Majorana fermions in ferromagnetic chains on the surface of bulk spin-orbit coupled $s$-wave superconductors

TL;DR

This paper proposes a robust platform for realizing Majorana fermions using ferromagnetic chains on spin-orbit coupled superconductors, avoiding fine-tuning and enabling potential topological quantum computing.

Contribution

It introduces a minimal fine-tuning method to generate Majorana fermions in ferromagnetic chains on superconductors with spin-orbit coupling, detailing their detection via STM.

Findings

Supports zero-energy Majorana modes at chain ends

Number of Majorana fermions per end depends on ferromagnetic strength

Zero-bias peaks in STM measurements indicate Majorana presence

Abstract

Majorana fermion (MF) excitations in solid state system have non-Abelian statistics which is essential for topological quantum computation. Previous proposals to realize MF, however, generally requires fine-tuning of parameters. Here we explore a platform which avoids the fine-tuning problem, namely a ferromagnetic chain deposited on the surface of a spin-orbit coupled $s$-wave superconductor. We show that it generically supports zero-energy topological MF excitations near the two ends of the chain with minimal fine-tuning. Depending on the strength of the ferromagnetic moment in the chain, the number of MFs at each end, $n$, can be either one or two, and should be revealed by a robust zero-bias peak (ZBP) of height $2ne^2/h$ in scanning tunneling microscopy (STM) measurements which would show strong (weak) signals at the ends (middle) of the chain. The role of an approximate chiral symmetry which gives an integer topological invariant to the system is discussed.