ONE-DIMENSIONAL TOPOLOGICAL ELEMENTS IN NOVEL MATERIALS

Topological metals and semimetals have become a new focus in research after the development of TIs owing to their possible application in future electronic and spintronic devices. Nodal-point, -line, and -surface semimetals are three typical TSMs. The first one has zero-dimensional (0D) topological elements (TEs), which are generated by crossing points in the momentum spaces. The second one has a one- dimensional (1D) TE, which is generated by band crossing along a line. The final one has a two-dimensional (2D) TE, which is formed by the conduction and valence band crossing points on closed nodal surfaces in the Brillouin zone (BZ). Nodal line semimetals were initially proposed in some carbon-based networks and have received intense attentions because of their unique electronic and optical properties and nontrivial drumhead-like surface states. In addition, the conjunction among multiple nodal lines can induce new band topology.