In-gap states induced by distortion in α-bismuthene

Ultrathin Bi(110) films have attracted significant attention recently as potential two-dimensional topological insulators. Their topological band structure induces one-dimensional (1D) helical edge states inside the bulk band gap; however, modification of the density of states resulting from Bi atomic distortion has also been suggested. Here we report the distortion-modified electronic states of α-bismuthene films grown on graphene/6H-SiC(0001) by using low-temperature scanning tunneling microscopy/spectroscopy. We found that the edges along the zigzag boundary between α-bismuthene and graphene are reconstructed and distorted and that the edge states are topographically dependent. The possible trivial origin of edge states induced by distortion complicates the investigation of topological nature in α-bismuthene. Steps from the substrate, stripes, and domain boundaries also induce additional site-dependent in-gap states. Additionally, we located an inversion domain boundary across which atoms are configured in the opposite order. This defect has extended spatial distribution and 1D parabolic dispersion, and hence we suggest it to be a very good platform for further topological exploration in α-bismuthene.