Orbital Chern insulators in Honeycomb Pnictogen Monolayers

Yueh-Ting Yao^1*, Arun Bansil², Hsin Lin³, Tay-Rong Chang^1,4,5

¹Department of Physics, National Cheng Kung University, Tainan, Taiwan
²Department of Physics, Northeastern University, Boston, Massachusetts, USA
³Institute of Physics, Academia Sinica, Taipei, Taiwan
⁴Center for Quantum Frontiers of Research and Technology (QFort), Tainan, Taiwan
⁵Physics Division, National Center for Theoretical Sciences, Taipei, Taiwan

* Presenter:Yueh-Ting Yao, email:ytyao1001@gmail.com

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 (CL) 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 CL=2 in the honeycomb pnictogen monolayer family, which signifies the presence of non-trivial Lz-feature edge states that connect distinct Lz 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 valance and conduction bands. Our study opens a new pathway for exploring topological materials categorized by the orbital angular momentum.

[1] B. Wang, Y.-C. Hung, X. Zhou, T. Ong, and H. Lin, Feature spectrum topology. arXiv:2310.14832 (2022)
[2] Yueh-Ting Yao et al., Feature-energy duality of topological boundary states in a multilayer quantum spin Hall insulator. Phys. Rev. B 109, 155143 (2024)

Keywords: Topological Material, Orbital Chern Insulator, Honeycomb Pnictogen Monolayer