Probing Chiral Fermion Dynamics in Topological Semimetals

探索拓扑半金属中的手性费米子动力学

• 批准号: 1809815
• 负责人: Nuh Gedik
• 金额: $ 52.31万
• 依托单位: Massachusetts Institute of Technology
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2018
• 资助国家: 美国
• 起止时间: 2018-06-01 至 2022-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1809815&HistoricalAwards=false
• 关键词: Probing; Chiral; Fermion; Dynamics; Topological

Nontechnical abstract:Topological semimetals have recently emerged as an important frontier of condensed matter physics. In these materials, the crossing points of electronic energy levels are topologically protected. It has been predicted that the electrons around these crossing points should display fascinating unconventional behavior in response to external perturbations such as passing an electrical current or shining light. The goal of this project is to experimentally investigate optical properties of topological semimetals. The realization of novel optical and optoelectronic phenomena in topological semimetals may lead to useful technological applications. Students and postdocs with expertise both in topological physics and time resolved optical techniques will be trained as the next generation of scientists in these fields. A crucial part of the educational component of this program is to contribute to improving the quality of K-12 math and science education especially in socio-economically impacted regions.Technical abstract:Weyl semimetal is a new topological phase of matter predicted to display fascinating properties. While the electronic band structure and transport have been systematically studied using angle resolved photoemission spectroscopy, scanning tunneling microscopy and electrical transport, optical properties of these materials remain largely unexplored despite predictions of many unconventional optical behaviors. The goal of this research program is to investigate the novel optical properties of chiral Weyl fermions in topological semimetals. In particular, it has been predicted that, in the presence of parallel electric and magnetic fields, Weyl fermions with different chiralities should intermix and give rise to a magnetic field dependent conductivity. It has been difficult to conclusively observe this phenomenon, known as the chiral anomaly, solely based on transport measurements. In this project, time-resolved photocurrent microscopy, transient grating spectroscopy and terahertz spectroscopy will be used to optically detect signatures of the chiral anomaly in Weyl semimetals. Additionally, photocurrent response of a Weyl semimetal will be used to map out the quantum geometry of its electronic wavefunction. This will allow detection of the Berry curvature monopoles and dipoles that arise from a Weyl node. The realization of the novel optical and optoelectronic phenomena in topological semimetals may allow us to control the Weyl fermions and their associated quantum anomalies by optical means, leading to useful optical and optoelectronic applications.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.

摘要：近年来，拓扑半金属已成为凝聚态物理的一个重要前沿。在这些材料中，电子能级的交叉点受到拓扑保护。据预测，在这些交叉点周围的电子应该表现出迷人的非常规行为，以响应外部扰动，如通过电流或照射光。本项目的目的是实验研究拓扑半金属的光学性质。在拓扑半金属中实现新的光学和光电子现象可能会导致有用的技术应用。具有拓扑物理和时间分辨光学技术专业知识的学生和博士后将被培养为这些领域的下一代科学家。该计划教育部分的一个关键部分是促进提高K-12数学和科学教育的质量，特别是在受社会经济影响的地区。技术文摘：Weyl半金属是一种新的物质拓扑相，预计将显示出迷人的性能。虽然利用角度分辨光发射光谱、扫描隧道显微镜和电输运系统地研究了电子能带结构和输运，但尽管预测了许多非常规的光学行为，但这些材料的光学性质在很大程度上仍未被探索。本研究计划的目的是研究拓扑半金属中手性Weyl费米子的新光学性质。特别是，据预测，在平行电场和磁场的存在下，具有不同手性的Weyl费米子会相互混合并产生依赖于磁场的电导率。这一现象被称为手性异常，仅凭输运测量很难得出结论。在本项目中，时间分辨光电流显微镜、瞬态光栅光谱和太赫兹光谱将用于光学检测Weyl半金属中的手性异常特征。此外，Weyl半金属的光电流响应将用于绘制其电子波函数的量子几何形状。这将允许探测到由Weyl节点产生的Berry曲率单极子和偶极子。在拓扑半金属中实现新的光学和光电子现象可能使我们能够通过光学手段控制Weyl费米子及其相关的量子异常，从而导致有用的光学和光电子应用。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。