Orthorhombic C32: A topological semimetal with nodal ring

Abstract

We identify by ab initio calculations a new topological semimetal with a nodal ring in an sp2-sp3 hybridized carbon network, with a 32-atom base-centered orthorhombic unit cell in Cccm (D2h20) symmetry, termed as bco-C32 carbon. The dynamical stability of bco-C32 carbon has been confirmed with phonon mode calculations and the thermal stability has been confirmed by molecular dynamics simulations. Electronic band structures calculations show that bco-C32 carbon is a topological nodal line semimetal with a closed nodal ring centering the high-symmetric Γ point inside the first Brillouin zone, and the drumhead-like topological non-trivial surface states can be seen inside or outside the projected nodal ring in the (001) surface depending on the different surface terminations. Moreover, the calculated optical properties show that bco-C32 carbon is a dark black carbon phase like as graphite. Our findings have identified a new sp2-sp3 hybridized carbon allotrope and provide insights for its physical properties.