Domain Dynamics and Ultrafast Switching in Magnetic Weyl Semimetals

根据电子材料的导电性，它们通常被称为金属或绝缘体。介于两者之间的是半导体，纯净时是绝缘的，但掺杂电或化学物质时是导电的。研究人员发现了全新的材料类别，“拓扑材料”，挑战了这种既定的范式。该项目支持磁性拓扑金属的实验研究和教育，这些材料具有独特的性能和在先进技术中使用的潜力。例如，磁性拓扑金属具有指向不同方向的虚拟磁场，从而拥有不同的记忆状态。这种状态可以以比千兆赫频率更快的速度切换，并且可以用作新型存储逻辑的基础。研究人员将利用光来研究磁性拓扑金属随时间和位置的特性，以及控制状态之间的超快切换。该项目将有助于建立对这些材料的基本理解，并有可能使它们在未来的纳米电子学和量子计算中得到实际应用。该项目促进的教育工作包括向STEM学生和公众介绍量子材料的新推广方法。第一代大学生将参与其中，让他们对量子材料的现代研究有一个感觉。Weyl半金属的发现是拓扑材料的一个突破，因为不像量子霍尔效应和拓扑绝缘体需要体隙来保护它们的新特性，Weyl半金属不需要。自从磁性Weyl半金属如Co3Sn2S2的发现以来，它们的表征仅限于表面敏感的能带结构测量和输运测量。Berry曲率（动量空间中的磁场）如何在这些拓扑半金属中表现出来，以及畴结构的影响，它们的时间动力学和超快开关，仍然是关键和仍然有待解决的问题。在这个为期三年的项目中，研究小组使用扫描和时间分辨磁光克尔效应显微镜和磁太赫兹光谱学来研究磁Weyl半金属中的畴演变、Berry曲率效应及其动力学。首席研究员的目标是建立这些技术作为一个新的平台来研究磁性拓扑材料，这些材料在该领域不断出现。该项目将有助于建立对磁性Weyl半金属在实空间和动量空间以及它们的时间动力学的各个方面的全面基本理解，以便将它们建立为拓扑自旋电子学和信息处理的新平台。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 SUMMARYElectronic materials are traditionally characterized as metals or insulators based upon their ability to conduct electricity. Lying between these are semiconductors, insulating when pure but conductive when electrically or chemically doped. Researchers have uncovered whole new classes of materials, "topological materials," that defy this established paradigm. This project supports experimental research and education in magnetic topological metals, materials with unique properties and potential for use in advanced technologies. For example, magnetic topological metals host different memory states with a fictitious magnetic field pointing in different directions. Such states can be switched at fast than GHz frequencies and could be used as the basis for a new type of memory logic. The investigators will use light to study the properties of magnetic topological metals as a function of time and position, and control ultrafast switching between states. This project will help to establish a fundamental understanding of these materials and potentially enable their practical use in future nanoelectronics and quantum computing. Educational work fostered by this project includes new outreach methods that will introduce quantum materials to STEM students and the general public. First-generation college students will be involved to give them a sense of modern research in quantum materials.TECHNICAL SUMMARYThe discovery of Weyl semimetals is a breakthrough in topological materials because unlike the quantum Hall effect and topological insulators which need a bulk gap to protect their novel properties, Weyl semimetals do not. Since the discoveries of magnetic Weyl semimetals such as Co3Sn2S2, their characterization has been limited to surface-sensitive band structure measurements and transport measurements. How the Berry curvature (magnetic field in the momentum space) manifest in these topological semimetals, as well as the effects of domain structures, their temporal dynamics and ultrafast switching, remain critical and still-wide-open questions. In this three-year project, the research team uses scanning and time-resolved magneto-optical Kerr effect microscopy and magneto-terahertz spectroscopy to study the domain evolution, the Berry curvature effect, and its dynamics in magnetic Weyl semimetals. The principal investigator aims to establish these techniques as a new platform to study magnetic topological materials that have been constantly emerging in the field. This project will help to establish the comprehensive fundamental understanding of various aspects of magnetic Weyl semimetals in both the real and momentum space and also their temporal dynamics in order to establish them as new platforms for topological spintronics and information processing.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.