Semimetallic Two-Dimensional Boron Allotrope with Massless Dirac Fermions

TL;DR

This paper predicts a new stable 2D boron structure with non-zero thickness that hosts massless Dirac fermions, expanding the understanding of boron nanostructures and their electronic properties.

Contribution

It introduces a novel 2D boron allotrope with a distorted Dirac cone, which is more stable than previous structures and exhibits unique electronic features.

Findings

New 2D boron structure with non-zero thickness identified.

Structure exhibits a distorted Dirac cone with massless fermions.

Enhanced stability due to buckling and sublattice coupling.

Abstract

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.