Thin-film dc SQUID gradiometer using a single YBa2Cu3O7−<i>x</i> layer

Abstract

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 loops coupled directly to a small area SQUID in the center of the structure. The main advantage in comparison to magnetometers is the possibility of direct measurements in a magnetically unshielded environment. At 77 K without bias reversal technique we obtain a white noise level of about 4.5×10−5 Φ0 Hz−1/2 or 8×10−13 T cm−1 Hz−1/2 down to 10 Hz. At 1 Hz noise increases up to 6×10−12 T cm−1 Hz−1/2.