Photon assisted tunneling of high order multiple Andreev reflections in epitaxial nanowire Josephson junctions

TL;DR

This study investigates photon-assisted tunneling of multiple Andreev reflections in epitaxial nanowire Josephson junctions, revealing quantized energy sidebands and confirming effective charge transfer, advancing understanding of hybrid superconducting devices.

Contribution

It demonstrates photon-assisted tunneling of high-order MARs in epitaxial nanowire Josephson junctions and confirms the effective charge transfer through quantized energy spacings.

Findings

Observation of gate-tunable supercurrents and MARs.

Detection of photon-assisted tunneling sidebands at quantized energies.

Confirmation of effective charge $ne$ transfer via microwave frequency scaling.

Abstract

Semiconductor/superconductor hybrids exhibit a range of phenomena that can be exploited for the study of novel physics and the development of new technologies. Understanding the origin the energy spectrum of such hybrids is therefore a crucial goal. Here, we study Josephson junctions defined by shadow epitaxy on InAsSb/Al nanowires. The devices exhibit gate-tunable supercurrents at low temperatures and multiple Andreev reflections (MARs) at finite voltage bias. Under microwave irradiation, photon assisted tunneling (PAT) of MARs produces characteristic oscillating sidebands at quantized energies, which depend on MAR order, $n$, in agreement with a recently suggested modification of the classical Tien-Gordon equation. The scaling of the quantized energy spacings with microwave frequency provides independent confirmation of the effective charge $ne$ transferred by the $n^\mathrm{th}$ order tunnel process. The measurements suggest PAT as a powerful method for assigning the origin of low energy spectral features in hybrid Josephson devices.