Quantum and Thermal Creep of Skyrmions and Superconducting Vortices

摘要：涡旋是一种拓扑激励，存在于许多不同的系统中。在超导体中，涡流是由在非超导磁芯周围循环的超电流组成的，通常是不需要的，因为它们的运动会引起耗散，这通常会限制超导导线和设备在电力、磁铁、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（磁矩的缠绕构型）的涡状激励形成，预计将有利于用作下一代低能自旋电子器件的信息载体。减轻超导涡旋的有害影响和利用自旋电子器件中的磁记忆和逻辑需要对涡旋、材料无序和热能之间复杂的相互作用有一个微观的理解。在这项工作中，研究小组通过比较含有不同无序量的材料中的涡旋和涡激子运动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、量子材料物理等多个行业的必要技能培训，包括电力、传感和计算。此外，首席研究员还通过组织一年一度的开放日社区日来接触当地社区，届时科罗拉多州中部的家庭将被邀请到科罗拉多矿业学院参观实验室、进行科学演示和实践活动。技术摘要：涡旋与材料无序的相互作用是许多系统的电子和磁性能的主要决定因素。在ii型超导体中，涡流是暴露在磁场下穿透材料的磁通量线。在手性磁体和磁性多层体中，由于晶格键上磁矩之间的不对称、各向异性交换耦合，可以形成涡状激励，称为skyrmions（磁矩的缠绕构型）。虽然超导体中的涡旋和磁性系统中的涡旋的起源根本不同，但它们的动力学却存在惊人的相似之处。例如，两者都可以建模为与淬火失序相互作用的类粒子激发，经历失序介导的集体相互作用，并表现出glassines。材料的无序使漩涡和天幕固定不动，它们的运动可以由足够高的电流或热能（热蠕变）引起，或者通过无序定义的能量垒（量子蠕变）通过量子隧道发生。尽管前人在超导体涡旋动力学方面做了大量的研究，但涡旋物理仍然存在严重的空白。蠕变速率是不可预测的，也没有解析表达式可以广泛地反映蠕变对温度和场的依赖。这项工作的目的是了解超导涡旋的量子蠕变和skyrmions的量子蠕变和热蠕变。为此，研究小组通过磁化和输运测量，在一定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。随后对不同材料的蠕变率进行比较，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，并能够有效地设计超导体中的缺陷景观，用于许多应用和基于skyrron的自旋电子学的磁性器件。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值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.