A New Anisotropic Dirac Cone Material: A B₂S Honeycomb Monolayer

Abstract

Different from the isotropic Dirac cones existing in other two-dimensional (2D) materials, anisotropic Dirac cones have the merit of anisotropic carrier mobility for applications in direction-dependent quantum devices. Motivated by the recent experimental finding of an anisotropic Dirac cone in borophene, here we report a new 2D anisotropic Dirac cone material, BS monolayer, identified by using a global structure search method and first-principles calculation combined with a tight-binding model. The BS monolayer is found to be stable mechanically, thermally, and dynamically and exhibits an anisotropic Dirac cone exactly at the Fermi level, showing a Fermi velocity of 10 m/s in the same order of magnitude as that of graphene. Moreover, BS monolayer is the first anisotropy Dirac cone material with a pristine honeycomb structure stabilized by S in free-standing conditions where each atom has four valence electrons on average being isoelectronic to C. This study would expand the Dirac cone material family with new features.

Tuning the electronic structure and magnetic coupling in armchair B2S nanoribbons using strain and staggered sublattice potential

“…As very recently reported [4], the most energetically stable structure of B 2 S monolayer predicted by using global structure search method and first principles calculation combined with tight-binding model, is shown in Fig.1 from which we can see that the planar 2D structure consists of honeycomb lattices, similar to graphene. This honeycomb structure is a global minimum in the space of all possible 2D arrangements of B 2 S in which each hexagonal ring is distorted with the bond angles ranging from 114Å to 123Å, because B and S atoms have different covalent radii and electronegativities [4,5].…”

“…The geometrical structure of the pristine armchair edge B 2 S nanoribbon, lying in the xy plane, is depicted in Fig.1 (d). As shown in this figure, each hexagon consists of four B atoms and two S atoms, with an orthogonal primitive cell with a space group of P BAM and a point group D 2 h. As shown in Fig.1, the bonding length between two adjacent B atoms (B-B bonds) was calculated to be 1.62Å, from the relaxed structure whereas the distances between B and S atoms (B-S bonds), are all of the same length 1.82Å [4]. The black balls correspond to the boron atoms (B) and the white ones correspond to the sulfur atom (S).…”

Strain-induced modulation of exchange interaction in monolayer zigzag nanoribbons of B2S

“…The geometry structure of a monolayer zigzag nanoribbon of B 2 S, laid in the xy plane, is depicted in Fig.1. As shown in this figure, each hexagon consists of four B atoms and two S atoms, with an orthogonal primitive cell with a space group of P BAM and a point group D 2 h. In this structure, there are two kinds of bonds with 1.62Åand 1.82Åbond lengths for B-B and B-S connections, respectively [38].…”

“…To verify the role of strain in the magnetic exchange interaction, the understanding of changes in the band structure and bandgap transformation is crucial. For B 2 S monolayer, it is shown that the bands near the Fermi level are originated from the p z orbitals [38]. A nearest-neighbor effective tight-binding Hamiltonian, in the basis of p z orbitals and in the second quantized representation has recently been modeled [38] and is given by…”

“…On the other hand, strain engineering, a key strategy for manipulating the magnetic coupling in 2D nanostructures [30], has a perfect platform for its implementation in the atomically thin materials. Motivated by the search for materials for spintronics, a huge number of works have been performed to examine the effectiveness of mechanical strain in modulating the magnetic properties of 2D layered materials [30][31][32][33][34][35][36][37] Very recently, a new 2D anisotropic Dirac cone material, B 2 S monolayer, appears in the research field again, by using global structure search method and first principles calculation combined with tight-binding model [38,39]. B 2 S monolayer, showing a Fermi-velocity of 106 m/s in the same order of magnitude as that of graphene, was found to be mechanically, thermally and dynamically stable.…”