RADIOFREQUENCY PROPERTIES OF INHOMOGENEOUS SUPERCONDUCTORS IN LOW MAGNETIC-FIELDS

It is experimentally demonstrated how closed looped objects of inhomog eneous superconductors can exhibit quantum interference device (SQUID) behaviour. It appears that the physical origin is the ability of exce edingly small changes in magnetic field to induce macroscopic redistri butions of magnetic flux. The samples studied range from ceramic tubes of the high-temperature superconductor YBa2Cu3O7-x to thin-film tubes of ordinary metallic superconductors with artificially introduced def ects. In contrast to the ordinary SQUID, the observed period with flux in the response does not usually correspond to a single flux quantum in the geometrically calculated applied flux. This is associated with incomplete penetration of the flux lines through the tube walls.