Complex inductance, excess noise, and surface magnetism in dc SQUIDs.
We have characterized the complex inductance of dc SQUIDs cooled to millikelvin temperatures. The SQUID inductance displays a rich, history-dependent structure as a function of temperature, with fluctuations of order 1 fH. At a fixed temperature, the SQUID inductance fluctuates with a 1/f power spectrum; the inductance noise is highly correlated with the conventional 1/f flux noise. The data are interpreted in terms of the reconfiguration of clusters of surface spins, with correlated fluctuations of effective magnetic moments and relaxation times.
Department of Physics, University of Wisconsin, Madison, Wisconsin 53706, USA.
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Sendelbach
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Hover
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Mück
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McDermott