High Tc superconducting multilayers for SQUID magnetometers

Thin-film multilayers of YBa2Cu3O7-x (YBCO) and insulating materials such as SrTiO3, MgO and CeO2 are grown in situ by laser deposition. Appropriate multilayers are used to produce bi-epitaxial grain boundary Josephson junctions, insulating crossovers - two overlapping YBCO films with an intervening inulating film, and superconducting vias - a superconducting connection between the two YBCO films via a window in the insulator. The bi-epitaxial junctions are incorporated in d.c. SQUIDs (Superconducting QUantum Interference Devices), and the crossovers and vias enable one to fabricate superconducting, multiturn flux transformers. Coupled together, the SQUID and flux fransformer from a magnetometer that, operating in liquid notrogen, has achieved a sensitivity of 0.6 pT Hz-1/2 at 10 Hz. We have used such a magnetometer to obtain magnetocardiograms. (orig.)