CAREER: Infrared and Terahertz Electrodynamics of Chiral Materials

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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.