Zero-energy Andreev bound states from quantum dots in proximitized Rashba nanowires

TL;DR

This paper demonstrates that trivial quantum dots in Rashba nanowires can host zero-energy Andreev bound states that mimic topological Majorana states, challenging their use as topological signatures.

Contribution

The study provides an analytical and numerical analysis showing trivial Andreev bound states can be pinned near zero energy without topological superconductivity, highlighting a non-topological origin of zero-bias peaks.

Findings

Zero-energy Andreev bound states occur in trivial quantum dots.

Pinning of states is independent of topological phases.

Numerical simulations confirm analytical predictions.

Abstract

We study an analytical model of a Rashba nanowire that is partially covered by and coupled to a thin superconducting layer, where the uncovered region of the nanowire forms a quantum dot. We find that, even if there is no topological superconducting phase possible, there is a trivial Andreev bound state that becomes pinned exponentially close to zero energy as a function of magnetic field strength when the length of the quantum dot is tuned with respect to its spin-orbit length such that a resonance condition of Fabry-Perot type is satisfied. In this case, we find that the Andreev bound state remains pinned near zero energy for Zeeman energies that exceed the characteristic spacing between Andreev bound state levels but that are smaller than the spin-orbit energy of the quantum dot. Importantly, as the pinning of the Andreev bound state depends only on properties of the quantum dot, we conclude that this behavior is unrelated to topological superconductivity. To support our analytical model, we also perform a numerical simulation of a hybrid system while explicitly incorporating a thin superconducting layer, showing that all qualitative features of our analytical model are also present in the numerical results.