Charge-neutral nonlocal response in superconductor-InAs nanowire hybrid devices

TL;DR

This study uses nonlocal shot noise measurements to reveal that quasiparticle responses in superconductor-InAs nanowire devices are charge-neutral and dominated by heat transport, providing new insights into sub-gap states.

Contribution

It introduces nonlocal shot noise as a tool to analyze quasiparticle charge neutrality and heat transport in superconductor-nanowire hybrid devices, revealing new physical behavior.

Findings

Quasiparticle response is charge-neutral in trivial superconducting phase.

Thermal conductance is on the order of conductance quantum.

Sign reversals and fluctuations observed in nonlocal conductance.

Abstract

Nonlocal quasiparticle transport in normal-superconductor-normal (NSN) hybrid structures probes sub-gap states in the proximity region and is especially attractive in the context of Majorana research. Conductance measurement provides only partial information about nonlocal response composed from both electron-like and hole-like quasiparticle excitations. In this work, we show how a nonlocal shot noise measurement delivers a missing puzzle piece in NSN InAs nanowire-based devices. We demonstrate that in a trivial superconducting phase quasiparticle response is practically charge-neutral, dominated by the heat transport component with a thermal conductance being on the order of conductance quantum. This is qualitatively explained by numerous Andreev reflections of a diffusing quasiparticle, that makes its charge completely uncertain. Consistently, strong fluctuations and sign reversal are observed in the sub-gap nonlocal conductance, including occasional Andreev rectification signals. Our results prove conductance and noise as complementary measurements to characterize quasiparticle transport in superconducting proximity devices.