Probing interaction effects at a topological crystalline step edge by Scanning tunneling Microscopy and Scanning tunneling Spectroscopy

Topological Crystalline Insulators (TCIs) are the class of materials in which the topological nature of electronic structure arises from crystal symmetries. With the realization of a TCI phase in Pb_1-xSn_xSe it was perceived that the step edges in TCIs can be viewed as predecessors of higher-order topology, as they embody one-dimensional (1D) edge channels embedded in an effective three-dimensional electronic vacuum emanating from the TCI. Here we use scanning tunneling microscopy and spectroscopy to investigate the behavior of these 1D step-edge channels under the influence of doping. By doping distinct 3d adatoms in Pb_1-xSn_xSe we observed that once the energy position of the 1D step-edge mode is brought close to the fermi level, a new correlation gap starts to open. Our experimental findings are rationalized in terms of enhanced interaction effects since the electron density of states is collapsed to a 1D channel. This enables us to realize a unique system to study how topology and many-body electronic effects intertwine.