Erhardt Jonas, Iannetti Mattia, Dominguez Fernando, Hankiewicz Ewelina M, Trauzettel Björn, Profeta Gianni, Di Sante Domenico, Sangiovanni Giorgio, Moser Simon, Claessen Ralph
Physikalisches Institut, Universität Würzburg, D-97074, Würzburg, Germany.
Würzburg-Dresden Cluster of Excellence ct.qmat, Universität Würzburg, D-97074, Würzburg, Germany.
Nat Commun. 2025 Sep 2;16(1):8209. doi: 10.1038/s41467-025-63572-2.
Spin-momentum-locked edge states of quantum spin Hall insulators provide a compelling platform for spintronic applications, owing to their intrinsic protection against backscattering from non-magnetic disorder. This protection emerges from time-reversal symmetry, which pairs Kramers partners of helical edge modes with opposite spin and momentum, thereby strictly forbidding elastic single-particle backscattering within the pair. Yet, contrary to the idealized notion of linear edge bands, the non-monotonic dispersions of realistic materials can host multiple Kramers pairs, reintroducing backscattering channels between them without violating time-reversal symmetry. Here, we investigate inter-Kramers pair backscattering in the non-linear edge bands of the quantum spin Hall insulator indenene, highlighting a critical aspect of edge state stability. Using quasiparticle interference in scanning tunneling spectroscopy - a direct probe of backscattering - we observe intra-band coupling between different Kramers pairs, while energy regions with only a single Kramers pair remain strictly protected. Supported by theoretical analysis, our findings provide an unprecedented experimental demonstration of edge state backscattering fully consistent with their underlying topological protection. This insight has profound implications for numerous quantum spin Hall insulator candidates, emphasizing that the mere presence of gap-traversing edge modes does not inherently guarantee their protection against backscattering.
量子自旋霍尔绝缘体的自旋动量锁定边缘态为自旋电子学应用提供了一个极具吸引力的平台，这得益于它们对非磁无序引起的背散射具有内在保护作用。这种保护源于时间反演对称性，它将具有相反自旋和动量的螺旋边缘模式的克莱默斯对配对，从而严格禁止该对内部的弹性单粒子背散射。然而，与线性边缘带的理想化概念相反，实际材料的非单调色散可以容纳多个克莱默斯对，在不违反时间反演对称性的情况下重新引入它们之间的背散射通道。在这里，我们研究了量子自旋霍尔绝缘体茚中克莱默斯对之间的背散射，突出了边缘态稳定性的一个关键方面。利用扫描隧道谱中的准粒子干涉——一种背散射的直接探测方法——我们观察到不同克莱默斯对之间的带内耦合，而只有单个克莱默斯对的能量区域仍然受到严格保护。在理论分析的支持下，我们的发现提供了一个前所未有的边缘态背散射实验演示，与它们潜在的拓扑保护完全一致。这一见解对众多量子自旋霍尔绝缘体候选材料具有深远意义，强调仅存在跨越能隙的边缘模式并不能固有地保证它们免受背散射的影响。
