Superconducting junction of a single-crystalline Au nanowire for an ideal Josephson device

TL;DR

This paper demonstrates a highly transparent superconducting junction using a single-crystalline gold nanowire connected to aluminum electrodes, enabling ideal Josephson device behavior with clear supercurrent and MAR features.

Contribution

It introduces a fabrication method for a nearly ideal Josephson junction with high transparency using single-crystalline gold nanowires and aluminum electrodes.

Findings

Clear supercurrent observed below Al's Tc

Quantized voltage plateaus under microwave radiation

High contact transparency (~0.95) achieved

Abstract

We report on the fabrication and measurements of a superconducting junction of a single-crystalline Au nanowire, connected to Al electrodes. Current-Voltage characteristic curve shows clear supercurrent branch below the superconducting transition temperature of Al and quantized voltage plateaus on application of microwave radiation, as expected from Josephson relations. Highly transparent (0.95) contacts very close to an ideal limit of 1 are formed at the interface between the normal metal (Au) and the superconductor (Al). The very high transparency is ascribed to the single crystallinity of a Au nanowire and the formation of an oxide-free contact between Au and Al. The sub-gap structures of the differential conductance are well explained by coherent multiple Andreev reflections (MAR), the hallmark of mesoscopic Josephson junctions. These observations demonstrate that single crystalline Au nanowires can be employed to develop novel quantum devices utilizing coherent electrical transport.