Electronic and optical properties of non-hexagonal Dirac material S-graphene sheet and nanoribbons

In this paper, we have critically explored the electronic, magnetic and optical properties of stable non-hexagonal carbon allotrope S-graphene (SG). The band structure of SG sheet exhibits two Dirac cones at distinct (k) over right arrow points. The ab-initio molecular dynamics study reveals the dynamical stability of the system up to 600 K. Besides, the sheet possesses appreciable mechanical stability. Furthermore, the electronic properties of the ribbons strongly depend on the edge geometry and width. The A-type S-graphene nanoribbons (SGNRs) with even N exhibit width-dependent direct bandgap semiconducting nature. Whereas, A-SGNRs with odd N are semi-metallic. In contrary, B-SGNRs are uniformly semi-metallic except for extremely narrow N = 1 and 2 case. Besides, the unexpected occurrence of Dirac point for the N = 4.5 C-SGNR has been explored. Moreover, the optical response of the sheet and nanoribbons are highly anisotropic. We have critically obtained the plasma frequency for the collective electron oscillation of the sheet at 5.37 eV under parallel incidence of electromagnetic waves. Besides, the effective number of electrons participating in direct interband transitions in sheet show a quasi-saturation between 3-10 eV. We thus expect these theoretical predictions will provide a basic understanding of the opto-electronic responses towards possible application of this non-hexagonal graphene network with multiple Dirac cones.