Experimental detection of vortices in magic-angle graphene

TL;DR

This study demonstrates vortex detection in magic-angle twisted graphene using a gate-tuned Josephson junction, revealing vortex dynamics and fundamental superconducting properties.

Contribution

We developed a vortex sensor based on a Josephson junction in magic-angle graphene, enabling direct observation of vortex behavior and measurement of key superconducting parameters.

Findings

Fraunhofer-like critical current pattern observed

Vortices jump into and out of leads, causing shifts

Fast switching between superconducting and normal states

Abstract

The tunability of superconducting magic-angle twisted-layer graphene films elevates this material system to a promising candidate for superconducting electronics. We implement a gate-tuned Josephson junction in a magic-angle twisted four-layer graphene film. Field-dependent measurements of the critical current show a Fraunhofer-like pattern that differs from the standard pattern with characteristics typical for a weak transverse screener. We observe sudden shifts associated with vortices jumping into and out of the leads. By tuning the leads to the edge of the superconducting dome, we observe fast switching between superconducting and normal states, an effect associated with vortex dynamics. Time-dependent measurements provide us with the vortex energy scale and an estimate for the London penetration depth, in agreement with recent kinetic inductance measurements on twisted graphene films. Our results prove the utility of our junction as a sensor for vortex detection, allowing us to extract fundamental properties of the 2D superconductor.