Interplay of topological phases in magnetic adatom-chains on top of a Rashba superconducting surface

TL;DR

This paper explores how magnetic adatom chains on a Rashba superconductor surface can host various topological phases with Majorana fermions, influenced by magnetic order and system parameters, revealing new topological behaviors.

Contribution

It identifies the magnetic ground states and topological phases in adatom chains on Rashba superconductors, highlighting the conditions for Majorana fermions and their distinct wavefunction profiles.

Findings

Hybrid system can host one or two Majorana fermions per edge.

Different magnetic orders lead to distinct topological features.

Parameter tuning can access diverse Majorana phases.

Abstract

We investigate the topological properties and the accessible Majorana fermion (MF) phases arising in a hybrid device consisting of a chain of magnetic adatoms placed on the surface of a conventional superconductor with Rashba spin-orbit coupling (SOC). By identifying the favored classical magnetic ground state of the adatom chain, we extract the corresponding phase diagram which exhibits an interplay of ferromagnetic (FM), antiferromagnetic (AFM) and spiral orders. We determine the parameter regime for which the FM or AFM phases dominate over the spiral and additionally become stable against thermal and quantum fluctuations. For the topological analysis we focus on the FM and AFM cases and employ a low-energy effective model relying on Shiba bound states. We find that for both magnetic patterns the hybrid system behaves as a topological superconductor which can harbor one or even two MFs per edge, due to chiral symmetry. As we show, the two magnetic orderings lead to qualitatively and quantitatively distinct topological features that are reflected in the spatial profile of the MF wavefunctions. Finally, we propose directions on how to experimentally access the diverse MF phases by varying the adatom spacing, the SOC strength, or the magnetic moment of the adatoms in consideration.