Topological superconductivity from first principles. II. Effects from manipulation of spin spirals: Topological fragmentation, braiding, and quasi-Majorana bound states

Recent advances in electron spin resonance techniques have allowed the manipulation of the spin of individual atoms, making magnetic atomic chains on superconducting hosts one of the most promising platform where topological superconductivity can be engineered. Motivated by this progress, we provide a detailed, quantitative description of the effects of manipulating spins in realistic nanowires by applying a first-principles-based computational approach to a recent experiment: an iron chain deposited on top of an Au/Nb heterostructure. As a continuation of the preceding paper, experimentally relevant computational experiments are performed in spin spiral chains that shed light on several concerns about practical applications and add new aspects to the interpretation of recent experiments. We explore the stability of topological zero-energy states, the formation and distinction of topologically trivial and nontrivial zero energy edge states, the effect of local changes in the exchange fields, the emergence of topological fragmentation, and the shift of Majorana zero modes along the superconducting nanowires, opening avenues toward the implementation of a braiding operation. © 2023 American Physical Society.