高温超导约瑟夫森结电学参数不确定度评定

    Uncertainty Evaluation of Electrical Parameters of High-Temperature Superconductor Josephson Junctions

    • 摘要: 高温超导量子电压标准可在液氮温区工作,有利于量子电压标准的大规模推广使用。约瑟夫森电压正比于驱动微波的频率,而微波频率应当与结的特征频率匹配,因此需要准确评估结的正常态电阻和临界电流来确定结的特征频率。在LSAT衬底上制备出高温超导约瑟夫森双晶结(HTS JJ),采用四端法测量高温超导约瑟夫森结I-V特性曲线,通过分析I-V曲线特性来获取LSAT双晶结的正常态电阻及临界电流。高温超导约瑟夫森结I-V特性中存在噪声圆化和自热效应两种畸变,导致正常态电阻与本征临界电流值变化。为在这两种畸变存在的情况下仍能准确估计出HTS JJ电学参数,采用几何平均准则与RSJ模型组合的方法,对正常态电阻及本征临界电流值进行估计,并评定其不确定度。实验及评定结果表明,LSAT衬底上的4 µm双晶结为SNS结且符合RSJ模型,正常态电阻值为0.06397 Ω,合成相对标准不确定度为6.1%;本征临界电流为3.3214 mA,合成相对标准不确定度为6.0%。该工作将为研制实用化高温超导量子电压标准装置提供支撑。

       

      Abstract: High-temperature superconductor quantum voltage standard operates at liquid nitrogen temperature, which is favorable for wide-spread application of quantum voltage standard. Josephson voltage is proportional to the applied microwave frequency, which should be matched to the eigen-frequency of the junction. Therefore, the normal state resistance and critical current of the junction should be accurately evaluated to obtain its eigen-frequency. High-temperature superconductor bicrystal Josephson junctions are fabricated on LSAT substrates, and 4-probe method is used to measure their I-V characteristic curves, from which the normal-state resistance and the critical current are extracted. Due to thermal-noise rounding effect and self-heating, the I-V characteristics of high-temperature superconductor Josephson junctions are usually distorted, thus the normal-state resistance and intrinsic critical current values are varied. In this work, geometric-mean criterion and RSJ model are combined for proper evaluation of both parameters and their uncertainty level. Experimental results show that the 4-µm bicrystal junctions on LSAT substrates is a SNS junction and conforms to the RSJ model, with a normal-state resistance value of 0.06397 Ω and a synthetic relative standard uncertainty of 6.1%. The intrinsic critical current is 3.3214 mA with a synthesize relative standard uncertainty of 6.0%. This work will support the development of a practical high-temperature superconducting quantum voltage standard device.

       

    /

    返回文章
    返回