Shiba chains of scalar impurities on unconventional superconductors

TL;DR

This paper demonstrates that chains of nonmagnetic impurities on certain unconventional superconductors can host topological phases with Majorana bound states, especially when spin-rotation symmetry is broken by the pairing potential.

Contribution

It introduces a mechanism for creating topological one-dimensional superconductors using impurity chains on unconventional superconductors with broken spin-rotation symmetry.

Findings

Impurity chains can host Majorana bound states.

Topological phases can emerge even on topologically trivial superconductors.

The mechanism applies to systems with strong spin-orbit coupling.

Abstract

We show that a chain of nonmagnetic impurities deposited on a fully gapped two- or three-dimensional superconductor can become a topological one-dimensional superconductor with protected Majorana bound states at its end. A prerequisite is that the pairing potential of the underlying superconductor breaks the spin-rotation symmetry, as it is generically the case in systems with strong spin-orbit coupling. We illustrate this mechanism for a spinless triplet-superconductor p+ip and a time-reversal symmetric Rashba superconductor with a mixture of singlet and triplet pairing. For the latter, we show that the impurity chain can be topologically nontrivial even if the underlying superconductor is topologically trivial.