A surge of experimental and theoretical advances in the past two decades have sustained a vigorous interest in studying Majorana zero modes (MZM) in condensed matter systems. Majorana zero modes are spinless zero-energy bound excitations which form a highly degenerate ground-state manifold displaying non-Abelian braiding statistics, making this quasiparticle an attractive candidate for topological quantum computing. Beyond the potential computing applications, MZMs are of general scientific interest, combining two paradigms of condensed matter physics that have dominated research in different eras; superconductivity and topological physics. Evidence confirming the existence of these quasiparticles is mounting, with zero-bias conductance tunneling providing the strongest signature to date, but the development and utilization of other techniques is necessary to provide a smoking-gun signature of Majorana zero modes. Among the most promising proposals are schemes harnessing the quantized nature of quantum dots (QDs) coupled to MZMs, which would probe the most compelling aspects of MZMs. In this thesis, I will present the development of the Strong-Coupling Quantum Dot Microscope (SCQDM), a novel scanning quantum dot probe potentially capable of uniquely distinguishing Majorana zero modes. In particular, the SCQDM is well suited for Majorana samples that lend themselves to study with scanning probe techniques. The SCQDM utilizes a capacitance scheme, in contrast to related transport techniques, to measure the full counting statistics of electrons entering the apex quantum dot while positioned within tunneling range of a MZM. We present functional testing of the two most important aspects of the microscope: single electron counting and angstrom distance tunneling at 300 mK. In the Appendix, I will present STM results taken on topological insulator/superconductor bilayer structures, showing evidence of the topologically protected surface state (TPSS) proximitizing to the surface of the superconducting overlayer. Evidence of the Bi2Se3 TPSS leaking into a Nb overlayer will be shown, an effect we have dubbed the Dual Topological Proximity Effect (DTPE).
Read
