Orbital Chern insulators in Honeycomb Pnictogen Monolayers

The Orbital Hall Effect is characterized by the transport of electrons through the orbital angular momentum degree of freedom. The orbital Hall insulating state can be viewed as a novel topological state that arises from an orbital Chern insulator. Here, we discuss the orbital Chern insulators in the honeycomb pnictogen monolayers, such as blue-phosphorene, arsenene, and β-antimonene, by defining the orbital Chern number (C_L) via the feature-spectrum topology approach [1]. Note that the orbital Chern insulator state in pnictogen honeycomb monolayers is generally not driven by spin-orbit coupling. We find C_L= 2 in the honeycomb pnictogen monolayer family, which signifies the presence of non-trivial L_z-feature edge states that connect distinct L_z sectors. Furthermore, the orbital Chern number is equal to the number of non-trivial edge states [2]. These edge states are situated within the bulk energy gap, isolated from both the valence and conduction bands. Our study opens a new pathway for exploring topological materials categorized by the orbital angular momentum.