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

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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.