Quantum and Thermal Creep of Skyrmions and Superconducting Vortices

非技术摘要：涡旋是拓扑激励，出现在许多不同的系统。在超导体中，涡流由围绕非超导芯循环的超电流组成，并且通常是不需要的，因为它们的运动引起耗散，这通常限制了电力、磁体、传感和计算应用中的超导导线和设备的性能。 相反，在某些磁性材料中，被称为skyrmions（磁矩的绕组配置）的涡旋状激发形成，预计将有利于用作下一代低能自旋电子器件中的信息载体。为了减轻超导涡旋的有害影响，并在磁存储器和逻辑的自旋电子器件中利用skyrmions，需要对涡旋，材料无序和热能之间复杂的相互作用进行微观理解。在这项工作中，研究小组正在通过比较包含不同数量无序的材料中的涡旋和skyrmion运动的速率来研究这种相互作用。 该研究为研究生和本科生提供低温测量技术，材料生长和微观分析以及量子材料物理学方面的培训，这些都是包括电力，传感和计算在内的多个行业的必要技能。此外，首席研究员是通过组织一个年度的开放日，在科罗拉多州中部的家庭将被邀请到科罗拉多州矿业学院的实验室图尔斯，科学演示，和动手activities.Technical摘要：涡旋与材料无序的相互作用是许多系统的电子和磁性的主要决定因素。在II型超导体中，涡旋是暴露于磁场时穿透材料的磁通线。在手性磁体和磁性多层膜中，由于晶格键上的磁矩之间的反对称、各向异性交换耦合，可以形成称为skyrmions（磁矩的缠绕配置）的涡旋状激发。虽然超导体中的涡旋和磁系统中的skyrmions的起源是根本不同的，但它们的动力学之间存在惊人的相似之处。例如，两者都可以被建模为与猝灭无序相互作用的颗粒状激发，经历无序介导的集体相互作用并表现出玻璃纸。材料无序使涡旋和skyrmions固定不动，它们的运动可以由足够高的电流或热能引起（热蠕变），或者通过量子隧穿穿过无序定义的能量势垒（量子蠕变）发生。 尽管以前对超导体涡旋动力学进行了大量的研究，但涡旋物理学仍然存在严重的空白。蠕变率是不可预测的，没有分析表达式存在，广泛地捕捉温度和场的蠕变依赖性。本工作的目的是了解超导涡旋的量子蠕变和skyrmions的量子和热蠕变。为此，研究小组利用磁化和传输测量在一定温度和磁场范围内捕获许多超导和磁性材料的蠕变率。随后比较不同材料的蠕变速率与不同的无序景观，使他们能够绘制蠕变和基本材料参数之间的普遍相关性。这项研究可以填补理解涡旋如何克服不同能量障碍的主要空白，并使超导体中的缺陷景观的有效设计成为许多应用和基于skyrmion的自旋电子学的磁性设备。该奖项反映了NSF的法定使命，并被认为值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估来支持。

Non-technical Abstract: Vortices are topological excitations that appear in many different systems. In superconductors, vortices consist of supercurrents circulating around a non-superconducting core and are typically unwanted because their motion induces dissipation that often limits the performance of superconducting wires and devices in power, magnet, sensing, and computing applications. On the contrary, in certain magnetic materials, vortex-like excitations called skyrmions (winding configurations of magnetic moments) form which are predicted to be beneficial for use as information carriers in next-generation low-energy spintronic devices. Mitigating the deleterious effects of superconducting vortices and exploiting skyrmions in spintronic devices for magnetic memory and logic require a microscopic understanding of the complex interplay between vortices, material disorder, and thermal energy. In this work, the research team is investigating this interplay by comparing the rates of vortex and skyrmion motion in materials containing varying amounts of disorder. This research provides training for graduate and undergraduate students in low temperature measurement techniques, materials growth and microanalysis, and quantum materials physics, necessary skillsets in multiple industries including power, sensing, and computing. Additionally, the principal investigator is reaching out to the local community by organizing an annual Open House Community Day for which families in central Colorado will be invited to the Colorado School of Mines for lab tours, science demonstrations, and hands-on activities.Technical Abstract: The interaction of vortices with material disorder is a primary determinant of the electronic and magnetic properties of many systems. In type-II superconductors, vortices are magnetic flux lines that penetrate into the material upon exposure to magnetic fields. In chiral magnets and magnetic multilayers, vortex-like excitations called skyrmions (winding configurations of magnetic moments) can form due to antisymmetric, anisotropic exchange coupling between magnetic moments on lattice bonds. Though the origins of vortices in superconductors and skyrmions in magnetic systems are fundamentally different, striking similarities exist between their dynamics. For example, both can be modeled as particle-like excitations interacting with quench disorder, undergo disorder mediated collective interactions and exhibit glassines. Material disorder immobilizes vortices and skyrmions, whose motion can be induced by sufficiently high currents or thermal energy (thermal creep), or occur via quantum tunneling through disorder-defined energy barriers (quantum creep). Despite considerable previous research on superconductor vortex dynamics, serious gaps still exist in vortex physics. Creep rates are not predictable and no analytic expression exists that broadly captures the temperature and field dependence of creep. The objective of this work is to understand quantum creep of superconducting vortices and both quantum and thermal creep of skyrmions. To this end, the research team captures creep rates in many superconducting and magnetic materials in a range of temperatures and magnetic fields using magnetization and transport measurements. Subsequent comparisons of creep rates in disparate materials with varied disorder landscapes enables them to draw universal correlations between creep and fundamental material parameters. This research could fill a major gap in the understanding of how vortices overcome different energy barriers and enable efficacious design of defect landscapes in superconductors for many applications and magnetic devices for skyrmion-based spintronics.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.