The growing diversity of topological electronic classes may lead to ambiguity in the classification of materials, especially in those classes that share somewhat similar phenomenology on their boundaries. Such is the current status of bismuth that is being considered as a strong, a weak and a higher order topological insulator, all of which host helical modes on their boundaries. Here we test the response of the topological edge mode in bismuth to a topological defect in the form of a screw dislocation to resolve this ambiguity, through spatially resolved spectroscopic measurements. We find an extended edge mode, which does not show any signs of backscattering in the vicinity of the screw dislocation, reminiscent of topologically protected helical mode. Shear strain arising from the screw dislocation can easily induce topological phase transition, owing to the small gap at L point. Such proximity to criticality is by itself sufficient to induce approximate helical edge mode phenomenology observed in bismuth.

[1] Manuscript under preparation