Resolving the topological classification of bismuth with topological defects

Bulk boundary correspondence has been the cornerstone in the study of topological quantum materials. It has enabled the exploration of electronic bulk properties through the investigation of topological boundary modes. However, the growing diversity and profusion of topological classes has lead to ambiguity between classes sharing similar boundary phenomenology. This is the current status of bismuth, for which recent studies have suggested nontrivial classifications like strong or higher-order TI, both of which hosts 1D helical modes on their boundaries. Here, we use a novel approach to resolve the topological classification of bismuth by spectroscopically mapping the response of a topological lattice defect like screw dislocation using a scanning tunneling microscope. We find a 1D edge mode, bound to the step edges of bismuth, extending to the core of the screw dislocation without gapping out. This signifies that the edge mode binds to the topological defect, characteristic of a material with nonzero weak indices. This work paves the way for the identification of novel electronic topological phases through the study of boundary modes associated with topological defects.