Theoretical realization of two-dimensional Dirac/Weyl line-node and traversing edge states in penta-X2Y monolayers

Abstract Recently, two-dimensional (2D) materials with pentagonal (penta-) structure have attracted broad attention because of their interesting structure and associated novel mechanical, optical, electronic and magnetic characteristics. Here, from first-principles, we propose a series of penta-materials with X2Y configuration remarkably show nontrivial line-node band structures. The line-nodes are either Dirac-like or Weyl-like, depending on the variety of band-degeneracies induced by intrinsic magnetism. Interestingly, the Dirac/Weyl line-nodes in penta-X2Y are open loops traversing the entire 2D Brillouin zone, which are different with the closed loops in previous 2D line-node examples. We further find the open 2D line-nodes are characterized with long edge states which can penetrate the whole boundary. The open Dirac/Weyl line-nodes and the traversing edge states proposed here are favorable candidates to study nontrivial topology and promote potential applications in nanoscale electronics and spintronics systems.