Two-dimensional macroscopic quantum tunneling in multi-gap superconductor Josephson junctions
Two-dimensional macroscopic quantum tunneling in multi-gap superconductor Josephson junctions
复制标题
多间隙超导体约瑟夫森结中的二维宏观量子隧道效应
DOI：
10.1088/1742-6596/568/2/022006
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发表时间：
2014
期刊：
影响因子：
--
通讯作者：
and Masahiko Machida
中科院分区：
文献类型：
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作者：
Hidehiro Asai;Shiro Kawabata;Yukihiro Ota;and Masahiko Machida
超导器件的低温特性为研究不同的超导现象提供了明确的途径。研究了单能隙超导体和双能隙超导体组成的约瑟夫森结中的宏观量子隧穿。由于这种结具有两种超导相位差，计算MQT逃逸率需要在多维位形空间中分析量子隧穿。我们的方法是半经典近似沿着一维曲线在二维势能景观，通过鞍点连接两个相邻的潜在的（本地）最小值。我们发现该系统有两条可能的隧穿路径：同相路径和异相路径，前者由约瑟夫森等离子体频率表征，后者由双带超导体中的特征集体模约瑟夫森-莱格特模的频率表征.依赖于外部偏置电流和带间约瑟夫森耦合能量，其中之一主要有助于MQT。我们的数值计算表明，就MQT逸出率的偏置电流依赖性而言，同相路径和异相路径之间的差异是明显的。这一结果表明，我们的MQT设置是约瑟夫森-莱格特模式的指标。
Low-temperature characters of superconducting devices yield definite probes for different superconducting phenomena. We study the macroscopic quantum tunneling (MQT) in a Josephson junction, composed of a single-gap superconductor and a two-gap superconductor. Since this junction has two kinds to the superconducting phase differences, calculating the MQT escape rate requires the analysis of quantum tunneling in a multi-dimensional configuration space. Our approach is the semi-classical approximation along a 1D curve in a 2D potential-energy landscape, connecting two adjacent potential (local) minimums through a saddle point. We find that this system has two plausible tunneling paths; an in-phase path and an out-of-phase path. The former is characterized by the Josephson-plasma frequency, whereas the latter is by the frequency of the characteristic collective mode in a two-band superconductor, Josephson-Leggett mode. Depending on external bias current and inter-band Josephson-coupling energy, one of them mainly contributes to the MQT. Our numerical calculations show that the difference between the in-phase path and the out-of-phase path is manifest, with respect to the bias-current-dependence of the MQT escape rate. This result suggests that our MQT setting be an indicator of the Josephson-Leggett mode.