STM study of one-dimensional topological system and 1UC-FeSe/SrTiO3 Superconductor

Abstract

The discovery of the integer quantum hall effect has led to a lot of research on the system topology. Studies on 2D or 3D topological systems, which have been studied extensively in recent years, have improved the understanding of new physical properties that the system topology has not been known so far. Studies on 1D topological systems have also been initiated by Su-Schrieffer-Heeger(SSH), and many exotic phenomena such as the Majorana zero mode have been found so far. There are not many examples of 1D systems that have been isolated yet. Through this thesis I report that the Se atom is self-assemble on Ge (111) and is arranged in a staggered hopping structure, and its unique structure makes a system similar to polyacetylene. It has been shown that topological edge states are possibly created at both ends of the wire. In the same way, the self-assembled island as well as the one-dimensional wire were found to have a state at the edge. Besides the topological insulator, there is another high-Tc superconductor (HTSC) as another strongly correlated system. The paring mechanism in HTSC is not well known yet. Many HTSCs have been studied with STMs, but in this paper we have studied FeSe / SrTiO3(100), an interface induced thin film superconductor first reported in Xue group in 2012. Two-dimensional high-temperature superconductors and the unusually high superconducting phase transition temperatures only appear on SrTiO3 or Titanate substrates have led to a number of studies on the mechanism of this exotic phenomenon. I observed at the dopant state while adjusting the doping level in this article, and I studied at how its ordering contributes to the formation of high Tc. We also studied the bosonic mode which makes pairing based on the Migdal-Eliashberg model.