Delocalized states in three-terminal superconductor-semiconductor nanowire devices

TL;DR

This study investigates the nature of electron states in three-terminal superconductor-semiconductor nanowire devices, identifying delocalized and localized states, and explores their implications for realizing Majorana zero modes.

Contribution

It provides experimental evidence of delocalized and localized states in nanowire devices and links these states to subband origins, informing strategies to achieve Majorana zero modes.

Findings

Delocalized states observed on both ends at high magnetic fields.

Localized states are confined near tunnel barriers.

No correlated subgap resonances found, challenging Majorana hypotheses.

Abstract

We fabricate three-terminal hybrid devices with a nanowire segment proximitized by a superconductor, and with two tunnel probe contacts on either side of that segment. We perform simultaneous tunneling measurements on both sides. We identify some states as delocalized above-gap states observed on both ends, and some states as localized near one of the tunnel barriers. Delocalized states can be traced from zero to finite magnetic fields beyond 0.5 T. In the parameter regime of delocalized states, we search for correlated subgap resonances required by the Majorana zero mode hypothesis. While both sides exhibit ubiquitous low-energy features at high fields, no correlation is inferred. Simulations using a one-dimensional effective model suggest that delocalized states may belong to lower one-dimensional subbands, while the localized states originate from higher subbands. To avoid localization in higher subbands, disorder may need to be further reduced to realize Majorana zero modes.