Observation of backscattering induced by magnetism in the topological hinge state of bismuth*

We have investigated the effects of time-reversal symmetry breaking on the topological hinge state of bismuth. Using spectroscopic imaging and spin-polarized measurements with an STM, we have compared quasiparticle interference (QPI) occurring in the hinge state of a pristine bismuth bilayer with that occurring in the hinge state of a bilayer, which is terminated by ferromagnetic iron clusters. Our experiments on the decorated bilayer edge reveal an additional QPI branch that 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 and, thus provide spectroscopic evidence for back scattering in the topological edge states of bismuth.