Effective area in slotted high Tc dc washer superconducting quantum interference devices

Slotted high $T_c$ dc washer superconducting quantum interference devices (SQUIDs) exhibit increased effective areas with respect to their solid washer counterparts. To investigate this systematically, a series of SQUIDs with zero to eight slots is fabricated. A maximum gain in effective area of 24% was observed for four slots. A model, considering the slotted washer as a parallel circuit of pick-up inductances can account for the enhanced effective area. A good fit with the experiments is obtained if the London penetration depth at 0 K is taken to be 267 nm. Furthermore, the model provides the current distribution in the slotted SQUIDs.