In the last few decades, the study of topological materials has been carried out on an extensive scale. Half-Heusler alloys are well known for their topological behaviours. In this work, we present a detailed study of topological properties of a ternary half-Heusler alloy, YAuPb, using the tight-binding approach. We have calculated some important topological properties which includes-finding nodes and their chiralities, Berry curvature (Ω) and the surface-states. Five pairs of characteristic nodes with equal and opposite chiralities are obtained. Based on the study of these properties, we categorise the material as non-trivial topological semimetal. Besides the topological behaviours, we present a comparative study of temperature dependent transport properties corresponding to the chemical potential (μ) of the Fermi level and the node points. The temperature range chosen for the study is 50-300 K. The results obtained from the calculations of electrical conductivity per unit relaxation time (σ/τ ) and the electronic part of thermal conductivity per unit relaxation time (κ 0 ) indicates the conducting nature of the material to both the heat and electricity. At the Fermi level, the value of Seebeck coefficient (S) is found to be ∼ −9.07 (−35.95) μV K −1 at 50(300) K. The negative value of S indicates the n-type behaviour of the compound. The calculated value of electronic specific heat (Pauli magnetic susceptibility) corresponding to Fermi level is ∼ 0.03(0.18) × 10 −2 J mol −1 K −1 (∼ 1.21(1.14) × 10 −10 m 3 mol −1 ) at 50(300) K. This work suggests that YAuPb is a promising candidate of non-trivial topological semimetals which can be employed in transmission of heat and electricity, and as n-type material within the temperature range of 50-300 K.
In this work, we report the existence of nodal-arc, which acts as the building block of all the nodal-rings in TaAs & TaP. This nodal-arc is found to be capable of generating all the nodal-rings in these materials upon the application of space-group symmetry operations including time-reversal symmetry. The arcs are obtained to be dispersive with the energy spread of ∼109 (∼204) meV in TaAs (TaP). Also, the orbitals leading to bands-inversion and thus the formation of nodal-arcs are found to be Ta-5d & As-4p (P-3p) in TaAs (TaP). The area of nodal-rings is found to be highly sensitive to the change in hybridization-strength, where the increase in hybridization-strength leads to the decrease in the area of nodal-rings. In the presence of spin-orbit coupling (SOC), all the points on these arcs get gaped-up and two pairs of Weyl-nodes are found to evolve from them. Out of the two pair, one is found to be situated close to the joining point of the two arcs forming a ring. This causes the evolution of each nodal-ring into three pairs of Weyl-nodes. The coordinates of these Weyl-nodes are found to be robust to the increase in SOC-strength from ∼ 0.7-3.5 eV. All the results are obtained at the first-principle level. This work provides a clear picture of the existence of nodal-arc due to accidental degeneracy and its evolution into Weyl-nodes under the effect of SOC.
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