Flux focusing with a superconducting nano-needle for scanning SQUID susceptometry

TL;DR

This paper introduces a 3D nano-needle on a nano-SQUID to enhance flux focusing and spatial resolution in magnetic imaging, demonstrating improved performance over traditional planar devices.

Contribution

It presents a novel fabrication of a superconducting nano-needle on a nano-SQUID to improve flux focusing and spatial resolution in magnetic imaging applications.

Findings

Enhanced spatial resolution in magnetometry and susceptometry

Successful integration of 3D nano-structures with on-chip Josephson devices

Proof-of-principle demonstration of flux focusing with a nano-needle

Abstract

Nano-fabricated superconducting quantum interference device (nano-SQUID) is a direct and sensitive flux probe useful for magnetic imaging of quantum materials and mesoscopic devices. Enabled by functionalities of superconductive integrated circuits, nano-SQUID fabricated on a chip is particularly versatile but spatial resolution has been limited by its planar geometry. Here, we use femtosecond-laser 3-dimensional (3D) lithography and print a needle onto a nano-SQUID susceptometer to overcome the limit of a plane-structure. The nano-needle coated with a superconducting shell focuses the flux both from the field coil and the sample. We perform scanning imaging using such a needle-on-SQUID (NoS) device on superconducting test patterns with topographic feedback. The NoS shows improved spatial resolution in both magnetometry and susceptometry over its planarized counterpart. This work serves as a proof-of-principle for the integration and inductive coupling between superconducting 3D nano-structures and on-chip Josephson nano-devices.