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

摘要：本项目主要研究Weyl和Dirac半金属的光学性质。这些最近发现的新型材料是半金属，具有最有趣的光学性质。拓扑相的存在以新的方式改变了材料的性质。例如，预测了不受散射影响的新态。这些特性保证了在未来应用中有用的电信号和光信号的鲁棒传输。虽然Weyl和Dirac半金属的一些例子已经在实验中被确定，但许多新的预测光学性质尚未被研究。本项目的研究实验填补了这一空白。本项目培养研究生1人，博士后1人，兼职本科生1人。教育外展活动包括发展光学科学的新讲座示范实验。技术摘要：拓扑三维Dirac和Weyl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率，可以在太赫兹频率下实现鲁棒可调光学效应，直接探测新特性和低空激发。Voigt几何中的磁光实验为预测手性异常的光学效应提供了一个极其敏感的探针，到目前为止，只有通过输运测量才有报道。Kerr和Faraday旋转测量测试预测了由与Weyl节点相关的底层Berry曲率（磁）单极子产生的类磁光效应。对焦绿石铱酸盐的磁光测量旨在确认磁跃迁下Weyl态的存在。在极端量子极限下对几种狄拉克半金属的回旋共振研究直接探测了手性N=0朗道能级。这些活动也验证了预测这些材料新的奇异物理特性的最新理论。通过FTIR零场反射和/或回旋共振透射测量，对所有研究材料体系的电子能带结构进行了光谱表征。本项目培养研究生1人，博士后1人，兼职本科生1人。教育外展活动包括发展光学科学的新讲座示范实验。

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.