Two-dimensional Topological Crystalline Insulator Phase in Sb/Bi Planar Honeycomb with Tunable Dirac Gap
Chia-Hsiu Hsu1, Zhi-Quan Huang1*, Christian P. Crisostomo1, Liang-Zi Yao1, Feng-Chuan Chuang1, Yu-Tzu Liu2,3, Baokai Wang2,3,4, Chuang-Han Hsu2,3, Chi-Cheng Lee2,3, Hsin Lin2,3, Arun Bansil4
1Physics, National Sun Yat-Sen University, Kaohsiung, Taiwan
2Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Singapore, Taiwan
3Physics, National University of Singapore, Singapore, Taiwan
4Physics, Northeastern University, Boston, Massachusetts, Taiwan
* presenting author:Zhi-Quan Huang,
We predict planar Sb/Bi honeycomb to harbor a two-dimensional (2D) topological crystalline insulator (TCI) phase based on first-principles computations. Although buckled Sb and Bi honeycombs support 2D topological insulator (TI) phases, their structure becomes planar under tensile strain. The planar Sb/Bi honeycomb structure restores the mirror symmetry, and is shown to exhibit non-zero mirror Chern numbers, indicating that the system can host topologically protected edge states. Our computations show that the electronic spectrum of a planar Sb/Bi nanoribbon with armchair or zigzag edges contains two Dirac cones within the band gap and an even number of edge bands crossing the Fermi level. Lattice constant of the planar Sb honeycomb is found to nearly match that of hexagonal-BN. The Sb nanoribbon on hexagonal-BN exhibits gapped edge states, which we show to be tunable by an out-of-the-plane electric field, providing controllable gating of edge state important for device applications.

Keywords: 2D topological insulators, topological phase transition, quantum spin Hall effect, electronic structures, first-principles calculations