Focused ion beam high Tc 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 ErBa2Cu3O7 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 IcRn 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.