Spin Waves in Disordered Potentials: Interplay between Disorder, Nonlinearity, and Incoherence

波理论是物理学的基础，是从雷达到光纤到手机通信的一切基础。波发生在磁性材料中，其中磁自旋以波的形式进行，传播能量和信息。磁性材料在许多技术环境中都很重要，包括固态硬盘。在完全有序的磁性材料中，波会平滑地传播；然而，真实的材料具有无序和缺陷，导致波的局部化，因此信息或能量被困在材料中的某个位置。本研究旨在了解无序磁性材料中波的局部化的许多悬而未决的问题。具体而言，本文解决了三个主要问题：(1)连贯性重要吗？例如，激光是相干的，自旋波也是相干的。(2)非线性是如何破坏局部化的？非线性意味着整体不是各部分的和。在自旋波中，这种效应的强度是可以控制的，它对局域化的影响是可以探索的。(3)混乱会导致离域吗？真实的材料往往表现出混乱。混沌会允许局域波逃逸吗？为了支持这项研究并培养未来的科学家，该项目为本科生和研究生提供了广泛的培训机会，特别是实验物理和理论物理之间的跨学科交叉培训。通过科罗拉多州立大学的“物理小商店”项目，向科罗拉多州的高中推广，重点关注贫困地区的高中。通过组织科学会议、研讨会和专题讨论会，扩大与更广泛的科学界的联系。技术摘要anderson本地化和aubry - andr<s:1>本地化由于其普遍存在的性质，近年来在许多学科中都引起了相当大的兴趣。理论研究已经产生了许多关于相干和非线性对局域化影响的预测，这些预测具有重要的基础意义，但往往存在争议或争论。该项目的研究不仅解决了目前关于定位的几个争论，而且为一些理论预测提供了第一个实验证明。因此，该项目加深了对无序、非线性和相干之间相互作用的理解。此外，该研究还提高了对磁性薄膜中的自旋波动力学和具有无序缺陷的磁性材料中的阻尼过程的理解。具体地说，研究利用了钇铁石榴石（YIG）薄膜带中的自旋波。自旋波的无序势可通过两种方法得到：(1)在YIG带材表面制造无序凹槽；(2)在YIG带材上沉积弯曲线并使电流通过弯曲线来产生无序局域场变化。考虑了两种类型的无序势：随机势和准周期势。前者用于研究Anderson定位，后者用于研究aubry - andr<s:1>定位。这项研究包括实验和理论两方面的努力。该项目由科罗拉多州立大学吴明忠的研究组和科罗拉多矿业学院林肯·卡尔的理论小组合作完成。鉴于本地化效应的潜在应用前景，新计划具有变革性影响。例如，局域模式内的能量密度可以比入射波的能量密度大几个数量级，这种巨大的场增强在能量收集、存储和转换方面具有潜在的应用。除了在本科到研究生阶段的指导和如上所述的推广外，主要研究人员还共同参与课程开发，重点是将最新的应用和实验演示引入研究生的核心课程中电动力学和经典动力系统。

Non-Technical AbstractWave theory is fundamental to physics, underlying everything from radar to fiber optics to cell phone communications. Waves occur in magnetic materials, where the magnetic spin precesses in a wave pattern, propagating energy and information. Magnetic materials are important in many technological contexts, including solid-state hard drives. In a perfectly ordered magnetic material a wave would propagate smoothly; however, real materials have disorder, imperfections that lead to localization of waves, so that information or energy gets trapped in a certain location in the material. This research seeks to understand many unanswered questions about localization of waves in disordered magnetic materials. In particular, three main questions are addressed: (1) Does coherence matter? Lasers, for example, are coherent, and spin waves can be too. (2) How does nonlinearity destroy localization? Nonlinearity means the whole is not the sum of the parts. In spin waves the strength of this effect can be controlled, and its impact on localization explored. (3) Can chaos cause delocalization? Real materials often exhibit chaos. Does chaos allow a localized wave to escape? To support this research and create tomorrow's scientists, the project provides extensive training opportunities for students at undergraduate and graduate levels, especially interdisciplinary cross-training between experimental and theoretical physics. Outreach to high schools in Colorado is accomplished through the Colorado State University "Little Shop of Physics" program, focusing on those in disadvantaged areas. Outreach to the broader scientific community occurs via organizing of scientific conferences, workshops, and symposia.Technical AbstractAnderson localization and Aubry-André localization have both attracted rather considerable interest across a number of disciplines in recent years due to their ubiquitous nature. Theoretical studies have yielded many predictions about the effects of coherence and nonlinearity on localization that are of great fundamental importance but are often controversial or debatable. The research in this project not only settles several current debates on localization, but also provides first experimental justifications to a number of theoretical predictions. As such, the project deepens the understanding of the interplay between disorder, nonlinearity, and coherence in general. Furthermore, the research enhances the understanding of spin-wave dynamics in magnetic thin films and damping processes in magnetic materials with disordered defects. Specifically, the studies make use of spin waves in yttrium iron garnet (YIG) thin film strips. Disordered potentials for spin waves are developed by two approaches: (1) the fabrication of disordered grooves on the surfaces of YIG strips and (2) the development of disordered local field variations by depositing meander lines on the YIG strips and passing electric currents through the lines. Two types of disordered potentials are considered: random potentials and quasi-periodic potentials. The former is used to study Anderson localization, while the latter is used for the study of Aubry-André localization. The research consists of both experimental and theoretical efforts. It is carried out through integral collaborations between Mingzhong Wu's experimental group at Colorado State University and Lincoln Carr's theoretical group at Colorado School of Mines. The new program has transformative impacts in view of promising potential applications of localization effects. For example, the energy density within a localized mode can be several orders of magnitude larger than that of the incident wave, and this huge field enhancement has potential applications for energy harvest, storage, and conversion. In addition to mentorship at undergraduate to graduate levels and outreach as described above, the principal investigators are jointly engaged in curriculum development, focusing on bringing up-to-date applications and experimental demonstrations into graduate core courses in electrodynamics and classical dynamical systems.