Supercurrent in van der Waals Josephson junction.

Satoru Masubuchi,Sei Morikawa,Tomoki Machida,Yohta Sata,Naoto Yabuki,Rai Moriya,Miho Arai

doi:10.1038/ncomms10616

Abstract

Supercurrent flow between two superconductors with different order parameters, a phenomenon known as the Josephson effect, can be achieved by inserting a non-superconducting material between two superconductors to decouple their wavefunctions. These Josephson junctions have been employed in fields ranging from digital to quantum electronics, yet their functionality is limited by the interface quality and use of non-superconducting material. Here we show that by exfoliating a layered dichalcogenide (NbSe2) superconductor, the van der Waals (vdW) contact between the cleaved surfaces can instead be used to construct a Josephson junction. This is made possible by recent advances in vdW heterostructure technology, with an atomically flat vdW interface free of oxidation and inter-diffusion achieved by eliminating all heat treatment during junction preparation. Here we demonstrate that this artificially created vdW interface provides sufficient decoupling of the wavefunctions of the two NbSe2 crystals, with the vdW Josephson junction exhibiting a high supercurrent transparency.

Highlights

Supercurrent flow between two superconductors with different order parameters, a phenomenon known as the Josephson effect, can be achieved by inserting a nonsuperconducting material between two superconductors to decouple their wavefunctions
A van der Waals (vdW) heterostructure provides an extra degree of freedom that is not possible to achieve in conventional heterostructures, namely, controlling the relative twist angle between the crystals at the vdW interface
Layered dichalcogenide 2H-NbSe2 was selected as the superconductor material, as it has unique properties that make it ideally suited to a vdW Josephson junction

Summary

Introduction

Supercurrent flow between two superconductors with different order parameters, a phenomenon known as the Josephson effect, can be achieved by inserting a nonsuperconducting material between two superconductors to decouple their wavefunctions. The micromechanical exfoliation of graphene from bulk graphite using Scotch tape, and its deposition on Si substrates[1], has driven extensive research into the field of two-dimensional (2D) crystals, extending the field beyond graphene to include h-BN and transition metal dichalcogenides In their bulk form, these exhibit a layered structure in which each individual layer is connected to its neighbours by van der Waals (vdW) forces, making it easy to create 2D crystals by cleaving at the vdW interface. Many high-performance electronic devices based on a vdW heterostructure have already been demonstrated, including vertical field-effect transistors[4,5], devices exhibiting strong light–matter interaction[6,7] and ballistic Josephson junctions[8] These outstanding properties are made possible by an absence of dangling bonds and lattice mismatch at the interface, which can prevent interface defects and inter-diffusion.

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Results

Conclusion