A novel two-dimensional all-carbon Dirac node-line semimetal

Carbon allotropes have vast potential in various applications, including superconductivity, energy storage, catalysis, and photoelectric semiconductor devices. Recently, there has been significant research interest in exploring new carbon materials that exhibit unique electronic structures. Here, we propose a novel two-dimensional (2D) carbon allotrope called TCH-SSH-2D, which possesses a Dirac node-line (DNL) semimetallic state. The structure of TCH-SSH-2D is derived from the TCH-type Archimedean polyhedral carbon cluster units, combined with the SSH lattice model, possessing a space group of tetragonal P4/mmm. Using first-principles calculations, we demonstrate that the system is dynamically, thermodynamically, and mechanically stable. It exhibits an energetically favorable structure with no imaginary frequency in the phonon dispersion curves and elastic constants satisfying the Born-Huang stability criterion. Our findings not only contribute to a deeper understanding of the carbon allotrope family but also provide an opportunity to explore unique Dirac states in two-dimensional pure carbon systems.