Superconductivity in topological Ψ-graphene

Typical Dirac cones in graphene induce the absence of electronic density around the Fermi energy level (E_f), prohibiting intrinsic superconductivity. Here, we tested the theoretical superconducting properties of graphene after introducing pentagonal and heptagonal carbon rings into the structure. Generally, 5-7 polygons of a metastable Ψ-graphene monolayer break the hexagonal symmetry to form type-II Dirac cones by band crossings. The polyhedral structure maintains integrity under high temperatures. The large specific surface area of the Ψ-graphene monolayer facilitates the physical adsorption of NO molecules. Weak interactions of atomic bonding and antibonding features coexist with the Bader charge transfer in the carbon monolayer in close proximities to one another. The collective vibrations of carbon, nitrogen, and oxygen atoms provide good dynamic stability of the Ψ-graphene-NO adsorption system. In the Ψ-graphene monolayer, the shift of Dirac cones leads to the formation of visible Fermi surfaces, which motivates further investigation into their influences on the superconducting properties. Out-of-plane and in-plane carbon vibrations are attributed to phonon modes in mediation with electron couplings. After computing the Eliashberg function, we evaluated strong electron-phonon coupling, with the superconducting transition temperature reaching 22 K. These theoretical predictions can stimulate interests in exploring topological graphene allotropes of intrinsic superconductivity.