Designing Nanomagnet Arrays for an Engineered Spin-Orbit Gap in Si

Materials with strong spin-orbit coupling (SOC) are required for a variety of proposed quantum computing and spintronic devices. While bulk Si does not have a usable SOC, nanomagnet arrays (NMAs) can create an effective SOC-induced gap in Si/SiGe nanowires by producing a spatially rotating magnetic field. We consider in detail how realistic magnet geometry, strength, and polarization affect the spin-orbit gap. After carefully modeling magnetic fields from the NMAs, band structure calculations indicate which designs are feasible. We find that some previously proposed designs do not result in a meaningful spin-orbit gap. By optimizing device geometry, we propose experimentally realizable designs.