Fully in-situ InAs nanowire Josephson junctions by selective-area growth and shadow evaporation

TL;DR

This paper presents a novel in-situ fabrication method for InAs nanowire Josephson junctions with Nb electrodes, achieving high interface quality, controllable supercurrent, and operation under strong magnetic fields, advancing quantum circuit applications.

Contribution

The study introduces a shadow evaporation technique for in-situ Nb/InAs nanowire junctions, enabling high transparency, clean interfaces, and operation at magnetic fields over 1 Tesla.

Findings

Clear Josephson supercurrent observed and gate-controlled.

High junction transparency indicated by excess current.

Supercurrent maintained beyond 1 Tesla magnetic field.

Abstract

Josephson junctions based on InAs semiconducting nanowires and Nb superconducting electrodes are fabricated in-situ by a special shadow evaporation scheme for the superconductor electrode. Compared to other metallic superconductors such as Al, Nb has the advantage of a larger superconducting gap which allows operation at higher temperatures and magnetic fields. Our junctions are fabricated by shadow evaporation of Nb on pairs of InAs nanowires grown selectively on two adjacent tilted Si (111) facets and crossing each other at a small distance. The upper wire relative to the deposition source acts as a shadow mask determining the gap of the superconducting electrodes on the lower nanowire. Electron microscopy measurements show that the fully in-situ fabrication method gives a clean InAs/Nb interface. A clear Josephson supercurrent is observed in the current-voltage characteristics, which can be controlled by a bottom gate. The excess current of 0.68 indicates a high junction transparency. Under microwave radiation, pronounced integer Shapiro steps are observed suggesting a sinusoidal current-phase relation. Owing to the large critical field of Nb, the Josephson supercurrent can be maintained to magnetic fields exceeding 1 T. Our results show that in-situ prepared Nb/InAs nanowire contacts are very interesting candidates for superconducting quantum circuits requiring large magnetic fields.