Worm-graphene: A two-dimensional orthorhombic carbon semimetal with massless Dirac fermion

Abstract

Low energy Dirac material of carbon other than graphene has always enthralled researchers for their unique properties. Based on first-principles calculation we propose a carbon polymorph identified by the predominance of a Dirac cone in the contiguity of the Fermi level in the Two-dimensional domain. Moreover, the stable pristine structure known as Worm-graphene involves six non-equivalent carbon atoms to effectuate an atomic density 0.372 atoms/Å2 which is close to graphene. The Dirac cone exhibits anisotropic Fermi velocity with 6.85×105 m/s being its highest value. Besides, simple tight-binding Hamiltonian can be formulated to express the origin of the Dirac cone. Interestingly, strain resilient semimetallic behavior with robust Dirac cone of the system can be validated within 10% compressive to 10% tensile strain. Further, the material also possesses anisotropic In-plane Young’s modulus unlike graphene. Appreciable degree of spin-polarization due to monovacancy defect can be established from induced magnetic moment. Additionally, nanotubes rolled-up from this sheet can be both semimetallic or semiconducting depending on the rolling direction. Free standing Worm-graphene sheet shows strikingly different optical response compared to graphene. Two collective oscillations of the system within visible range happen to be the distinguishing trait.