CAREER: Infrared and Terahertz Electrodynamics of Chiral Materials

非技术：该职业奖支持新发现的手性拓扑材料的电子和光子特性的实验研究和教育。手性物体是指不能与其镜像重叠的物体，比如左手和右手。氨基酸是众所周知的手性物质。拓扑材料具有有趣的特性，这使得它们对开发先进的电子和光子器件非常有用。例如，拓扑绝缘体是量子物质的一种状态，它在内部表现为绝缘体，但在表面表现为导体。手性材料和拓扑材料在自然界中随处可见，这些现象往往是耦合的。了解用光产生手性载流子的机理对于低损耗和偏振选择性光探测器等光电应用具有重要意义。本项目旨在通过研究手性拓扑材料在受控温度、应变和磁场条件下的本征光物质相互作用，促进对手性拓扑材料的认识。太赫兹（THz）和远红外（IR）频率的光谱学将以纳米级空间分辨率和飞秒时间分辨率进行。这项研究为红外和太赫兹光的探测和传感以及接近室温的超快开关提供了令人着迷的机会。本研究为研究新的拓扑结构和光子器件开辟了新的途径。这些研究将为年轻研究人员提供包括太赫兹纳米镜和光谱学在内的广泛学科的复杂培训。技术方面：在三维手性材料中，手性电荷电流是由具有非平凡拓扑结构的外部规范场（如平行电场和磁场或圆偏振光）引起的手性不平衡产生的。这种所谓的“手性磁效应”产生了有趣的手性异常现象，如几乎非耗散输运和大的负磁阻。手性异常可能会出现在大量接近平凡绝缘体和拓扑绝缘体之间过渡的材料中，例如ZrTe5， TaAs， HfTe5等。在本项目中，研究小组研究了横向尺寸低于和高于手性载流子谷弛豫长度的手性微晶体和光子器件的光电子特性。该团队计划表征手性材料的低能激发谱（0.1-15太赫兹），并利用它们使用圆偏振光产生超快光电流的能力。利用磁场效应或应变效应可以系统地研究晶体中超快光电流的产生及其产生的太赫兹辐射。该研究还确定了手性波段在远红外和近红外频率范围内的光转换中所涉及的程度，以及它将红外光转换为太赫兹辐射或反之亦然的能力。所有的实验方案都可以推广到其他具有破缺时间或空间反演对称性的光子微晶体或器件中。该领域的研究可以深刻拓宽手性敏感光电子学的物理基础知识，为实现非平凡的光敏和光伏效应开辟新的途径。该团队将与不同群体的本科生和研究生密切合作，特别是那些来自代表性不足的少数民族的学生，以开发新的研究活动，如用于可重构光学元件的教育3D打印。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:This CAREER award supports experimental research and education on the electronic and photonic properties of newly discovered chiral topological materials. A chiral object is something that cannot be superimposed on its mirror image, like a left and a right hand. Amino acids are well-known chiral materials. Topological materials have interesting properties that make them useful for developing advanced electronic and photonic devices. For example, a topological insulator is a state of quantum matter that behaves as an insulator in its interior but as a conductor on its surface. Chiral and topological materials are found throughout nature, and these phenomena are often coupled. Understanding the mechanism of generating chiral charge carriers with light is important for optoelectronic applications such as low-loss and polarization-selective light detectors. The project aims to advance the understanding of chiral topological materials through study of the intrinsic light-matter interaction in the under conditions with controlled temperature, strain, and magnetic-fields. Spectroscopy at terahertz (THz) and far infrared (IR) frequencies will be performed with nanoscale spatial resolution and femtosecond time resolution. This research effort offers fascinating opportunities for detection and sensing of IR and THz light and ultrafast switching at close to room temperature. The activities enabled by this research can open new routes to study novel topologies and photonic devices. These studies will provide sophisticated training to young researchers in a broad range of subjects including THz nanoscopy and spectroscopy. Technical:In three dimensional chiral materials, chiral charge current can be generated via the chirality imbalance induced by external gauge fields with non-trivial topology such as parallel electric and magnetic fields or circularly polarized light. This so-called “chiral magnetic effect” yields interesting chiral anomaly phenomenon such as nearly non-dissipative transport and large negative magnetoresistance. The chiral anomalies will likely emerge in a wide class of materials that are near the transition between trivial and topological insulators, e.g. ZrTe5, TaAs, HfTe5, etc. In this project, the research team investigate photoelectronic properties of chiral microcrystals and photonic devices with lateral sizes below and above the valley relaxation length of chiral carriers. The team plans to characterize the low energy excitation spectrum (0.1-15 THz) of chiral materials and exploit their ability to generate ultrafast photocurrent using circularly polarized light. Ultrafast photocurrent generation and its resultant THz emission in crystals can be systematically studied with magnetic field or strain induced effect. The research also determines how much the chiral band is involved in the light conversion between the far-IR and near-IR frequency ranges and its capability to turn IR light to THz emission or vice versa. All the experimental schemes can be extended to other photonic microcrystals or devices with broken time or spatial inversion symmetries. Research in this area can profoundly broaden the fundamental knowledge of physics in chirality-sensitive optoelectronics and open new routes to achieve non-trivial photosensing and photovoltaic effects. The team will work closely with a diverse group of undergraduate and graduate students, especially those from underrepresented minorities, to develop novel research activities such as educational 3D printing for reconfigurable optical components.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.