YBa${}_2$Cu${}_3$O${}_7$ nano-constriction Josephson junctions and SQUIDs fabricated by focused helium-ion-beam irradiation

By focused $30\mathrm{k}\mathrm{e}\mathrm{V}$ He ion beam irradiation, epitaxially grown YBa${}_2$Cu${}_3$O${}_7$ (YBCO) thin films can be driven from the superconducting to the insulating state with increasing irradiation dose. A properly chosen dose suppresses superconductivity down to $4\mathrm{K}$, while crystallinity is still preserved. With this approach we create areas of normal-conducting YBCO that can be used to define resistively shunted constriction-type Josephson junctions (cJJs) on the nanometer scale. We also demonstrate that the fabricated cJJs can be incorporated in direct current superconducting quantum interference devices and can be used as detector junctions in THz antennas.