Low-frequency magnetic flux noise in high-T c superconducting SQUIDs

Low-frequency magnetic flux fluctuations in high-Tc superconducting films and SQUIDs are investigated. It is shown that 1/f noise in epitaxial high-Tc superconducting samples in weak magnetic fields is attributable to discrete Josephson fluctuators, each consisting of a superconducting loop closed by weak links. It is confirmed by numerical analysis that the presence of such fluctuators can account for several unusual phenomena encountered in electronic devices utilizing high-Tc superconductors. It is noted that a junction utilizing a bicrystal interface is superior from the standpoint of minimizing the given noise mechanism.