Low 1/<i>f</i> noise in YBa2Cu3O7 dc SQUIDs on (Y)ZrO2 bicrystal substrates

Abstract

We report low noise operation of YBa2Cu3O7 SQUIDs superconducting quantum interference devices using Josephson junctions grown on bicrystal substrates of (Y)ZrO2. Energy sensitivities measured at 10 Hz (Sε=4.5×10−29 J/Hz) were to our knowledge lower than previously reported for a YBa2Cu3O7 SQUID with practical loop size (∼40 μm). The 1/f part of the voltage noise reached a maximum at 85 K where the noise spectrum was essentially white. The 1/f noise increased both at lower temperatures due to increased critical current fluctuations (∼Ibias2.2) and at higher temperatures, where the flux noise from the film produces a peak below Tc(=89 K).