Matters Arising from S. Vaitiekenas et al., "Zero-bias peaks at zero magnetic field in ferromagnetic hybrid nanowires" Nature Physics 2021

TL;DR

This paper critiques a 2021 study claiming topological superconductivity and Majorana zero modes in ferromagnetic hybrid nanowires, proposing that trivial effects like quantum dots and stray magnetic fields could explain the observed phenomena.

Contribution

It offers an alternative, more conventional explanation for the experimental results, challenging the original interpretation of topological states.

Findings

Quantum dots could mimic zero-bias peaks in the data.

Stray magnetic fields from damaged EuS regions can produce similar effects.

Trivial effects may explain phenomena attributed to topological superconductivity.

Abstract

In 2021 Nature Physics published a paper by Vaitiekenas, Liu, Krogstrup and Marcus titled "Zero-bias peaks at zero magnetic field in ferromagnetic hybrid nanowires". The paper reports low temperature transport measurements on semiconductor InAs nanowires with two partly overlapping shells -- a shell of EuS, a magnetic insulator, and a shell of Al, a metal that becomes superconducting at temperatures below 1.2K. The paper claims that (1) the data are consistent with induced topological superconductivity and Majorana zero modes (MZMs), and (2) that this is facilitated by the breaking of the time reversal symmetry through a direct magnetic interaction with the EuS shell. In this Matters Arising, we present an alternative explanation which is based on trivial effects that are likely to appear in the reported geometry. Specifically, first, we find that data the authors present in support of the topological superconductivity claim can originate from unintended quantum dots in their devices, a widely known likely explanation that is not being discussed in the paper. Second, our analysis of the setup, supported by our numerical micromagnetic simulations, shows similar effects could be obtained due to stray magnetic fields from the region of the EuS shell damaged during Al etching. This basic picture should come before the exotic interpretation in terms of magnetic exchange interaction with a ferromagnetic insulator.