Atomic Manipulation of In-gap States on the $\beta$-Bi$_2$Pd Superconductor

TL;DR

This study demonstrates how atomic manipulation of Cr chains on $eta$-Bi$_2$Pd superconductors creates in-gap states with tunable topological properties, revealing potential for topological quantum phases.

Contribution

It shows that the topological nature of in-gap states can be controlled by atomic arrangement, highlighting a platform for exploring non-trivial topological phases.

Findings

Only the square-root-of-two lattice parameter chain is topologically non-trivial.

Large atom-superconductor interactions facilitate the creation of in-gap states.

Rashba coupling at the surface influences the topological properties.

Abstract

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 $\beta$-Bi$_2$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 non-trivial 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-parameter apart and one with square-root-of-two lattice parameters. Of these, only the second one is in a topologically non-trivial phase, in correspondence with the spin interactions for this geometry.