Josephson diode effect in multichannel Rashba nanowires: Role of inter-subband coupling

TL;DR

This paper explores how inter-subband coupling in multichannel Rashba nanowire Josephson junctions influences the Josephson diode effect, revealing new mechanisms for nonreciprocal superconducting transport and the role of Majorana states.

Contribution

It demonstrates that inter-subband hybridization significantly alters the topological phase diagram and enhances the Josephson diode effect in realistic multichannel nanowire devices.

Findings

Inter-subband coupling modifies the topological phase diagram.

Majorana bound states enhance diode efficiency within a finite Zeeman field window.

Inter-subband coupling enables finite JDE even with Zeeman field aligned along spin-orbit direction.

Abstract

The Josephson diode effect (JDE) has attracted significant attention for enabling directional, dissipationless supercurrents, positioning Josephson junctions as promising building blocks for next-generation quantum devices. Hybrid semiconductor-superconductor nanowires provide an experimentally accessible platform for realizing the JDE and hosting Majorana bound states. However, most theoretical treatments assume the single-channel limit, whereas realistic nanowire devices are inherently multichannel due to transverse confinement. Here, we investigate the JDE in multichannel Rashba nanowire Josephson junctions, focusing on the role of inter-subband coupling. We show that subband hybridization qualitatively modifies both the topological phase diagram and the JDE response of the device. In contrast to the single-channel case, the topological phase is confined to a finite window of Zeeman fields, within which Majorana bound states strongly enhance the diode efficiency. Inter-subband coupling also enables a finite JDE even when the Zeeman field is aligned along the spin-orbit direction -- a mechanism absent in independent-channel and strictly one-dimensional nanowire systems. Furthermore, inter-subband coupling enhances spectral asymmetry and significantly increases the diode efficiency compared to single-channel junctions. These results identify inter-subband hybridization as a key ingredient for realizing and optimizing nonreciprocal superconducting transport in experimentally relevant hybrid nanowire Josephson junctions.