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首页> 外文期刊>Physical review >Thermal fluctuations and flux-tunable barrier in proximity Josephson junctions
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Thermal fluctuations and flux-tunable barrier in proximity Josephson junctions

机译：邻近约瑟夫森结的热涨落和通量可调屏障

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The effect of thermal fluctuations in Josephson junctions is usually analyzed using the Ambegaokar-Halperin (AH) theory in the context of thermal activation. "Enhanced" fluctuations, demonstrated by broadening of current-voltage characteristics, have previously been found for proximity Josephson junctions. Here we report measurements of micrometer-scale normal metal loops contacted with thin superconducting electrodes, where the unconventional loop geometry enables tuning of the junction barrier with applied flux. We observe stronger "enhanced" fluctuations when the flux threading the normal metal loop is near an odd half-integer flux quantum, and for devices with thinner superconducting electrodes. These findings suggest that the activation barrier, which is the Josephson coupling energy of the proximity junction, is different from that for conventional macroscopic Josephson junctions. Simple one-dimensional quasiclassical theory is used to predict the interference effect due to the loop structure, but the exact magnitude of the coupling energy cannot be computed without taking into account the details of the sample dimensions. In this sense, the physics of nanoscale proximity junctions can be related to the thermally activated phase slips (TAPS) model for thin superconducting wires, and indeed our data can be better fitted with the TAPS model than with the AH theory. Besides shedding light on thermal fluctuations in proximity junctions, the findings here also demonstrate a different type of superconducting interference device with two normal branches sharing the same superconducting-normal interface on both sides of the device, which has technical advantages for making symmetrical interference devices.
机译：通常在热激活的情况下，使用Ambegaokar-Halperin（AH）理论分析约瑟夫森结中热涨落的影响。先前已发现邻近约瑟夫森结的“增强”波动，表现为电流-电压特性的扩展。在这里，我们报告了与超导薄电极接触的微米级普通金属环的测量结果，其中非常规的环几何形状可以通过施加的通量来调节结势垒。当穿过普通金属环的通量接近奇数半整数通量量子时，对于超导电极更薄的器件，我们观察到更强的“增强”波动。这些发现表明，激活势垒是邻近结的约瑟夫森耦合能，它不同于常规的宏观约瑟夫森结。简单的一维准经典理论可用于预测由于环路结构引起的干扰效应，但是如果不考虑样本尺寸的细节，就无法计算出耦合能量的确切大小。从这个意义上讲，纳米级接近结的物理性质可以与超细导线的热激活相滑（TAPS）模型相关，实际上，与AH理论相比，TAPS模型可以更好地拟合我们的数据。除了揭示邻近结的热波动之外，这里的发现还证明了另一种类型的超导干扰设备，其两个法向分支在设备的两侧共享相同的超导-法向接口，这在制造对称干扰设备方面具有技术优势。

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