From Josephson diodes to constriction-type Josephson junctions and nanoSQUIDs – a spectrum of high-T_c YBCO nano-devices created by focused He ion beam irradiation

A focused helium ion beam (He-FIB) is a highly versatile tool to modify properties of YBa₂Cu₃O₇ (YBCO) thin films on the nanoscale. With different irradiation doses and geometries one can create various elements, e.g. Josephson barriers or normal resistors (medium-dose) or highly insulating amorphous walls or SQUID holes (high-dose). We used electric transport measurements and transmission electron microscopy analysis to provide useful insights into the effects of He-FIB irradiation with variable dose. By combining the elements mentioned above one can create various nano-devices. E.g., we have used Josephson junctions with He-FIB-induced barriers (bJJs) and insulating walls, to implement Josephson diodes with a huge asymmetry of critical currents up to ~7 (at optimum magnetic field and 4.2 K) [1], which can operate up to ~40 K. Moreover, He-FIB-created normal resistors turned out to be useful elements in bJJ arrays to provoke the mutual synchronization of AC Josephson currents of nearby bJJs connected in series. Finally, we present a new technique for creating constriction-type Josephson junctions (cJJs) with lateral size <10 nm. By embedding two cJJs in a SQUID loop, we realized YBCO nanoSQUIDs which can be highly suitable for scanning probe microscopy on the nm scale.

[1] https://arxiv.org/abs/2408.01521