# Zero-energy pinning of topologically-trivial bound states in multi-band semiconductor-superconductor nanowires

## TL;DR

This paper shows that trivial Andreev bound states in multi-band semiconductor-superconductor nanowires can be pinned near zero energy due to inter-band coupling and electrostatic effects, mimicking Majorana signatures in tunneling experiments.

## Contribution

It reveals that level repulsion from inter-band coupling can produce zero-energy states in trivial systems, challenging the interpretation of Majorana signatures.

## Key findings

- Zero-energy pinning occurs in inhomogeneous multi-band systems.
- Level repulsion can mimic Majorana gap signatures.
- Particle-hole asymmetric conductance features are due to trivial ABSs.

## Abstract

Recent tunneling conductance measurements on semiconductor-superconductor nanowires find zero-bias peaks to be ubiquitous across wide ranges of chemical potential and Zeeman energy. Motivated by this, we demonstrate that topologically-trivial Andreev abound states (ABSs) pinned near zero energy are produced rather generically in inhomogeneous systems with multi-band occupancy in the presence of inter-band coupling. We first investigate the inter-band coupling mechanism responsible for the pinning within a multi-band 1D toy model, then we confirm the findings using a 3D Schr\"{o}dinger-Poisson approach that incorporates the geometric and electrostatic details of the actual device. Our analysis shows that level-repulsion generated by inter-band coupling can lead to a rather spectacular pinning of the lowest-energy mode near zero energy in systems (or regions) characterized by very-short length scales ($\sim100~$nm).We show that level repulsion between the lowest energy levels can mimic the gap opening feature (simultaneous with the emergence of a near-zero energy mode) predicted to occur in Majorana hybrid systems. We also demonstrate that nearly-zero bias differential conductance features exhibiting particle-hole asymmetry are due to the presence of (topologically-trivial) ABSs pinned near zero-energy by level repulsion, not to Majorana zero modes, quasi-Majoranas, or any other low-energy mode that involves (partially) separated Majorana bound states. Our findings demonstrate the importance of understanding in detail multi-band physics and electrostatic effects in the context of the ongoing search for Majorana modes in semiconductor-superconductor heterostructures.