Directly coupled slotted high-Tc dc SQUIDs

A flux quantization model gives estimates for the effective area and washer inductance of slotted high-Tc dc SQUIDs. The inductance prediction has not been verified yet. Here, the theoretical dependence of washer inductance and effective area for four slotted SQUID types on the London penetration depth λ is presented. We implemented the SQUIDs in a directly coupled configuration. Electrical properties such as transfer function and flux noise are determined and compared to literature values with reasonable success. For all magnetometers, effective area measurements show the expected proportionality on the inductance for λ=400 nm at 77 K. Also, the directly measured inductance, measured after separating the SQUIDs from the pick-up loop, shows excellent agreement with the model. The effective areas of these autonomous SQUIDs are 40% higher than predicted, most probably due to flux focusing by the superconducting surroundings.