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

Takeshi Inoshita; Motoaki Hirayama; Noriaki Hamada; Hideo Hosono; Shuichi Murakami

doi:10.1103/PhysRevB.100.121112

paper

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

arXiv:1904.09074 · doi:10.1103/PhysRevB.100.121112

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 ( $≪$ 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.

Revised 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