Majorana fermion fingerprints in spin-polarised scanning tunneling microscopy

TL;DR

This paper predicts how spin-polarised scanning tunneling microscopy can detect Majorana fermions in topological superconductors by analyzing conductance signatures influenced by spin polarization, symmetry, and phase tuning.

Contribution

It introduces a detailed theoretical analysis of Majorana fermion signatures in spin-polarized STM measurements, considering the effects of chiral symmetry and Josephson phase differences.

Findings

Zero/finite bias peaks depend on Majorana configuration

Spin polarization affects Majorana detection signatures

Tuning phase difference controls Majorana conductance signatures

Abstract

We calculate the spatially resolved tunneling conductance of topological superconductors (TSCs) based on ferromagnetic chains, measured by means of spin-polarised scanning tunneling microscopy (SPSTM). Our analysis reveals novel signatures of MFs arising from the interplay of their strongly anisotropic spin-polarisation and the magnetisation content of the tip. We focus on the deep Yu-Shiba-Rusinov (YSR) limit where only YSR bound states localised in the vicinity of the adatoms govern the low-energy as also the topological properties of the system. Under these conditions, we investigate the occurence of zero/finite bias peaks (ZBPs/FBPs) for a single or two coupled TSC chains forming a Josephson junction. Each TSC can host up to two Majorana fermions (MFs) per edge if chiral symmetry is preserved. Here we retrieve the conductance for all the accessible configurations of the MF number of each chain. Our results illustrate innovative spin-polarisation-sensitive experimental routes for arresting the MFs by either restoring or splitting the ZBP in a predictable fashion via: i) weakly breaking chiral symmetry, e.g. by the SPSTM tip itself or by an external Zeeman field and ii) tuning the superconducting phase difference of the TSCs, which is encoded in the 4$\pi$-Josephson coupling of neighbouring MFs.