Strain-induced Weyl and Dirac states and direct-indirect gap transitions in group-V materials

TL;DR

This study uses density-functional theory to explore how strain affects the electronic and mechanical properties of group-V 2D materials, revealing strain-induced topological states and band gap transitions relevant for electronics.

Contribution

It provides comprehensive predictions of strain-induced Weyl and Dirac states, as well as band gap transitions, in group-V materials across various phases, expanding understanding of their tunable properties.

Findings

Predicted strain-induced Dirac states in monolayer As and Sb.

Predicted Weyl states in bulk P and As phases.

Identified numerous band gap transitions under moderate stress.

Abstract

We perform comprehensive density-functional theory calculations on strained two-dimensional phosphorus (P), arsenic (As) and antimony (Sb) in the monolayer, bilayer, and bulk $\alpha$-phase, from which we compute the key mechanical and electronic properties of these materials. Specifically, we compute their electronic band structures, band gaps, and charge-carrier effective masses, and identify the qualitative electronic and structural transitions that may occur. Moreover, we compute the elastic properties such as the Young's modulus $Y$; shear modulus $G$; bulk modulus $\mathcal{B}$; and Poisson ratio $\nu$ and present their isotropic averages of as well as their dependence on the in-plane orientation, for which the relevant expressions are derived. We predict strain-induced Dirac states in the monolayers of As and Sb and the bilayers of P, As, and Sb, as well as the possible existence of Weyl states in the bulk phases of P and As. These phases are predicted to support charge velocities up to $10^6$~$\textrm{ms}^{-1}$ and, in some highly anisotropic cases, permit one-dimensional ballistic conductivity in the puckered direction. We also predict numerous band gap transitions for moderate in-plane stresses. Our results contribute to the mounting evidence for the utility of these materials, made possible by their broad range in tuneable properties, and facilitate the directed exploration of their potential application in next-generation electronics.