Superconducting Quantum Interference in Twisted van der Waals Heterostructures

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.