# Ion-irradiated YBa$_2$Cu$_3$O$_7$ Josephson arrays

## TL;DR

This study presents the design, fabrication, and testing of ion-irradiated YBa2Cu3O7 Josephson arrays with different junction spacings, revealing distinct behaviors and potential for enhanced superconducting device performance.

## Contribution

It introduces a novel array design with varying junction spacings that exhibit different electrical behaviors, including giant Shapiro steps and a new approach to increasing the I_c R_N product.

## Key findings

- Separated arrays show giant Shapiro steps at 66K.
- Closely spaced arrays behave as a single junction.
- Design may enhance Josephson junction performance.

## Abstract

We designed, fabricated and tested short one dimensional arrays of masked ion-irradiated YBa$_2$Cu$_3$O$_7$ Josephson junctions (JJ) embedded into log-periodic spiral antennas. Our arrays consist of 4 or 8 junctions separated either by 960~nm or 80~nm long areas of undamaged YBCO. Samples with distanced junctions and with closely spaced junctions showed qualitatively different behaviors. Well separated arrays demonstrated giant Shapiro steps in the hundreds-GHz band at 66K and were tested as Josephson mixers with improved impedance matching. All closely spaced arrays behaved as one junction with a lower superconducting transition temperature, hence forming a single weak link on distances up to 880~nm. Such design opens a new way to increase the I$_{c}$R$_{N}$ product of ion-irradiated junctions and we speculate that the phenomena and physics behind it might be similar to the so-called "giant" Josephson coupling observed in cuprates.