Search for Majorana fermions in multiband semiconducting nanowires

TL;DR

This paper investigates multiband semiconducting nanowires coupled with superconductors, demonstrating conditions for realizing Majorana modes, analyzing phase transitions, and assessing robustness against disorder, highlighting the advantages of multiband occupancy for Majorana detection.

Contribution

It provides an analytical phase diagram for multiband nanowires supporting Majorana modes and identifies optimal conditions for topological robustness against disorder.

Findings

Majorana modes appear when an odd number of subbands are occupied.

Multiband occupancy relaxes one-dimensional constraints and allows higher carrier densities.

A 'sweet spot' exists where the topological phase is resilient to disorder.

Abstract

We study multiband semiconducting nanowires proximity-coupled with an s-wave superconductor. We show that when odd number of subbands are occupied the system realizes non-trivial topological state supporting Majorana modes localized at the ends. We study the topological quantum phase transition in this system and analytically calculate the phase diagram as a function of the chemical potential and magnetic field. Our key finding is that multiband occupancy not only lifts the stringent constraint of one-dimensionality but also allows to have higher carrier density in the nanowire and as such multisubband nanowires are better-suited for observing the Majorana particle. We study the robustness of the topological phase by including the effects of the short- and long-range disorder. We show that in the limit of strong interband mixing there is an optimal regime in the phase diagram ("sweet spot") where the topological state is to a large extent insensitive to the presence of disorder.