  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.
