Palgraphyne: A Promising 2D Carbon Dirac Semimetal with Strong Mechanical and Electronic Anisotropy

For next‐generation carbon‐based nanoelectronics, it is highly desirable to search for easily obtained 2D carbon allotropes with various appealing properties. Herein, based on first‐principles calculations, a new 2D carbon Dirac semimetal with orthorhombic symmetry is identified, which is composed of a carbon skeleton of para‐xylene and acetylenic linkages, and is thus termed palgraphyne [pæl'græfain]. The calculations of stability reveal not only that palgraphyne is dynamically, thermally (above 1000 K), and mechanically stable, but also that it is energetically more preferable to the recently synthesized β‐graphdiyne and γ‐graphdiyne. Due to the particular atomic‐framework, the calculations of Young's modulus and Poisson's ratio show that palgraphyne is mechanically anisotropic with a sizable ratio between the maximum and minimum value up to 3.29. Remarkably, unlike the case of graphene, the Dirac cones of palgraphyne are distorted. As a result, its electronic transport properties also exhibit anisotropy, with different Fermi velocities along diverse orientations. The highest Fermi velocity reaches up to 8.89 × 105 m s−1 in the kx + ky direction, which is very close to that of prominent graphene (9.0 × 105 m s−1). The findings highlight a distinct 2D anisotropic Dirac semimetal, which has great potential applications in nanodevices. Palgraphyne [pæl'græfain] composed of a carbon skeleton of para‐xylene and acetylenic linkages is identified as a new stable 2D carbon Dirac semimetal. First‐principles calculations demonstrate that palgraphyne holds mechanical anisotropy with a sizable ratio up to 3.29 and electronic anisotropy with direction‐dependent Fermi velocities in which the highest value reaches up to 8.89 × 105 m s−1.