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

TL;DR

This study demonstrates room-temperature quantum spin Hall states in Bi4Br4 nanowires using microwave impedance microscopy, revealing scalable, stable topological edge states suitable for practical electronic applications.

Contribution

It introduces a stair stepped multilayer configuration enabling robust, scalable QSH states at room temperature, overcoming previous material and structural limitations.

Findings

QSH states persist up to 300 K in Bi4Br4 nanowires

Stair stepped stacking preserves edge state decoupling

Scaling of signals confirms stair stepped origin

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.