Probing low energy excitations of topological semimetals

Non-technical Abstract: Quantum materials can host unique properties that are not possible in conventional materials. They can enable new technologies such as advanced electronics, photonics, computation and communication devices, sensors, and medical diagnostics that can be very energy efficient, ultrasensitive and process large amounts of information. Quantum materials typically utilize principles of quantum mechanics such as wave-like properties of matter which are very different from classical physics. There is a growing interest in new types of quantum materials with properties that are quite robust and not easily destroyed by local defects and disorder. Such materials are very promising for developing the next generation of optical and electronic devices. However, their properties need to be studied by developing new experimental tools. In this project, new optical tools and theoretical models will be developed to study a variety of novel quantum materials which will enable a deeper understanding of their properties. These studies will provide a generalized framework for development of new materials with novel device properties not possible with conventional approaches. The PI will utilize the experience obtained from working on the proposed ideas to augment the teaching curriculum at Penn, both at the undergraduate and graduate level. Research and educational activities will be integrated by the involvement of undergraduates in the research program, incorporating latest research results in the teaching module, and training high school and college teachers from the Philadelphia district. Technical Abstract: Topological quantum materials have novel properties originating from certain spatial and time reversal symmetries leading to electronic bands that host wavefunctions with unique topologies. In these systems, the wavefunction typically spreads over many lattices due to which the probes need to be sensitive to these large spreads with unique phase coherences. We will study the interplay of the crystal symmetries, band structure and topology in a variety of topological materials by developing new optical probes that are uniquely sensitive to their special properties. We will seek to obtain a deeper understanding of light-matter interactions in topological quantum materials by experimentally identifying new optoelectronic responses and describing nonlinear interactions to explain the contributions from symmetry, chirality, topology and other band features. We will design a variety of novel optical experiments that probe nonlocal interactions to study topological systems with long phase coherence lengths and derive nonlinear response functions to obtain microscopic insights about these materials and their dynamics. We will also attempt to understand how optical responses of quasiparticle excitations in topological systems are fundamentally different from trivial systems. Direct comparisons of measured responses between different topological material systems will enable a holistic understanding of the role of band crossings and topology in determining the properties of these systems. The proposed research will uncover novel properties and phenomena in emerging quantum materials where unique signatures of band textures will be accessed by using engineered light with intensity, phase and polarization. Our proposed work can lead to a new suite of nonlocal optoelectronic spectroscopies as a powerful, table-top tool to study complex material systems. Deeper understanding of topological materials may find applications in computing, photonics and sensing and will pave the way for novel devices enabled by active materials and new coupling mechanisms with robust functionalities. 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. NSF Award ID: 2508192 | Program: 01002627DB NSF RESEARCH & RELATED ACTIVIT | Principal Investigator: Ritesh Agarwal | Institution: University of Pennsylvania, PHILADELPHIA, PA | Award Amount: $524,546 View on NSF Award Search: https://www.nsf.gov/awardsearch/show-award/?AWD_ID=2508192 View on Research.gov: https://www.research.gov/awardapi-service/v1/awards/2508192.html