  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 ab
initio evolutionary structure search, novel 2D boron structure with non-zero
thickness, which is considerably, by 50 meV/atom lower in energy than the
recently proposed 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 sublattices not only
enhance the energetic stability, but also are the key factors for the emergence
of the distorted Dirac cone.

Materials Science