Bulk insulation and surface electrons' properties of Pb(Bi,Sb)2Te4 Topological Insulator

In the field of Topological Insulators (TIs), almost all the transport studies are limited to (Bi,Sb)2(Te,Se,S)3 (BSTS)TIs. For now, BSTS-TIs has the largest bulk resistivity and transport properties of surface states have been revealed in detail. However, the utilization of surface states for device application is still a bit difficult for now.
In such context, many theoretical researchers are motivated to find new TIs, and PbBi2Te4 series TIs were discovered. The topological index of Pb-TI is (1;111), which is completely different from BSTS’s (1;000). Also, PbBi2Se4 is considered to have considerably large bulk band gap of 600meV, which is higher than Bi2Se3's 300meV. However, the single phase and single crystal of PbBi2Te4 series TIs are difficult to grow, which hampers clarification of surface electrons’ nature.
In our study, we fabricated a series of Pb(Bi,Sb)2Te4 TI single crystal from off-stoichiometry mixture. By changing Bi, Sb ratio, we systematically studied the transport properties in order to enhance bulk resistivity. Precise control of Sb concentration made it possible to fabricate bulk insulating samples for the first time in this system. The results of nano-flake transport measurements and STM study to clarify surface electrons’ nature will be presented.