Experimental investigation of topological insulators and superconductors

Topological insulators are characterized by a fully gapped bulk and gapless surface states. They have ignited tremendous research activities in the field of condensed matter physics in recent years because of their theoretical research value for novel quantum phenomena and potential practical applications. However, access to the topological surface states by transport measurements in most current topological insulators remains a challenge due to the overwhelming contribution of the bulk conductivity to the charge transport. The first main topic of this thesis is therefore to reduce the contribution of the bulk conductivity in the prototypical topological insulator material Bi_2-xSb_xTe_3-ySe_y, then detect the topological surface states and investigate their transport properties. Analogously, the notion of topological insulators was generalized to topological superconductors. Topological superconductors have become a highly interesting research theme due to the hosting of Majorana zero modes at the surface, which are predicted to provide a new route to fault tolerant quantum computation. Therefore, the search for topological superconductors and the determination of their intrinsic properties is an important research topic. The second main topic of this thesis is to study two candidate topological superconductors ErPdBi and Sr_xBi₂Se₃.