Towards Layer-Selective Quantum Spin Hall Channels in Weak Topological Insulator Bi4Br2I2

TL;DR

This paper investigates Bi4Br2I2, a weak topological insulator with layered quantum spin Hall insulators, demonstrating tunable edge states and energy gaps crucial for spintronic device applications.

Contribution

It introduces Bi4Br2I2 as a novel weak topological insulator with layered QSH insulators, enabling tunable edge states through interlayer interactions.

Findings

Energy gaps open at Dirac cone crossings due to interlayer interactions.

Tunable topological edge states are achieved by adjusting the chemical potential.

Bi4Br2I2 offers potential for quantized conductance devices in spintronics.

Abstract

Weak topological insulators, constructed by stacking quantum spin Hall insulators with weak interlayer coupling, offer promising quantum electronic applications through topologically nontrivial edge channels. However, the currently available weak topological insulators are stacks of the same quantum spin Hall layer with translational symmetry in the out-of-plane direction, leading to the absence of the channel degree of freedom for edge states. Here, we study a candidate weak topological insulator, Bi4Br2I2, which is alternately stacked by three different quantum spin Hall insulators, each with tunable topologically non-trivial edge states. Our angle-resolved photoemission spectroscopy and first-principles calculations show that an energy gap opens at the crossing points of different Dirac cones correlated with different layers due to the interlayer interaction. This is essential to achieve the tunability of topological edge states as controlled by varying the chemical potential. Our work offers a perspective for the construction of tunable quantized conductance devices for future spintronic applications.