Reduction of low-frequency noise in high-T-c SQUIDs by artificial defects

摘要

We demonstrated that (i) quite simple arrangements of a few 'strategically positioned' antidots can lead to significant reduction of the low-frequency noise in high-T-c SQUIDs and (ii) that a careful analysis of the unlocked SQUID signal can be used to identify the number and position of vortices that penetrate the superconducting device. By using only two antidots in the vicinity of the Josephson junction and a ring of antidots at the position of the first penetrating vortices, the onset field at which the low-frequency noise starts to increase is shifted from B-on approximate to 8 muT without antidots to B-on approximate to 40 muT in field-cooled experiments and to B-on approximate to 25 muT in zero-field cooled measurements. The exact position for the antidots is obtained by careful analysis of the impact of the position of moving vortices on the low-frequency noise, the driving forces for vortex motion and the position of the first vortices that penetrate the SQUID washer. The attained improvement of the sensitivity of the superconducting device demonstrates the potential of antidots in applications which not necessarily are restricted to high-T-c SQUIDS. (C) 2002 Elsevier Science B.V. All rights reserved. [References: 30]