Planar weak-link devices from YBaCuO and BiSrCaCuO films

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Abstract
Weak-link devices were fabricated from polycrystalline thin films of YBaCuO and BiSrCaCuO. Two distinct types of weak links have been found in these devices. The first type, found in all of the YBaCuO and most of the BiSrCaCuO devices, has relatively low dynamic resistances and critical currents with nearly linear temperature dependences. The second type of weak links, found in some BiSrCaCuO films, has much larger dynamic resistances and critical current temperature dependences similar to that of a tunnel junction. Superconductivity quantum interference devices (SQUID’s) fabricated from BiSrCaCuO showed a periodic response to applied fields that is consistent with the magnitude of the flux enclosed by the SQUID loop. Significant hysteresis was found in the SQUID response, apparently indicating flux penetration into the films at relatively low fields.