Weak topological insulators, constructed by stacking quantum spin Hall insulators with weak interlayer coupling, offer promising quantum electronic applications through topologically non-trivial 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.

弱拓扑绝缘体由具有弱层间耦合的量子自旋霍尔绝缘体堆叠而成，通过拓扑非平凡的边缘通道提供有前景的量子电子应用。然而，目前可用的弱拓扑绝缘体是相同量子自旋霍尔层的堆叠，在面外方向上具有平移对称性，导致边缘态的沟道自由度缺失。在这里，我们研究了一种候选弱拓扑绝缘体 Bi ₄ Br ₂ I ₂，它由三个不同的量子自旋霍尔绝缘体交替堆叠，每个绝缘体都具有可调的拓扑非平凡边缘态。我们的角分辨光电子能谱和第一原理计算表明，由于层间相互作用，与不同层相关的不同狄拉克锥的交叉点处出现了能隙。这对于通过改变化学势来实现拓扑边缘态的可调性至关重要。我们的工作为未来自旋电子学应用构建可调谐量子化电导器件提供了前景。