Search for Majorana Fermions in Multiband Semiconducting Nanowires

TLDR

The authors investigate multiband semiconducting nanowires coupled to an s‑wave superconductor, focusing on the topological quantum phase transition and analytically mapping the phase diagram in terms of chemical potential and magnetic field. They model the system’s topological phase by analytically deriving the phase diagram and assessing robustness against short‑ and long‑range disorder, thereby characterizing the effects of multiband occupancy and interband mixing. They find that an odd number of occupied subbands produces a non‑trivial topological state hosting Majorana modes, that multiband occupancy relaxes one‑dimensionality constraints and increases carrier density, and that strong interband mixing creates a sweet‑spot regime where the topological phase is largely disorder‑insensitive.

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.