Scanning probe methods such as scanning tunneling microscopy (STM) and subsurface charge accumulation imaging (SCAI) are very powerful and important tools to investigate the electronic effects near the interfaces of exotic materials. For this dissertation, the primary material studied is a three-dimensional topological insulator, which has been discovered in recent years to harbor a great deal of novel physical phenomenon. The primary feature of note with these materials is their intrinsic spin-orbit coupling, which gives rise to the surface states where the spin and momentum of the conducting electrons are locked in surprising ways to one another. Specifically, the dispersion diagram shows two branches with linear energy versus wave number crossing the semiconductor gap to form a Dirac cone feature; these conducting states reside on the surface and are known as topological surface states (TSS). This state is topologically protected by time-reversal symmetry in that these conducting surface states are robust against scattering from non-magnetic defects.In this dissertation, I will present STM results for superconductor/topological insulator interfaces, in which the superconductor induces superconductivity into the topological surface states. Superconductivity is caused by the pairing of electrons into bosons which are known as Cooper pairs, and is yet another phenomenon that involves rather intricate spin and momentum interactions. In these measurements, we observed oscillatory behavior near the interfaces as well as a surprising reverse proximity effect, in which the topological surface states appear to leak into the superconducting material as well. In the Appendix, I will alsopresent STM and SCAI results taken at conventional insulator/topological insulator interfaces, where the TSS is predicted to change locations based on the conventional insulator material deposited on the surface in an effect known as the “dual” proximity effect. In particular, we investigate the interface of ZnSe and Bi2Te3. While there has been no theoretical prediction for this specific interface, our results show that the TSS remains at the interface and does not change location as a function of bias voltage. Even though these results are preliminary, they set the stage for interesting and important measurements in the future.
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