Quasi-one Dimensional Topological Insulator -Se wires on Ge (111) surface

Topological insulator studies have been done mainly in 2D or 3D systems. However, topological orders can also be defined and preserved in certain one-dimensional chains. We have found a system, Se wires on a Ge(111) surface, that behaves as a quasi-one dimensional topological insulator. The system was fabricated by molecular beam epitaxy and measured by scanning tunneling microscopy. Within the chain, the gap is large while edge states are present at the ends of wires. This system can be understood by extended Su-Schrieffer-Heeger model that successfully explained the conductivity of ploy-acetylene chains. The origin of the topological edge states in this chain is confirmed by the scanning tunneling microscopy results and the density functional calculations. Moreover, we observed defect induced edge states in the chain which can also be described along with the topological insulator model.