Dirac loops in two-dimensional topological material T-graphene

Graphene possesses a peculiar band structure and hence exhibits many fascinating properties from room temperature quantum Hall effect to massless Dirac fermions. With the understanding of graphene, topological materials with the properties similar to or even beyond graphene gradually rise and draw much attention, such as Silicene, Bi2Se3, WTe2 and most recently TaAs. Then a question arises: is it possible for another 2D carbon lattice to exhibit similar properties? If so, what are the determining factors? Here, we demonstrate that a novel two-dimensional carbon allotrope called T-graphene can possess Type-I Dirac points / loops based on the first-principles calculations [1]. T-graphene described by the plane group p4mm (See Fig. 1) can be energetically metastable and dynamically stable. The band structure of T-graphene in Fig. 1 shows the linear dispersion relation at the Fermi level. Two Dirac points are located at asymmetric positions Ξ(0.170, 0.170) between Γ and M and Λ(0, 0.249) between X and Γ, respectively. Furthermore, the linear dispersion relation near the Fermi surface exists in every direction and the cross points form a loop. Such Dirac fermions and a high υF are attributed to crossing π and π* bands and two sublattices. Under certain structure tailoring or straining, the linear dispersion relation is found to be retained. Two type of nanoribbons tailored from T graphene are predicted to have interesting magnetic properties. Besides, two possible routes to obtain T graphene are proposed: carbon deposition on certain metal substrates or electron beam irradiation on the tailored graphene growing on Ni (111). The results provide new insights to search and fabricate two-dimensional topological material.