Topological semimetal phases manifested in transition metal dichalcogenides intercalated with 3d metals

Abstract

In the search for stable topological semimetals with clean band profiles, we have screened all the 3$d$ metal-intercalated transition-metal dichalcogenides (3dI-TMDCs) by performing hybrid-functional-based ab initio calculations. Two classes of topological materials featuring twelve Weyl nodes in the $k_z=0$ plane (without spin-orbit interactions) are identified: (a) time-reversal-breaking Weyl semimetals VT${}_3$X${}_6$ (ferromagnetic) and (b) spinless Weyl semimetals MnT${}_3$X${}_6$ (nonmagnetic), where T=Nb, Ta; X=S, Se. VNb${}_3$S${}_6$, prototypical of class (a), is half-metallic with only two bands crossing at the Fermi level to form Weyl nodes. MnNb${}_3$S${}_6$ in the nonmagnetic phase is essentially a spinless version of VNb${}_3$S${}_6$ featuring an equally clean and simple band profile. Although the space group symmetry (P6${}_3$22) implies that the degeneracy between the two bands is lifted for $k$ away from the Weyl nodes, the gap remains extremely small ($\ll$ 0.1 meV) along a loop connecting the Weyl nodes. This quasi-nodal-line degeneracy is explained in terms of the quasi-mirror symmetry of the lattice, induced by the in-plane twofold rotation axes, and the specific orbital nature of the bands. 3dI-TMDCs are chemically and thermally stable stoichiometric compounds containing no toxic elements and are a viable platform for the study of topological condensed-matter physics.

arXiv commentRevised to include a detailed discussion of the effect of spin-orbit interactions on the topology of VNb${}_3$S${}_6$. [See Figs. 2(d) and (e).] The other figures were also updated for enhanced clarity

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