Local and non-local quantum transport due to Andreev bound states in finite Rashba nanowires with superconducting and normal sections

TL;DR

This paper investigates Andreev bound states in finite Rashba nanowires with partial superconducting coverage, showing that zero-bias peaks and gap signatures can mimic Majorana states without topological phases.

Contribution

It demonstrates that correlated zero-bias peaks and gap signatures in conductance measurements can occur in non-topological regimes, challenging their use as definitive Majorana indicators.

Findings

Zero-bias peaks can be pinned over a wide magnetic field range.

Finite-size effects cause ABS to be delocalized, affecting conductance.

Non-topological ABS can mimic Majorana signatures in experiments.

Abstract

We analyze Andreev bound states (ABSs) that form in normal sections of a Rashba nanowire that is only partially covered by a superconducting layer. These ABSs are localized close to the ends of the superconducting section and can be pinned to zero energy over a wide range of magnetic field strengths even if the nanowire is in the non-topological regime. For finite-size nanowires (typically $\lesssim 1$ $\mu$m in current experiments), the ABS localization length is comparable to the length of the nanowire. The probability density of an ABS is therefore non-zero throughout the nanowire and differential-conductance calculations reveal a correlated zero-bias peak (ZBP) at both ends of the nanowire. When a second normal section hosts an additional ABS at the opposite end of the superconducting section, the combination of the two ABSs can mimic the closing and reopening of the bulk gap in local and non-local conductances accompanied by the appearance of the ZBP. These signatures are reminiscent of those expected for Majorana bound states (MBSs) but occur here in the non-topological regime. Our results demonstrate that conductance measurements of correlated ZBPs at the ends of a typical superconducting nanowire or an apparent closing and reopening of the bulk gap in the local and non-local conductance are not conclusive indicators for the presence of MBSs.