THz magneto-optical studies of 3-D topological Dirac and Weyl semimetals

非技术摘要：该项目重点研究外尔和狄拉克半金属的光学性质。这些最近发现的新型材料是具有最有趣的光学特性的半金属。拓扑相的存在导致属性以新的方式发生变化。例如，预测免受散射的新状态。这些功能有望在未来的应用中实现可靠的电信号和光信号传输。虽然已经通过实验鉴定了许多外尔和狄拉克半金属的例子，但许多新颖的预测光学性质尚未得到研究。本项目的研究实验填补了这一空白。项目培养研究生1名，博士后1名，非全日制本科生1名。教育推广活动包括开发光学科学领域的新讲座演示实验。技术摘要：拓扑 3D 狄拉克和韦尔材料的实验研究利用太赫兹光学和磁光技术。这些半金属材料是一类新型材料，具有相对较低的载流子密度和电导，能够在太赫兹频率下实现强大的可调谐光学效应，从而直接探测新颖的特性和低位激发。福伊特几何中的磁光实验提供了一种极其灵敏的探针，可以预测手性异常的光学效应，迄今为止，这种效应仅通过输运测量得到报告。克尔和法拉第旋转测量测试了预测的类磁光效应，该效应是由与韦尔节点相关的底层贝里曲率（磁性）单极子引起的。对烧绿石铱酸盐的磁光测量旨在确认磁转变以下韦尔态的存在。对几种狄拉克半金属在极端量子极限下的回旋共振研究直接探测手性 N=0 朗道能级。这些活动还测试了预测这些材料新奇特物理特性的最新理论。所有研究材料系统的电子能带结构均通过 FTIR 零场反射率和/或回旋共振透射测量进行光谱表征。项目培养研究生1名，博士后1名，非全日制本科生1名。教育推广活动包括开发光学科学领域的新讲座演示实验。

Non-technical Abstract:The project focuses on the investigations of the optical properties of Weyl and Dirac semimetals. These recently discovered new classes of materials are semimetals with most interesting optical properties. The presence of topological phases results in modifications of the properties in new ways. For example, new states which are protected from scattering are predicted. These features have promise for robust transport of electrical and optical signals useful in future applications. While a number of examples of the Weyl and Dirac semimetals have been identified experimentally, many of the novel predicted optical properties have not yet been investigated. The research experiments in this project fill this gap. The project trains one graduate student, one post-doctoral scholar, and involves one part time undergraduate. Educational outreach activities include development of new lecture demonstration experiments in the optical sciences.Technical Abstract:The experimental investigations of topological 3D Dirac and Weyl materials leverage terahertz optical and magneto-optical techniques. These semimetallic materials are a new class of materials that have relatively low carrier density and conductance, enabling robust tunable optical effects at terahertz frequencies that directly probe the novel properties and low-lying excitations. Magneto-optical experiments in the Voigt geometry offers an extremely sensitive probe of the predicted optical effects from the chiral anomaly that, so far, has only been reported by transport measurements. Kerr and Faraday rotation measurements test predicted magneto-optical-like effects that arise from the underlying Berry curvature (magnetic) monopoles associated with the Weyl nodes. Magneto-optical measurements on the pyrochlore Iridates aim at confirming the presence of the Weyl state below the magnetic transition. Cyclotron resonance investigations of several Dirac semimetals in the extreme quantum limit directly probe the chiral N=0 Landau level. The activities also test recent theories that predict new exotic physical properties of these materials. The electronic band structure of all studied material systems are characterized spectroscopically with FTIR zero-field reflectance and/or cyclotron resonance transmission measurements. The project trains one graduate student, one post-doctoral scholar, and involves one part time undergraduate. Educational outreach activities include development of new lecture demonstration experiments in the optical sciences.