Surface relaxation of topological insulators: Influence on the electronic structure

Abstract

The surface structure of topological insulators Bi${}_{2}$Te${}_{3}$(111) and a single bilayer bismuth on it was studied by low-energy electron-diffraction analysis. The topmost quintuple layer of Bi${}_{2}$Te${}_{3}$ showed only a slight relaxation ($\ensuremath{\sim}\phantom{\rule{-0.16em}{0ex}}1%$ contraction). On the other hand, the bilayer Bi was strongly distorted compared to bulk Bi (3.5 $\phantom{\rule{-0.16em}{0ex}}%$ in-plane contraction and $\ensuremath{\sim}\phantom{\rule{-0.16em}{0ex}}7%$ out-of-plane expansion). First-principles calculation reveals that this distortion has a large influence on the electronic structure and can enlarge the band gap.