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

波动理论是物理学的基础，是从雷达到光纤到手机通信的基础。 波发生在磁性材料中，其中磁自旋以波模式进动，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。 在完美有序的磁性材料中，波会平滑地传播;然而，真实的材料具有无序性，导致波局部化的缺陷，因此信息或能量被困在材料中的某个位置。 这项研究旨在了解许多悬而未决的问题，在无序磁性材料中的波的本地化。 特别是，三个主要问题得到解决：（1）是否一致的问题？ 例如，激光是相干的，自旋波也可以是。 (2)非线性如何破坏局部化？ 非线性意味着整体不是部分之和。 在自旋波中，这种效应的强度是可以控制的，并探讨了它对局域化的影响。 (3)混沌能导致非定域化吗？ 真实的材料经常表现出混乱。 混沌允许局部波逃逸吗？ 为了支持这项研究并创造明天的科学家，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”方案，向科罗拉多州的高中进行宣传，重点是贫困地区的高中。 通过组织科学会议、研讨会和专题讨论会，向更广泛的科学界进行推广。技术摘要安德森本地化和奥布里-安德烈本地化由于其无处不在的性质，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性和非线性对局域化的影响的预测，这些预测具有非常重要的基本意义，但往往是有争议的或有争议的。 该项目的研究不仅解决了当前关于本地化的几个争论，而且还为一些理论预测提供了第一个实验依据。 因此，该项目加深了对无序，非线性和连贯性之间相互作用的理解。 此外，该研究增强了对磁性薄膜中自旋波动力学和具有无序缺陷的磁性材料中阻尼过程的理解。 具体而言，研究利用自旋波在钇铁石榴石（YIG）薄膜带。 自旋波的无序势可以通过两种方法产生：（1）在YIG条表面制造无序沟槽;（2）在YIG条上沉积曲折线并通过电流来产生无序局域场变化。 两种类型的无序势被认为是：随机势和准周期势。 前者用于研究安德森局域化，后者用于研究Aubry-André局域化。该研究包括实验和理论两方面的努力。 它是通过科罗拉多州立大学吴明忠实验组和科罗拉多矿业学院林肯·卡尔理论组的整体合作进行的。 鉴于本地化效应的潜在应用前景，新计划具有变革性的影响。 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，并且这种巨大的场增强具有用于能量收集、存储和转换的潜在应用。 除了在本科生到研究生水平和如上所述的推广导师，主要研究人员共同参与课程开发，重点是把最新的应用和实验演示到电动力学和经典动力系统的研究生核心课程。

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.