Nontopological zero-bias peaks in full-shell nanowires induced by flux tunable Andreev states

TL;DR

This paper shows that zero-bias peaks in full-shell nanowires are caused by flux-tunable Andreev states in junctions, not by topological Majorana modes, highlighting potential misinterpretations in experiments.

Contribution

It reveals that subgap states and zero-bias peaks in full-shell nanowires are governed by junction properties and flux effects, not by topological Majorana modes.

Findings

Longer junctions exhibit subgap states and zero-bias peaks.

Magnetic field dependence of Andreev levels can mimic Majorana signatures.

Zero-bias peaks are unrelated to topological superconductivity.

Abstract

A semiconducting nanowire fully wrapped by a superconducting shell has been proposed as a platform for obtaining Majorana modes at small magnetic fields. In this study, we demonstrate that the appearance of subgap states in such structures is actually governed by the junction region in tunneling spectroscopy measurements, and not the full-shell nanowire itself. Short tunneling regions never show subgap states, whereas longer junctions always do. This can be understood in terms of quantum dots forming in the junction and hosting Andreev levels in the Yu-Shiba-Rusinov regime. The intricate magnetic field dependence of the Andreev levels, through both the Zeeman and Little-Parks effects, may result in robust zero-bias peaks, features that could be easily misinterpreted as originating from Majorana zero modes, but are unrelated to topological superconductivity.