High-resolution studies of the Majorana atomic chain platform

TL;DR

This study uses high-resolution STM to investigate Majorana quasiparticles in Fe atomic chains on Pb, revealing a stable zero bias peak with a distinctive spatial pattern and supporting the topological superconductor model.

Contribution

The paper provides the first high-resolution measurements showing the stability and spatial structure of MQPs in atomic chains, confirming theoretical predictions.

Findings

Zero bias peak shows no splitting, indicating stable MQPs.

Distinctive 'double eye' spatial pattern observed in ZBP.

Superconducting tip measurements support particle-hole symmetry of MQPs.

Abstract

Ordered assemblies of magnetic atoms on the surface of conventional superconductors can be used to engineer topological superconducting phases and realize Majorana fermion quasiparticles (MQPs) in a condensed matter setting. Recent experiments have shown that chains of Fe atoms on Pb generically have the required electronic characteristics to form a 1D topological superconductor and have revealed spatially resolved signatures of localized MQPs at the ends of such chains. Here we report higher resolution measurements of the same atomic chain system performed using a dilution refrigerator scanning tunneling microscope (STM). With significantly better energy resolution than previous studies, we show that the zero bias peak (ZBP) in Fe chains has no detectable splitting from hybridization with other states. The measurements also reveal that the ZBP exhibits a distinctive 'double eye' spatial pattern on nanometer length scales. Theoretically we show that this is a general consequence of STM measurements of MQPs with substantial spectral weight in the superconducting substrate, a conclusion further supported by measurements of Pb overlayers deposited on top of the Fe chains. Finally, we report experiments performed with superconducting tips in search of the particle-hole symmetric MQP signature expected in such measurements.