Masters Defense: Ida Egholm Nielsen – University of Copenhagen

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Masters Defense: Ida Egholm Nielsen

Subgap states in proximitized full-shell nanowires

The endeavour for low-decoherence quantum computing has over the past decades lead to an intense search for Majorana zero-energy modes as they provide a platform for topologically protected quantum information processing. Hybrid semiconductor-superconductor nanowires have been proposed as a possible realisation of these modes and have shown signatures consistent with the theory of Majorana modes. Tunnelling spectroscopy of the recently designed full-shell wires has revealed a zero-energy state in certain intervals of an applied axial magnetic field.  

In this thesis we expand a simple model for full-shell wires by introducing  different perturbations. These include impurities treated within the first-order Born approximation, as well as deformations that break the angular symmetry. Different concepts that are relevant for the understanding of full-shell wires will be introduced, and through appropriate approximations we will make predictions to be held up against the experimental observations. A central prediction is our calculation of the differential conductance by use of the scattering matrix formalism. We will also question the stability of a possible non-trivial topological phase and search for trivial zero-energy states that present an alternative interpretation of the experimental results.