ジョセフソン素子用Pb合金超伝導薄膜の磁束トラップ特性

概要

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Magnetic-flux trapping in Pb-alloy thin films is studied experimentally. In order to clarify pinning characteristics of thin films, which dominate flux trapping, trapped flux in Pb-alloy thin films is measured in-situ from the increment of the quasiparticle current of the Josephson junction made of these Pb-alloy thin films. Experimental results are discussed with the critical state model based on the pinning theory of superconductors. From the material dependence of flux trapping, it is shown that the addition of Au to Pb increases flux trapping due to the occurence of strong pinning centers of normal precipitates of AuPb<SUB>2</SUB> and AuPb<SUB>3</SUB> etc. It is also shown that the addition of Bi decreases flux trapping due to the large value of the London penetration depth of PbBi films. From the temperature dependence of flux trapping, it is shown that the amount of the trapped flux is reduced by raising the temperature of thin films. Finally, the effect of the trapped flux in junction electrodes on the suppression of the critical current of the junction is discussed quantitatively.
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