YBa${}_2$Cu${}_3$O${}_7$ Josephson junctions and SQUIDs defined by focused He ion beam irradiation

The invention of the He ion microscope (HIM) with sub-nm spatial resolution offers exciting perspectives, not only for high-resolution imaging of surfaces, but also for their nanoscale modification. For epitaxially grown thin films of the high-T${}_c$ cuprate superconductor YBa${}_2$Cu${}_3$O${}_7$ (YBCO), He focused ion beam (He-FIB) irradiation can be used to directly write Josephson junction (JJ) barriers into the material by driving locally the material into the insulating state. In addition to the fabrication of such beam-induced barrier junctions (bJJs), He-FIB irradiation can also be used to pattern YBCO films on the nanoscale, without removing material. This may provide an alternative way to define insulating areas for nanoSQUID fabrication. Here, we will present our recent progress in the fabrication of He-FIB-induced bJJs and SQUIDs as well as the analysis of their electric transport and noise properties, in particular with respect to the possible control of the critical current density of bJJs by variation of the He-FIB dose.