Semimetallic Two-Dimensional Boron Allotrope with Massless Dirac Fermions

It has been widely accepted that planar boron structures, composed of triangular and hexagonal motifs are the most stable two-dimensional (2D) phases and likely precursors for boron nanostructures. Here we predict, based on an ab initio evolutionary structure search, a novel 2D boron structure with nonzero thickness, which is considerably, by $50\text{ }\text{ }\mathrm{meV}/\mathrm{atom}$, lower in energy than the recently proposed $\ensuremath{\alpha}$-sheet structure and its analogues. In particular, this phase is identified for the first time to have a distorted Dirac cone, after graphene and silicene the third elemental material with massless Dirac fermions. The buckling and coupling between the two…

• NS
  National Science Foundation

  Awards: EAR-1114313, DMR-1231586
• UD
  U.S. Department of Energy
• NN
  National Natural Science Foundation of China

  Awards: 91222111, 51332005, 11174152
• DA
  Defense Advanced Research Projects Agency

  Awards: W31P4Q1310005, W31P4Q1210008