Optimizing proximitized magnetic topological insulator nanoribbons for robust Majorana bound states

Proximitized magnetic topological insulator nanoribbons (PMTINRs) are a potential platform for the realization of the Majorana bound states (MBS). Here, we present an approach based on a figure of merit, for optimizing PMTINRs and similar superconductor-topological insulator heterostructures for Majorana bound states. Both bulk and effective surface-state models are used to capture the low-energy electronic spectrum, with accurate model parameters extracted from ab initio calculations. We construct a realistic description of PMTINRs in a tight-binding framework, and with numerical simulations we resolve their spectral properties in detail. Particular attention is given to the thin-film limit, where theoretical results have been conflicting on the topology of the hybridization gap. Magnetic and nonmagnetic disorder, interface induced band-bending effects, as well as device imperfections, can all be detrimental to the formation of MBSs in PMTINRs. Based on our numerical results, we clarify how PMTINRs can be optimized, e.g. the strength of magnetization in relation with the film thickness, for obtaining a sizable topological superconducting gap and spatially well-separated MBSs that are robust against such effects.