THIN-FILM DC SQUID GRADIOMETER USING A SINGLE YBA2CU3O7-X LAYER

A dc SQUID gradiometer with a large effective pickup area using only a single YBa2Cu3O7-x layer and step-edge Josephson junctions on SrTiO3 substrate has been prepared. The planar gradiometer consists of two lo ops coupled directly to a small area SQUID in the center of the struct ure. The main advantage in comparison to magnetometers is the possibil ity of direct measurements in a magnetically unshielded environment. A t 77 K without bias reversal technique we obtain a white noise level o f about 4.5 X 10(-5) PHI0 Hz-1/2 or 8 X 10(-13) T cm-1 Hz-1/2 down to 10 Hz. At 1 Hz noise increases up to 6 X 10(-12) T cm-1 Hz-1/2.