Tunable topological states hosted by unconventional superconductors with adatoms

TL;DR

This paper proposes a new method to realize topological superconductivity using unconventional superconductors with chains of non-magnetic adatoms, enabling control of Majorana modes via magnetic fields.

Contribution

It introduces a novel platform for topological states based on unconventional superconductors and develops a mapping to lattice models for analysis.

Findings

Topological phases can be achieved by tuning Zeeman fields.

Majorana zero modes can be generated, moved, and fused.

The approach applies to complex superconductors like Sr$_2$RuO$_4$.

Abstract

Chains of magnetic atoms, placed on the surface of s-wave superconductors, have been established as a laboratory for the study of Majorana bound states. In such systems, the breaking of time reversal due to magnetic moments gives rise to the formation of in-gap states, which hybridize to form one-dimensional topological superconductors. However, in unconventional superconductors even non-magnetic impurities induce in-gap states since scattering of Cooper pairs changes their momentum but not their phase. Here, we propose a path for creating topological superconductivity, which is based on an unconventional superconductor with a chain of non-magnetic adatoms on its surface. The topological phase can be reached by tuning the magnitude and direction of a Zeeman field, such that Majorana zero modes at its boundary can be generated, moved and fused. To demonstrate the feasibility of this platform, we develop a general mapping of films with adatom chains to one-dimensional lattice Hamiltonians. This allows us to study unconventional superconductors such as Sr$_2$RuO$_4$ exhibiting multiple bands and an anisotropic order parameter.