The boundary modes of topological insulators are protected by the symmetries of the nontrivial bulk electronic states. Unless these symmetries are broken, they can give rise to novel phenomena, such as the quantum spin Hall effect in one-dimensional (1D) topological edge states, where quasiparticle backscattering is suppressed by time-reversal symmetry (TRS). Here, we investigate the properties of the 1D topological edge state of bismuth in the absence of TRS, where backscattering is predicted to occur. Using spectroscopic imaging and spin-polarized measurements with a scanning tunneling microscope, we compared quasiparticle interference (QPI) occurring in the edge state of a pristine bismuth bilayer with that occurring in the edge state of a bilayer, which is terminated by ferromagnetic iron clusters that break TRS. Our experiments on the decorated bilayer edge reveal an additional QPI branch, which can be associated with spin-flip scattering across the Brioullin zone center between time-reversal band partners. The observed QPI characteristics exactly match with theoretical expectations for a topological edge state, having one Kramer’s pair of bands. Together, our results provide further evidence for the nontrivial nature of bismuth and in particular, demonstrate backscattering inside a helical topological edge state induced by broken TRS through local magnetism.

拓扑绝缘子的边界模式受非平凡的体电子态的对称性保护。除非打破了这些对称性，否则它们会引起新的现象，例如在一维（1D）拓扑边缘状态中的量子自旋霍尔效应，其中准粒子反向散射通过时间反转对称性（TRS）得以抑制。在这里，我们研究了在不存在TRS的情况下铋的1D拓扑边缘状态的性质，预计会发生反向散射。使用光谱成像和扫描隧道显微镜进行自旋极化测量，我们比较了在原始铋双层边缘状态下发生的准粒子干扰（QPI）和在双层边缘状态下发生的准粒子干扰（QPI），该干扰以铁磁铁簇终止，打破TRS。我们在装饰双层边缘上的实验揭示了一个附加的QPI分支，该分支可能与时间反转带伙伴之间在Brioullin区中心的自旋翻转散射有关。观察到的QPI特性与具有一个Kramer一对能带的拓扑边缘状态的理论预期完全匹配。在一起，我们的结果为铋的非平凡性质提供了进一步的证据，尤其是证明了由局部磁致TRS断裂引起的螺旋拓扑边缘状态内部的反向散射。有一个克莱默的乐队。在一起，我们的结果为铋的非平凡性质提供了进一步的证据，尤其是证明了由局部磁致TRS断裂引起的螺旋拓扑边缘状态内部的反向散射。有一个克莱默的乐队。在一起，我们的结果为铋的非平凡性质提供了进一步的证据，尤其是证明了由局部磁致TRS断裂引起的螺旋拓扑边缘状态内部的反向散射。