Design and modulation of two-dimensional Dirac materials in beryllium/boron-based binary monolayers

In the periodic table, beryllium (Be) and boron (B) as typical light element are near neighbors of carbon (C). Survey the electron-deficiency in Be and B as compared with C, if introducing external electrons in principle can offset the electron-deficiency, it seems that a Dirac cone have a possibility to exist in Be/B-based structures, like as C-structure (e.g., graphene). Motivated by this inference, here we selected elements P/Se as electron-rich donors to make up special Be/B-based binary compositions (BeP₂/B₂Se) being isoelectronic with graphene. Using a global structure search method combined with first-principles calculation, we identified three stable two-dimensional (2D) monolayers, namely o-BeP₂, α-B₂Se and β-B₂Se. As expected, these three monolayers are verified to possess intrinsic or strain-inducing Dirac cone. When applied with a 6% compressive strain, the o-BeP₂ even can be converted to Dirac cone material. The two low-lying B₂Se monolayers (α-B₂Se and β-B₂Se) possess a hexagonal honeycomb lattice, showing a natural Dirac cone and their Fermi velocities are in the same order of that of graphene. These configurations can be further expanded to the isoelectronic BeAs₂ and B₂S stoichiometries and a Dirac cone can be found. This isoelectronic strategy offers a possible route to design the 2D Dirac material in Be/B-based binary compounds.