Monte Carlo simulations of thermal fluctuations in moderately damped Josephson junctions: Multiple escape and retrapping, switching- and return-current distributions, and hysteresis
Monte Carlo simulations of thermal fluctuations in moderately damped Josephson junctions: Multiple escape and retrapping, switching- and return-current distributions, and hysteresis
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DOI：
10.1103/physrevb.78.054526
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发表时间：
2008-07
影响因子：
3.7
通讯作者：
J. C. Fenton;P. Warburton
中科院分区：
文献类型：
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作者：
J. C. Fenton;P. Warburton
在温度T*中，中等阻尼约瑟夫森结的开关电流分布的宽度sigma的温度依赖性中的交叉已经在最近的一些论文中被报道，具有正的d σ /dT和IV特性与较低温度T T*的欠阻尼行为相关。我们通过蒙特卡罗模拟详细研究了温度T*附近约瑟夫森结的行为，包括从运行状态恢复到由Ben-Jacob等人的模型给出的超电流状态。Rev. 26, 2805(1982)]。我们讨论了多重逃逸和重捕获事件在中等阻尼状态下的重要作用，特别是考虑到T附近区域的行为。我们表明，通过考虑两个交叉温度，行为更充分地被理解，分布和sigma(T)的形状在T*周围，以及在较低的T< T*，很大程度上取决于传统的热激活开关分布的形状。我们证明了特征温度T*对于特定的约瑟夫森结不是唯一的，而是与施加偏置电流的斜坡速率有关。我们还考虑了中等阻尼约瑟夫森结的迟滞，并讨论了在减小电流坡道时较少测量的回电流分布。我们发现在T*以上应该会有一些滞回。我们强调了在确定阻尼参数Q时适当考虑热波动的重要性，即使远低于T*。
A crossover at a temperature T* in the temperature dependence of the width sigma of the distribution of switching currents of moderately damped Josephson junctions has been reported in a number of recent papers, with positive d sigma/dT and IV characteristics associated with underdamped behavior for lower temperatures T T*. We have investigated in detail the behavior of Josephson junctions around the temperature T* by using Monte Carlo simulations including retrapping from the running state into the supercurrent state as given by the model of Ben-Jacob et al. [Phys. Rev. A 26, 2805 (1982)]. We develop discussion of the important role of multiple escape and retrapping events in the moderate-damping regime, in particular considering the behavior in the region close to T. We show that the behavior is more fully understood by considering two crossover temperatures and that the shape of the distribution and sigma(T) around T*, as well as at lower T< T*, are largely determined by the shape of the conventional thermally activated switching distribution. We show that the characteristic temperatures T* are not unique for a particular Josephson junction but have some dependence on the ramp rate of the applied bias current. We also consider hysteresis in moderately damped Josephson junctions and discuss the less commonly measured distribution of return currents for a decreasing current ramp. We find that some hysteresis should be expected to persist above T*. We highlight the importance, even well below T*, of accounting properly for thermal fluctuations when determining the damping parameter Q.