Simple model for plastic dynamics of a disordered flux-line lattice
Simple model for plastic dynamics of a disordered flux-line lattice
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无序磁通线晶格塑性动力学的简单模型
DOI：
10.1103/physrevb.64.224517
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发表时间：
2000
影响因子：
3.7
通讯作者：
E. Altshuler
中科院分区：
文献类型：
--
作者：
K. Bassler;M. Paczuski;E. Altshuler
我们使用通过随机钉扎电势驱动的超导涡流的粗粒度模型来研究具有钉扎的 II 型超导体中磁通流的非线性电流电压 $(I\ensuremath{-}V)$ 特性。在实验中，$I\ensuremath{-}V$ 关系测量通量密度梯度下的通量。这里介绍的工作明确地处理了这个关键特征。随着涡流斥力减弱，对于相同的钉扎电势，涡流堆保持全局更陡的斜率，对应于更大的临界电流。此外，当电阻峰值转向更高的电流时，微分电阻的峰值幅度会下降。该模型还表现出所谓的“I\ensuremath{-}V$ 指纹”以及高电流下与欧姆（线性）行为的交叉。因此，许多实验观察到的与软通量线系统塑性流动相关的特性在零温度模型的数值模拟中得到了再现。该模型描述了伦敦长度 (\ensuremath{\lambda}) 尺度上通量线系统的二维切片。它不包括比 \ensuremath{\lambda} 小得多的尺度上的任何自由度，这是指定通量线晶格中的无序程度所必需的。相反，非线性输运行为与沿着涡堆斜坡向下的涡河流的自组织、大规模形态有关。这些形态包括孤立的丝状通道，它们可以在更高的流速下合并形成辫状河，并最终在更高的流速下产生均匀的流动。丝状结构与具有凹曲率或正曲率的 $I\ensuremath{-}V$ 特征相关。辫状河与微分阻力的峰值相关，其中$I\ensuremath{-}V$关系的曲率变为凸形。当辫状河无法吸收更高水平的水流时，就会发生向欧姆行为的转变。我们提出，这些沿着通量梯度流动的自组织形态控制着各种塑性流动行为，包括在随机钉扎的 II 型超导体中观察到的非线性 $I\ensuremath{-}V$ 特性。
We use a coarse-grained model of superconducting vortices driven through a random pinning potential to study the nonlinear current-voltage $(I\ensuremath{-}V)$ characteristics of flux flow in type-II superconductors with pinning. In experiments, the $I\ensuremath{-}V$ relation measures flux flow down a flux density gradient. The work presented here treats this key feature explicitly. As the vortex repulsion weakens, the vortex pile maintains a globally steeper slope, corresponding to a larger critical current, for the same pinning potential. In addition, the magnitude of the peak in the differential resistance falls as the resistance peak shifts to higher currents. The model also exhibits so-called $``I\ensuremath{-}V$ fingerprints'' and crossover to Ohmic (linear) behavior at high currents. Thus, many of the experimentally observed characteristics associated with the plastic flow of soft flux-line systems are reproduced in numerical simulations of the zero-temperature model. This model describes a two-dimensional slice of the flux-line system at the scale of the London length (\ensuremath{\lambda}). It does not include any degrees of freedom at scales much smaller than \ensuremath{\lambda}, which are required to specify the degree of disorder in a flux-line lattice. Instead, the nonlinear transport behaviors are related to the self-organized, large-scale morphologies of the vortex river flow down the slope of the vortex pile. These morphologies include isolated filamentary channels, which can merge at higher flow rates to make a braided river and eventually give uniform flow at even higher flow rates. The filamentary structure is associated with an $I\ensuremath{-}V$ characteristic that has concave, or positive, curvature. The braided river is associated with the peak in the differential resistance, where the curvature of the $I\ensuremath{-}V$ relation changes to convex. The transition to Ohmic behavior comes about as the braided river floods when it cannot absorb a higher level of flow. We propose that these self-organized morphologies of flux flow down a flux gradient govern the various plastic flow behaviors, including nonlinear $I\ensuremath{-}V$ characteristics, observed in type-II superconductors with random pinning.