defects in WSMs. From a theoretical perspective, it has been proposed that different types of elastic strains can be modeled as gauge fields in WSMs [3-6]. In previous works, we have studied the combined effects of a single torsional dislocation and an external magnetic field on the electronic [4,6] and thermoelectric [3,5] transport properties of WSMs, using the Landauer ballistic formalism in combination with a mathematical analysis for the quantum mechanical scattering cross-sections [3-5].

In this work, we extend our previous analysis to study the case of a diluted, uniform concentration of torsional dislocations and its effects on the electrical conductivity of type I WSMs. In contrast to our former studies [3-5], here we employ the Kubo linear-response formalism at finite temperatures. This requires explicitly calculating the Green´s functions for the system, including the multiple scattering events due to the random distribution of dislocation defects. For this purpose, we first analyze the scattering phase shift arising from a single torsional dislocation, and then we obtain the corresponding (retarded and advanced) Green’s function in terms of the T-matrix elements by solving analytically the Lippmann–Schwinger equation. We further extend this analysis, by incorporating the effect of a random distribution of such dislocations, with a fixed concentration n_d. Finally, we analyze the correction due to the scattering vertex, and by including this additional contribution, we calculate the electrical conductivity, thermal conductivity and Seebeck coefficient from the Kubo formalism, as a function of temperature and concentration of dislocations. We present explicit evaluations of our analytical expressions for the thermoelectric transport coefficients as a function of temperature and concentration of dislocations n_d, for several materials in the family of transition metals monopnictides, i.e., TaAs, TaP, NbAs and NbP, where the corresponding microscopic parameters, estimated by ab initio methods.

References

[1] Xu, S.Y.; et al., Science (2015), 349, 613–617.

[2] Burkov, A., Annu. Rev. Condens. Matter Phys. (2018), 9, 359–378.

[3] Muñoz, E.; Soto-Garrido, R., J. Appl. Phys. (2019), 125, 082507.

[4] Soto-Garrido, R.; Muñoz, E.; Juricic, V., Phys. Rev. Res. (2020), 2, 012043.

[5] Bonilla, D.; Muñoz, E.; Soto-Garrido, R., Nanomaterials (2021), 11, 2972.

[6] Bonilla, D; Muñoz, E., Nanomaterials (2022) 12, 3711.