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

非技术摘要：该项目主要研究Weyl和Dirac半金属的光学性质。这些最近发现的新材料是具有最有趣的光学性质的半金属。拓扑相的存在导致以新的方式修改属性。例如，被保护不受散射的新状态被预测。这些特征有望在未来的应用中实现强大的电信号和光信号传输。虽然Weyl和Dirac半金属的一些例子已经在实验上被识别，但许多新的预测的光学性质还没有被研究。本项目的研究实验填补了这一空白。该项目培养一名研究生，一名博士后学者，并涉及一名兼职本科生。教育推广活动包括开发新的光学科学讲座演示实验。技术摘要：利用太赫兹光学和磁光技术对拓扑3D Dirac和Weyl材料进行的实验研究。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稳健的可调光学效果，直接探测新的性质和低激发态。Voigt几何中的磁光实验为手征反常的预测光学效应提供了一个极其灵敏的探测器，到目前为止，只有通过输运测量才能报道。克尔和法拉第的旋转测量测试了预测的磁光效应，这种效应是由与Weyl节点相关的底层Berry曲率(磁性)单极引起的。对焦绿石Iriates的磁光测量旨在证实在磁相变下存在Weyl态。几种狄拉克半金属在量子极限下的回旋共振研究直接探测了手征N=0朗道能级。这些活动还测试了最近预测这些材料新的奇异物理性质的理论。用FTIR零场反射和/或回旋共振透射率测量对所研究的所有材料体系的电子能带结构进行了光谱表征。该项目培养一名研究生，一名博士后学者，并涉及一名兼职本科生。教育宣传活动包括开发新的光学科学讲座演示实验。

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.