In-gap States Induced by Distortion and Topology in Ultrathin Bi(110) Films

Ultrathin Bi(110) films have attracted significant attention recently as a potential candidate for two-dimensional topological insulators. The topological band structure induces one-dimensional (1D) helical edge states inside bulk band gap; however, the modification of density of states on Bi atomic distortion has also been suggested. Here, we report the distortion modified electronic states of two-monolayer Bi(110) films grown on graphene/6H-SiC(0001) by using low-temperature scanning tunneling microscopy/spectroscopy. We found that the edge states are locally topographic dependent and most probably originate from distortion, which thereby gives an illusion of the appearance of nontrivial edge states. Steps from substrate, stripes and domain boundaries also induce additional site-dependent in-gap states. Besides, we located an inversion domain boundary across which atoms are configured in opposite order. The defect has extended spatial distribution and 1D parabolic energy dispersion. Hence, we suggest this defect as a very potential candidate for nontrivial 1D states.