Quantum and Thermal Creep of Skyrmions and Superconducting Vortices

非技术摘要：涡旋是出现在许多不同系统中的拓扑激励。在超导体中，涡旋由绕着非超导核心循环的超导电流组成，通常是不受欢迎的，因为它们的运动会引起损耗，这往往会限制超导导线和设备在电力、磁体、传感和计算应用中的性能。相反，在某些磁性材料中，被称为Skyrmions(磁矩缠绕构型)的涡旋状激发形式被预测为有利于在下一代低能量自旋电子器件中用作信息载体。为了减轻超导涡旋的有害影响，并利用自旋电子器件中的Skyrmion来实现磁记忆和逻辑，需要从微观上理解涡旋、材料无序和热能之间的复杂相互作用。在这项工作中，研究小组正在通过比较包含不同无序程度的材料中的涡旋和天米子运动的速度来研究这种相互作用。这项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方面的培训，这些都是电力、传感和计算等多个行业的必要技能。此外，首席研究人员正在通过组织一年一度的开放参观社区日来接触当地社区，科罗拉多州中部的家庭将被邀请到科罗拉多矿业学校进行实验室参观、科学演示和动手活动。技术摘要：漩涡与物质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。在第二类超导体中，涡旋是暴露在磁场中时渗透到材料中的磁通线。在手性磁体和磁性多层膜中，由于晶格键上的磁矩之间反对称的各向异性交换耦合，可以形成被称为Skyrmions(磁矩的缠绕构型)的涡旋状激发。尽管超导体中的涡旋和磁系统中的天子的起源从根本上不同，但它们的动力学存在惊人的相似之处。例如，两者都可以被模拟为与猝灭无序相互作用的粒子状激发，经历无序介导的集体相互作用，并展示玻璃。材料无序使涡旋和天子不动，它们的运动可以由足够大的电流或热能诱导(热蠕变)，或通过量子隧道穿过无序定义的能垒(量子蠕变)发生。尽管前人对超导体涡旋动力学进行了大量的研究，但在涡旋物理方面仍然存在着严重的空白。蠕变速率是不可预测的，并且不存在广泛地捕捉蠕变的温度和场相关性的解析表达式。这项工作的目的是了解超导涡旋的量子蠕变以及Skyrmions的量子蠕变和热蠕变。为此，研究小组利用磁化和传输测量，在一定的温度和磁场范围内捕获了许多超导和磁性材料的蠕变速率。随后对具有不同无序状态的不同材料的蠕变速率进行比较，使他们能够得出蠕变和基本材料参数之间的普遍关联。这项研究可以填补在了解涡旋如何克服不同的能量障碍并使有效设计用于许多应用的超导体和用于基于天空的自旋的磁性设备中的缺陷景观方面的一个重大空白。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

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.