Focused ion beam high T sub c superconductor dc SQUIDs

Light-ion irradiation can controllably reduce the critical current density of high-temperature superconductor thin films. Reported here is the behavior of ErBa{sub 2}Cu{sub 3}O{sub 7} films patterned into microbridge dc superconducting quantum interference device (SQUID) structures and irradiated with a rastered high-energy focused ion beam of 70 nm diameter. The resultant SQUIDs have demonstrated up to 51% critical current modulation at 46 K. Microbridges with appropriate critical currents manifest Josephson-like behavior in the form of well-defined Shapiro steps appearing with microwave radiation. The {ital I}{sub {ital c}R{ital n}} products of these microbridges are typically a few millivolts and the temperature dependence of their normal-state resistance is consistent with conduction through metallic filaments.