Rectangular Carbon Nitrides C₄N Monolayers with a Zigzag Buckled Structure: Quasi‐1D Dirac Nodal Lines and Weak Topological Properties with Flat Edge States

Abstract

Using first‐principles calculations, two C4N monolayers with a zigzag buckled (ZB) structure are proposed. The ZB C4N monolayers contain raised‐C (raised‐N) atoms with sp3 hybridization, different from the traditional 2D graphene‐like carbon nitride materials with sp2 hybridization. Interestingly, the band structures of the ZB C4N monolayers exhibit quasi‐1D Dirac nodal line resulting from the corresponding quasi‐1D structure of the zigzag carbon chains, which is essentially different from the conventional ring‐shaped nodal line. The quasi‐1D Dirac nodal line exhibits the following features: i) gapless Dirac points, ii) varying Fermi velocity, and iii) a slightly curved band along the high‐symmetry path. All these features are successfully explained by the proposed tight‐binding model that includes interactions up to the third nearest neighbor. The Fermi velocity of the 2D system can reach 105 m s−1, which is promising for applications in high‐speed electronic devices. The topological flat band structure of the corresponding 1D system determined by the Zak phase and band inversion is edge‐dependent, which is a weak topological state and can be explained by the 2D Su‐Schrieffer‐Heeger (SSH) model. The quasi‐1D Dirac Fermions and SSH edge states make the ZB C4N monolayers promising for nanoelectronics applications.