Self-Organized Dynamics of Superconducting Flux

该奖项支持基础凝聚态物理的理论研究。颗粒状物体在无序介质中的集体迁移通常是间歇性的，由雪崩控制。雪崩可以很小，也可以是系统范围的，或者它们可以表现出缩放行为。了解雪崩动力学对于包括河流水文学、超导性、太阳耀斑和互联网流量在内的各种学科具有基础理论和技术重要性。理解雪崩动力学的许多理论努力都集中在细胞“沙堆”模型的行为上。细胞模型提供了一种粗粒度的物理描述，自然地结合了对象的粒度和分解过程的阈值性质。它们通常还具有数值上易于处理的优点，使得在一定长度和时间尺度范围内研究它们的行为成为可能，这需要检测缩放的存在与否，并确定动力学的普遍特征。离散的细胞模型将用于研究II型超导体驱动的磁涡流的非线性输运特性，并与实验建立可量化的联系。有人提出，由于涡旋之间的排斥相互作用，以及涡旋与晶格缺陷或杂质之间的吸引钉住，超导体中量子化涡旋的动力学类似于一堆沙子中的颗粒。此外，在大多数实验中，涡的过阻尼运动被大多数沙堆型细胞模型的阈值动力学捕获。因此，磁涡旋的驱动动力学是一个理想的物理系统，可以尝试用细胞模型来模拟。此外，一些表征涡旋动力学的实验为建立和探索细胞模型与超导涡旋大尺度行为之间的联系提供了机会。通过建立这种联系，其他各种非平衡系统动力学的普遍方面也可能得到更好的理解。这项研究建立在现有的研究结果的基础上，该研究已经建立了一个漩涡动力学的细胞模型，并证明它至少捕获了一些大规模的特性，包括一些实验观察到的超导体非线性输运的定量结果。在新的工作中，大规模的数值模拟将通过扩展我们现有的模型来研究II型超导体中观察到的各种新现象，从而进一步探索细胞模型和超导涡流的普遍动力学之间的联系。特别是，现有的模型将被扩展到考虑涡运动的电阻加热引起的热效应，并描述涡的三维性质。研究提出了模拟实验，以测量通量穿透的缩放特性，包括树突的形成，以及电压噪声和涡流的分布。此外，还提出了探索元胞模型的普遍动力学和涡旋动力学与其他物理系统的关系的研究。将采用新颖的数值算法来实现模型的大规模并行模拟。还计划与实验小组合作。研究生将参与该项目，研究将加强将计算纳入研究生物理课程的努力。将建立一个互动网站，以促进外联活动。讲座将在当地的高中举行。该基金支持基础凝聚态物理。这项研究主要使用计算方法来研究超导体中磁涡流的输运。从基本的和应用的两个方面来看，这个问题都是令人感兴趣的。理论方法利用了这一问题与砂堆中砂粒运动问题之间的联系。作为这个项目的一部分，我们计划了一个强有力的教育和推广计划

This award supports theoretical research on fundamental condensed matter physics. The collective transport of granular objects driven through a disordered medium is often intermittent, governed by avalanches. The avalanches can be small, or system-wide, or they can exhibit scaling behavior. Understanding avalanche dynamics is of fundamental theoretical and technological importance to a variety of subjects including river hydrology, superconductivity, solar flares, and Internet traffic. Much of the theoretical effort to understand avalanche dynamics has focused on the behavior of cellular "sandpile" models. Cellular models provide a coarse-grained physical description that naturally incorporates both the granularity of the objects and the threshold nature of the breakdown process. They also often have the benefit of being numerically tractable, making it possible to study their behavior over a range of length and time scales, which is needed to detect the presence or absence of scaling, and to determine the universal features of the dynamics. Discrete, cellular models will be used to study the nonlinear transport properties of magnetic vortices driven through a type II superconductor, and to make quantifiable connection with experiments. It has been suggested that, because of the repulsive interactions between vortices, and the attractive pinning between vortices and lattice defects or impurities, the dynamics of quantized vortices in a superconductor is analogous to that of grains in a pile of sand. Additionally, the over-damped motion of vortices in most experiments is captured by the threshold dynamics of most sandpile type cellular models. Therefore, the driven dynamics of magnetic vortices is an ideal physical system to attempt to model with cellular models. Furthermore, a number of experiments characterizing vortex dynamics present opportunities for establishing and exploring the connection between cellular models and the large-scale behavior of superconducting vortices. By establishing that connection, the universal aspects of the dynamics of a variety of other nonequilibrium systems may also become better understood.This research builds on existing results that have developed a cellular model for vortex dynamics, and demonstrated that it captures at least some of the large-scale properties, including some quantitative results, of the nonlinear transport in superconductors that are observed experimentally. In the new work, large-scale numerical simulations will be used to further explore the connection between the universal dynamics of cellular models and of superconducting vortices by extending our existing model to study a variety of novel phenomena observed in type II superconductors. In particular, the existing model will be extended to account for thermal effects caused by the resistive heating of vortex motion, and to describe the three-dimensional nature of vortices. Studies are proposed to model experiments that measure the scaling properties of flux penetration, including the formation of dendrites, and of distributions of voltage noise and vortex flow. Additionally, studies exploring the relationship of the universal dynamics of the cellular model, and of vortex dynamics, to other physical systems are proposed. Novel numerical algorithms will be employed to achieve massively parallel simulations of the models. Collaborations with experimental groups are also planned.Graduate students will be involved in the project and the research will enhance efforts to incorporate computation into the graduate physics curriculum. An interactive website will be developed to promote outreach. Talks will be given at local high schools. %%%This grant supports fundamental condensed matter physics. The research investigates, primarily using computational methods, the transport of magnetic vortices in superconductors. This problem is of interest for both basic and applied reasons. The theoretical approach utilizes the connection between this problem and that of the motions of grains of sand in a sandpile. A strong educational and outreach program is planned as part of this project.***