Superconducting Quantum Interference in Twisted van der Waals Heterostructures

TL;DR

This paper demonstrates the fabrication of Josephson junctions and SQUIDs using twisted NbSe2 flakes, overcoming common issues with traditional materials, and shows their flux modulation properties depend on the twist angle.

Contribution

It introduces a dry transfer technique for creating twisted NbSe2-based Josephson junctions and SQUIDs with improved flux modulation performance.

Findings

Devices show up to 75% critical current modulation depth.

Flux modulation depth reaches approximately 1.4 mV.

Josephson dynamics are sensitive to the crystallographic misalignment.

Abstract

Modern Superconducting QUantum Interference Devices (SQUIDs) are commonly fabricated from either Al or Nb electrodes, with an in-situ oxidation process to create a weak link between them. However, common problems of such planar nano- and micro-SQUIDs are hysteretic current-voltage curves, and a shallow flux modulation depth. Here, we demonstrate the formation of both Josephson junctions and SQUIDs using a dry transfer technique to stack and deterministically misalign flakes of NbSe$_{2}$; allowing one to overcome these issues. The Josephson dynamics of the resulting twisted NbSe$_{2}$-NbSe$_{2}$ junctions are found to be sensitive to the misalignment angle of the crystallographic axes. A single lithographic process was then implemented to shape the Josephson junction into a SQUID geometry with typical loop areas of $\simeq$ 25 $\mu m^{2}$ and weak links $\simeq$ 600 nm wide. These devices display large stable current and voltage modulation depths of up to $\Delta I_{c} \simeq$ 75$\%$ and $\Delta V \simeq$ 1.4 mV respectively.