Magnetization manipulation and antiferromagnetic dynamics driven by spin current in Weyl semimetals

非技术摘要：控制固态材料中的磁性是日常生活中广泛使用的许多设备运行的关键。这些设备的应用包括计算机中的数据存储、信用卡上的数据加密和高频信号产生，仅举几例。传统上，磁状态的控制是通过使用外部施加的磁场来获得的，但这限制了这些设备的物理占地面积和操作速度。然而，通过利用电场或充电电流等其他手段来控制铁磁和反铁磁材料中的磁性状态，可以克服这些限制，并有可能实现更先进的纳米级器件，以极高的速度产生、传输和处理信号。然而，对铁磁和反铁磁材料中磁态的电流诱导控制和自旋动力学的基本认识还处于起步阶段。本项目将研究一种新兴的量子固态材料平台，即Weyl半金属，以演示通过电荷电流对磁态的控制。在这些量子材料中，原子以特殊的构型排列，从而产生独特的性质，这反过来又允许有效地控制铁磁材料的磁态，并在反铁磁材料中诱导自旋动力学。这项研究的成功将为全面理解电荷电流诱导的自旋操纵和磁性材料中的动力学奠定基础，这将对新兴的量子自旋电子学领域产生深远的影响。此外，这项研究项目将为合作的少数族裔服务机构的本科生提供研究经验、培训和积极的指导。将与大匹兹堡地区的初中和高中教师建立联系，以开发物理演示，并就电和磁主题制定详细的教案。技术摘要：利用电场感应的自旋电流对磁序(即铁磁体或反铁磁体的Néel矢量的净磁化)进行能量高效和无场操纵是实现先进的自旋电子学应用的关键，这些应用包括用于产生、传输和检测高频信号的超快磁存储器件、太赫兹振荡器和磁子器件。另一方面，具有较低晶体对称性的拓扑材料，如Weyl半金属，拥有自旋-动量锁定电子态，可以导致有效的电荷到自旋转导，以及大量其他与量子自旋电子学高度相关的新现象。该研究项目将利用基于范德华的Weyl半金属的结晶薄膜，并将它们与各种磁系统耦合，以构建原子锐利的超晶格，用于研究自旋操纵和自旋动力学。这个研究项目的科学目标有两个：(1)获得关于半导体和绝缘铁磁体中磁化强度的无场自旋-轨道扭矩转换的潜在机制的时间分辨和空间分辨的观点。(2)利用Weyl半金属中离面取向的自旋流，研究易平面反铁磁体中自旋电流诱导的Néel矢量动力学和反铁磁体的自旋泵浦。这项研究的目标是展示反铁磁振荡器的工作原理。这一奖项反映了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:Control of the magnetic properties in solid-state materials is key to the operation of many devices that are extensively used in daily life. Applications of such devices include data storage in computers, data encryption on credit cards, and high-frequency signal generation, to name a few. Conventionally, the control of magnetic state is obtained by using an externally applied magnetic field, but this restricts the physical footprint and operational speed of these devices. However, the control of the magnetic state in ferromagnetic and antiferromagnetic materials by other means, such as utilizing electric field or charge current, can overcome these limitations, and potentially realize more advanced nanoscale devices for generating, transmitting, and processing signals at extremely high speeds. However, the fundamental understanding of electric current-induced control and spin dynamics of the magnetic state in ferromagnetic and antiferromagnetic materials is still in its infancy. This project will study an emergent quantum solid-state material platform, namely Weyl semimetals, to demonstrate control of the magnetic state through electric charge current. In these quantum materials, the atoms are arranged in a special configuration that gives rise to unique properties, which in turn allow for an efficient control of magnetic state in ferromagnetic materials and induce spin dynamics in antiferromagnetic materials. The success of this research project will lay the foundation to build a comprehensive understanding of electric charge current-induced spin manipulation and dynamics in magnetic materials, which will have far reaching implications for the emerging field of quantum spintronics. Furthermore, this research project will provide research experience, training, and active mentorship to undergraduate students from a collaborating minority serving institution. Connections with middle school and high school teachers in the greater Pittsburgh area will be established to develop physics demonstrations with detailed lesson plans on the topics of electricity and magnetism. Technical abstract:An energy efficient and field-free manipulation of the magnetic order, i.e., net magnetization of a ferromagnet or Néel vector of an antiferromagnet, using electric field induced spin current is key to realize advanced spintronic applications that include ultra-fast magnetic memory devices, terahertz oscillators, and magnonic devices for generation, transmission, and detection of high-frequency signals. On the other hand, topological materials with lower crystal symmetries, such as Weyl semimetals, host spin-momentum locked electronic states that can lead to an efficient charge to spin transduction and a plethora of other novel phenomena that are highly relevant for quantum spintronics. This research project will utilize crystalline thin films of van der Waals based Weyl semimetals and couple them with a variety of magnetic systems to build atomically sharp superlattices for studying spin manipulation and spin dynamics. The scientific objectives of this research project are two-fold: (1) To obtain a time resolved and spatially resolved view on the underlying mechanisms of field-free spin-orbit torque switching of magnetization in semiconducting and insulating ferromagnets. (2) To study spin-current induced Néel vector dynamics in easy plane antiferromagnets and subsequent spin-pumping from antiferromagnets by exploiting out-of-plane oriented spin current in Weyl semimetals. This research objective is aimed at demonstrating the working principle of an antiferromagnetic oscillator.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.