Atomic manipulation of in-gap states in theβ−Bi2Pdsuperconductor

Electronic states in the gap of a superconductor inherit intriguing many-body properties from the superconductor. Here, we create these in-gap states by manipulating Cr atomic chains on the $\ensuremath{\beta}\ensuremath{-}\mathrm{Bi}{}_{2}\mathrm{Pd}$ superconductor. We find that the topological properties of the in-gap states can greatly vary depending on the crafted spin chain. These systems make an ideal platform for nontrivial topological phases because of the large atom-superconductor interactions and the existence of a large Rashba coupling at the Bi-terminated surface. We study two spin chains, one with atoms two lattice parameters apart and one with $\sqrt{2}$ lattice parameters. Of these, only the second one is in a topologically nontrivial phase, in agreement with the spin interactions for this geometry.