Topologically protected states and half-metal behaviors: Defect-strain synergy effects in two-dimensional antimonene

Abstract

Two-dimensional (2D) materials often feature defects and strain, due to their atomic layered character, which can cause problems for applications. Antimonene, a monolayer material derived from layered bulk Sb, undergoes a semiconductor-to-topological-insulator transition under large strain. However, it is unclear whether the structure and properties of antimonene are retained under strain once defects are generated. Here, we used ab initio calculations to explore a series of the most probable defects in these materials, including the Stone-Wales (SW) defects, single vacancies, double vacancies (DV), and adatoms. Interestingly, the influence of defects can be categorized into two types: for defects involving the loss/addition of an odd number of atoms, the material becomes ferromagnetic and exhibits half-metal properties under a certain strain; for defects involving an even number of missing atoms, the material remains a nonmagnetic semiconductor. Moreover, the topological phase transitions are robust for Sb monolayers with SW defects, but the critical transition strain decreases. Conversely, topological phase transitions might vanish for DV (555|777) and DV (5|8|5) defects. Our calculations suggest that different types of defects and strain might transform antimonene into a semiconductor, half-metal, or topological insulator. Therefore, defects and strain effects in antimonene should be carefully controlled for its applications.