Investigation of YBCO SQUIDs with gold damping resistors

It has been previously shown that resistively damping the inductances of YBCO SQUIDs reduces the degradation of their output voltage by large values of the screening parameter. This paper reports on the viability of using gold damping resistors with YBCO dc SQUIDs, connected via in situ gold/YBCO contacts deposited by laser ablation on 24° STO bicrystal substrates. It is shown that for SQUIDs of our design that this technique enhances their normalized voltage modulation, compared to their undamped counterparts at 77 K. The amount of enhancement agrees well with that predicted by Enpuku´s theory. The SQUID behavior was studied over a wide range of values of the effective screening parameter, β_eff, which was achieved by measuring the SQUIDs over a temperature range of 20-77 K. These measurements confirmed that the behavior of this SQUID design is inline with established theory.