Twisted van der Waals Josephson junction based on high-Tc superconductor

TL;DR

This study demonstrates the fabrication of twisted Bi-2212 van der Waals Josephson junctions revealing anisotropic superconducting properties and twist-angle-dependent Josephson coupling, advancing twistronics research with air-sensitive high-Tc superconductors.

Contribution

It introduces a novel microcleave-and-stack technique for creating atomically clean twisted vdW junctions with high-Tc superconductor Bi-2212, and explores their anisotropic Josephson effects.

Findings

Maximum Josephson coupling at 0° and 90° twist angles.

Suppression of Josephson coupling near 45° twist angle.

Agreement between experimental results and theoretical calculations for d-wave superconductivity.

Abstract

Stacking two-dimensional van der Waals (vdW) materials rotated with respect to each other show versatility for the study of exotic quantum phenomena. Especially, anisotropic layered materials have great potential for such twistronics applications, providing high tunability. Here, we report anisotropic superconducting order parameters in twisted Bi2Sr2CaCu2O8+x (Bi-2212) vdW junctions with an atomically clean vdW interface, achieved using the microcleave-and-stack technique. The vdW Josephson junctions with twist angles of 0{\deg} and 90{\deg} showed the maximum Josephson coupling, which was comparable to that of intrinsic Josephson (IJ) junctions in the bulk crystal. As the twist angle approaches 45{\deg}, Josephson coupling is suppressed, and eventually disappears at 45{\deg}. The observed twist angle dependence of the Josephson coupling can be explained quantitatively by theoretical calculation with the d-wave superconducting order parameter of Bi-2212 and finite tunneling incoherence of the junction. Our results revealed the anisotropic nature of Bi-2212 and provided a novel fabrication technique for vdW-based twistronics platforms compatible with air-sensitive vdW materials.