YBa2Cu3O7-δ Nano-SQUIDs Fabricated by Focused Helium Ion Beam Direct Writing

We successfully fabricated high-transition temperature $(\mathrm{high}-T_{C})$ nano-scale superconducting quantum interference devices (nano-SQUIDs) by using a 32-keV focused helium ion beam (FHIB). The $\sim 0.5$ nm beam of the FHIB was used to disorder the crystaline lattice of YBa2Cu $3\mathrm{O}_{7-\delta}$ (YBCO) causing disorder that converts the material from superconductor to insulator at high dose. The SQUID loop size was 400 nm x 400 nm, with 200-nm wide Josephson junctions. Devices operated over a wide range of temperatures from 50 to 4 K and exhibited large voltage modulation with magnetic field as high as 500 $\mu \mathrm{V}$.