Edge states and no wetting layer in ultrathin Bi(110) films grown on graphene/6H-SiC(0001)

Ultrathin Bi(110) films have attracted significant attraction recently as a potential candidate for two-dimensional topological insulators. Grown on different substrates, ultrathin Bi(110) films exhibit totally different topological properties. Clarifying charge doping from substrates and wetting layer existing or not will profoundly deepen our understanding of possible topological properties in ultrathin Bi(110) films, which are still under fierce debate. In this talk, we unambiguously demonstrate no wetting layer existing in epitaxial ultrathin Bi(110) films grown on graphene/6H-SiC(001) using low-temperature scanning tunneling microscopy/spectroscopy (STM/S). Obvious moiré pattern and (6 × 6) reconstruction originating from SiC(001) are clearly observed on the three-monolayer Bi(110) islands, confirming sharp and clean interface between graphene and Bi(110). Gapless edge states are also detected on island edges and domain boundaries, showing a signature of topological nontrivial electronic states in ultrathin Bi(110) films.