LOW-FREQUENCY EXCESS NOISE IN YBA2CU3O7-X DC SUPERCONDUCTING QUANTUM INTERFACES DEVICES COOLED IN STATIC MAGNETIC-FIELDS

We have investigated the performance of YBa2Cu3O7-x dc superconducting quantum interference devices (SQUIDs) cooled in static magnetic field s, B0, of 0.01-1 mT. For fields less than the earth's ambient field, a bout 0.05 mT, the white noise of the devices at 77 K is not materially affected. However, at a frequency f of 1 Hz the spectral density of t he 1/f noise, S(PHI) (1 Hz), at 0.05 mT increases by an order of magni tude over that for zero field. Furthermore, S(PHI) (1 Hz) scales appro ximately linearly with B0, suggesting strongly that the noise originat es in the motion of vortices in the YBCO film. This increase in noise is likely to be an issue for SQUIDs operated in the earth's field.