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arXiv · 2602.09660

Direct Visualization of Room-temperature Stair-stepped Quantum Spin Hall States in Bi4Br4

Zhiqiang Hu·Yuqi Zhang·Yuyang Wang·Kebin Xiao·Xiang Li·Zhiwei Wang·Huaixin Yang·Yugui Yao·Qi-Kun Xue·Wei Li
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Abstract

Topological insulators host exotic quantum phenomena such as the quantum spin Hall (QSH) effect, which enables dissipationless one-dimensional edge conduction. Realizing such states at room temperature and on a macroscopic scale is essential for energy-efficient electronics and quantum technologies, yet remains a fundamental challenge due to material limitations. Here, using microwave impedance microscopy, we directly visualize robust QSH states persisting up to 300 K in {\alpha}-Bi4Br4 nanowires. This stability and scalability are enabled by a stair stepped stacking configuration, a multilayer geometry in which QSH edge states from individual layers remain spatially decoupled. This configuration circumvents the stringent alignment and layer number constraints of previous proposals, allowing robust stair-stepped QSH (SS-QSH) conduction in structures several micrometers long and hundreds of nanometers high. Magnetic field and temperature dependent measurements confirm their intrinsic topological nature. Crucially, the SS-QSH and bulk signals scale with nanowire height, verifying the stair stepped origin. Our results are also successfully reproduced by finite-element analysis simulations. This work establishes {\alpha} Bi4Br4 as a practical platform for high temperature topological electronics and demonstrates a generalizable stacking strategy for designing scalable QSH systems.

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Zhiqiang Hu, Yuqi Zhang, Yuyang Wang, Kebin Xiao, Xiang Li, Zhiwei Wang, Huaixin Yang, Yugui Yao, Qi-Kun Xue, Wei Li. 2026-02-10. Direct Visualization of Room-temperature Stair-stepped Quantum Spin Hall States in Bi4Br4. https://arxiv.org/abs/2602.09660

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