DIRECT-COUPLED 2ND-ORDER SUPERCONDUCTING QUANTUM INTERFERENCE DEVICE GRADIOMETER FROM SINGLE-LAYER OF HIGH-TEMPERATURE SUPERCONDUCTOR

We developed a noble design of the planar-type single-layer second-ord er superconducting quantum interference device (SQUID) gradiometer, an d demonstrated that the gradiometer did not respond to a uniform field or the first-order gradient of the field but responded sensitively to the second-order gradient. The device consisted of three parallel-con nected pickup loops, each of which is directly coupled to the step-edg e junction SQUID. The entire structure was made from a single layer of YBa2Cu3O7 patterned by photolithography with ion milling technique. R esponse of the device to the field was tested with three identical wir e-wound coils coupled to each loop and balancing was achieved by using a small piece of superconductor placed in the center loop. Measured o ff balance was about 0.6% for the uniform field and 1.4% for the first -order gradient, which were believed not due to intrinsic imbalance bu t mostly due to slight difference in alignment of the test coils. (C) 1998 American Institute of Physics. [S0003-6951(98)02542-X].