Magnet Superconductor Hybrid Systems

The ability to create, detect, and manipulate Majorana zero modes (MZMs) in nanoscopic topological superconductors is necessary for the realization of topology-based devices. Magnet-superconductor Hybrid (MSH) systems, consisting of magnetic adatoms deposited on the surface of s-wave superconductors, are a promising candidate for the engineering of topological superconductivity, as they possess the great advantage of being accessible via scanning probe techniques. We identify the unique properties of MZMs and topological superconductivity and develop new methods for quantum engineering topological superconductivity using MSH systems. We demonstrate the robustness of the topological superconducting phases in MSH systems for different disorder effects. We show that it is possible to identify the system’s topological invariant, the Chern number, in real space by attaching networks of magnetic adatom chains to an island of magnetic adatoms and counting the number of MZMs. We investigate the rich topological superconducting phase diagrams of MSH systems with non-collinear magnetic structures. MSH systems containing a magnetic skyrmion lattice are shown to have the ability to be tuned between different topological superconducting phases with an external magnetic field, opening a path for the quantum engineering and exploration of topological superconductivity. We study the experimental realization of an MSH system, nanoscale monolayer Fe islands grown on the surface of the s-wave superconductor, Re. We show that the insertion of an atomically thin oxide separation layer between the magnetic Fe island and the superconducting Re surface is crucial for the emergence of topological superconductivity. Finally, we propose a mechanism for the emergence of topological superconductivity in FeSe0.45Te0.55 by demonstrating that the interplay between the s±-wave symmetry from the superconducting gap, surface magnetism, and Rashba spin-orbit interaction gives rise to several topological superconducting phases and explains a series of experimental observations such as the emergence of MZMs in the center of vortex cores, at the end of line defects, as well as the edges of certain types of domain walls.