Quasi-one-dimensional topological material Bi₄X₄(X=Br,I)

Bismuth halogenides, a family of quasi-one-dimensional (1D) materials, including α and α phases of Bi₄Br₄ and Bi₄I₄, have been predicted to exhibit rich and interesting topological properties. The single layer of Bi₄Br₄ was demonstrated to be a quantum spin Hall insulator (QSHI) with a 0.18 eV gap. Such a band gap is large enough for the observation of QSHI at room temperature. Bulk α-Bi₄Br₄ was categorized as a higher-order topological insulator and was soon examined in experiments. In addition, the α-Bi₄Br₄ exhibit simultaneously the topological phase and superconductive phase under 3.8–4.3 GPa pressure. While the single layer of Bi₄I₄ was shown to be close to the critical point of the QSHI/trivial-insulator phase transition, the α-Bi₄I₄ was considered to be a strong or weak topological insulator. In this work, we reviewed the recent progress in the topological properties of bismuth halogenides, including the theoretical calculations, angle-resolved photoemission spectroscopy, scanned tunneling microscopy analyses, quantum transport measurement and the superconducting phase transfer under pressure. We expect further research of this family material about the non-trivial superconductor and possible Majorana, room-temperature quantum transport effect and potential application in the quantum device for the electronics and information technology.