Low-Noise YBa₂Cu₃O₇ dc-SQUIDS and Magnetometers Using Step-Edge Junctions

Superconducting quantum interference devices (SQUlDs) using YBa₂Cu₃O₇step-edge grain boundary junctions on LaAlO₃ substrates were fabricated. The I-V and V-Ф characteristics of these step-junction dc-SQUIDS were studied. A modulation voltage exceeding 16μV was attained with L_s = 60pH at 77K. At 77K, a square washer configuration with inductance L_s = 150pH yields flux noise of about 5.08 x 10^-5Ф₀/√Hz at frequencies above 100Hz, increasing to 1.1 x10^-4Ф₀/√Hz below 1 Hz. The corresponding magnetic field and energy resolution were 270 fT/√Hz and 3.68x10^-29J / Hz respectively, above 100 Hz, and increasing to 710 fT/√Hz and 1.8 x10^-28 J/Hz over a signal frequency range to below 1 Hz.