Coexistence of topological nodal lines, Weyl points, and triply degenerate points in TaS

We theoretically propose that, the single crystal formed TaS is a new type of\ntopological semimetal, hosting ring-shaped gapless nodal lines and triply\ndegenerate points (TDPs) in the absence of spin-orbit coupling (SOC). In the\npresence of SOC, the each TDP splits into four TDPs along the high symmetric\nline in the momentum space, and one of the nodal ring remains closed due to the\nprotection of the mirror reflection symmetry, while another nodal ring is fully\ngapped and transforms into six pairs ofWeyl points (WPs) carrying opposite\nchirality. The electronic structures of the projected surfaces are also\ndiscussed, the unique Fermi arcs are observed and the chirality remains or\nvanishes depending on the projection directions. On the (010) projected\nsurface, one may observe a Lifshitz transition. The new type of topological\nsemimetal TaS is stable and experimentally achievable, and the coexistence of\ntopological nodal lines, WPs and TDPs states in TaS makes it a potential\ncandidate to study the interplay between different types of topological\nfermions.\n