Intersecting nodal rings in orthorhombic-type BaLi2Sn compound

Abstract

Topological semimetals, such as topological nodal point semimetals (TNPSs) and topological nodal line state semimetals (TNLSs), featuring zero-dimensional (0D) and one-dimensional (1D) topological elements (TEs), respectively, have attracted widespread attention in recent years. In this study, via first-principles, we predict that a recently synthesized BaLi₂Sn material with Pmmn structure is a TNLS with perfect intersecting nodal rings in the k_x = 0 and k_y = 0 planes when the spin–orbit coupling (SOC) effect is ignored. The intersecting nodal rings were further checked by employing a low-energy effective Hamiltonian near the Γ point. Surface drum-head-like state was observed, which further confirms the 1D TE in this system. When the SOC is included, although the SOC-induced gaps opened in the band crossing points, a Dirac cross-like surface state was observed for this system. It should be noted that this material was thermally and mechanically stable, and it is hoped that the 1D TE and interesting surface states can be experimentally demonstrated soon.