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(a) SQUID washer design; dotted line indicates grain boundary; (b) coupling strength vs radial distance from the slit [numerical calculation for design in (a)]. Inset: Magnetic flux coupled by a single vortex into the SQUID hole; numerical calculation for design in (a) (squares) and for a circular washer (disks); the line is obtained from analytical calculation (Ref. 8) for a circular washer; (c) images of the SQUID washer for two different cooling fields .
rms flux noise of YBCO dc SQUID at showing Lorentzian noise due to a single dominating fluctuator (a) and low-frequency -noise (b). Inset: time trace of the SQUID output with a single dominating fluctuator.
Sum of squared coupling strengths vs number of vortices . Dashed line: homogeneous vortex distribution. Inset: fraction of vortices found at a distance from the slit edge for different cooling fields .
Spectral density of flux noise vs number of vortices . Dashed line: homogeneous vortex distribution. Inset: Average spectral density of radial motion vs , calculated from and .
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