# High-Tc superconducting detector for highly-sensitive microwave magnetometry

## TL;DR

This paper presents a high-temperature superconducting SQUID array functioning as a highly sensitive, low-dissipation microwave magnetometer capable of detecting femtotesla-level magnetic fields at GHz frequencies.

## Contribution

It introduces a scalable fabrication method for large SQUID arrays using ion irradiation, demonstrating a practical high-Tc SQIF for sensitive microwave magnetic field detection.

## Key findings

- Detects magnetic fields of a few pT at 1.125 GHz
- Achieves sensitivity of a few hundred fT/√Hz
- Operates effectively at 66 K in unshielded environment

## Abstract

We have fabricated arrays of High-T$_c$ Superconducting Quantum Interference Devices (SQUIDs) with randomly distributed loop sizes as sensitive antennas for Radio-Frequency (RF) waves. These sub-wavelength size devices known as Superconducting Quantum Interference Filters (SQIFs) detect the magnetic component of the electromagnetic field. We use a scalable ion irradiation technique to pattern the circuits and engineer the Josephson junctions needed to make SQUIDs. Here we report on a 300 SQUIDs series array with loops area ranging from $6$ to $60\ \mu m^{2}$, folded in a meander line covering a $3.5\ mm\times 8\ mm$ substrate area, made out of a $150$-nm-thick $\mathrm{YBa}_2\mathrm{Cu}_3\mathrm{O}_7$ film. Operating at a temperature $T=66\ K$ in a un-shielded magnetic environment, under low DC bias current ($I=60\ \mu A$) and DC magnetic field ($B=3\ \mu T$), this SQIF can detect a magnetic field of a few $pT$ at a frequency of $1.125\ GHz$, which corresponds to a sensitivity of a few hundreds of $fT/\sqrt{Hz}$, and shows linear response over 7 decades in RF power. This work is a promising approach for the realization of low dissipative sub-wavelength GHz magnetometers.