  One-dimensional systems comprising s-wave superconductivity with meticulously
tuned magnetism and spin-orbit coupling can realize topologically gapped
superconductors hosting Majorana edge modes whose stability is determined by
the gap's size. The ongoing quest for larger topological gaps evolved into a
material science issue. However, for atomic spin chains on superconductor
surfaces, the effect of the substrate's spin-orbit coupling on the system's
topological gap size is largely unexplored. Here, we introduce an atomic layer
of the heavy metal Au on Nb(110) which combines strong spin-orbit coupling and
a large superconducting gap with a high crystallographic quality enabling the
assembly of defect-free Fe chains using a scanning tunneling microscope tip.
Scanning tunneling spectroscopy experiments and density functional theory
calculations reveal ferromagnetic coupling and ungapped YSR bands in the chain
despite of the heavy substrate. By artificially imposing a spin spiral state
our calculations indicate a minigap opening and zero-energy edge state
formation. The presented methodology paves the way towards a material screening
of heavy metal layers on elemental superconductors for ideal systems hosting
Majorana edge modes protected by large topological gaps.
