CAREER: Exciton-Phonon Coupling in Quantum Materials: Atomistic Insight for Defects and 2D Materials

University Of California - Merced, Merced CA

Investigators

Abstract

This award is funded in part under the American Rescue Plan Act of 2021 (Public Law 117-2). NONTECHNICAL SUMMARY This award supports theoretical and computational research and education activities aimed at improving fundamental understanding of the interaction of light and collective vibrations of atoms in materials. This interaction is important in many different phenomena such as changes in atomic structure after absorption of light or the changes in the energy of light due to interaction with atomic vibrations. These interactions are particularly significant when electrons and holes (the empty states left behind by excited electrons) are strongly bound. Such cases include atomically thin two-dimensional (2D) materials, and defects in materials where atoms are missing or added, which can also have unpaired electron spins that are difficult to handle theoretically. This project will develop more accurate and efficient quantum-mechanical computational methods to study interactions of light and vibrations, which will be validated by experimental measurements. The PI will then apply these methods to better understand phenomena in 2D materials and defects, allowing better predictions of which defects are promising for applications in quantum computing, and enabling identification of the elusive atomic structures of defects in 2D materials. The research in this project will benefit society and economic development by building the fundamental scientific knowledge for the advancement of quantum technologies including computing, communication, and sensing. The methods developed will be made available for wide use in the condensed matter theory community by implementation and release in open-source codes, and students and postdocs will be trained in best practices for code development. This project will also innovate in undergraduate education by introducing a Course-based Undergraduate Research Experience as a lab activity into the sophomore-level Modern Physics class at the University of California, Merced. The activity will teach students the role of computation in physics and show applications in current research. The template, evaluation data, and results of this activity will be disseminated in papers and presentations, to enable use in similar classes elsewhere. TECHNICAL SUMMARY This award supports theoretical and computational research and education activities aimed at improving fundamental understanding of exciton-phonon interactions in materials. Important experimentally measured phenomena involving exciton-phonon interactions include ultrafast motions after light absorption, resonant Raman spectroscopy, and vibronic features in optical spectra. In these phenomena, neglect of excitonic effects can give qualitatively different results, but exciton-phonon coupling has not been studied in detail theoretically due to lack of suitable approaches. Exciton-phonon coupling is generally strong in defects and two-dimensional (2D) materials, which are of great interest for quantum applications. Excitingly, developments in first-principles theory and massively parallel computation are now enabling accurate and efficient calculations of forces in the excited state for materials, via the GW approximation and Bethe-Salpeter equation. This project will develop and implement approaches for resonant Raman and vibronic spectra with excitonic effects, which will be applied to study 2D materials and defects for quantum information, including those with challenging triplet ground states. Collaboration with two experimental groups will validate and apply findings from this project. The research in this project will benefit society and economic development by building the fundamental scientific knowledge for the advancement of quantum technologies including computing, communication, and sensing. The methods developed will be made available for wide use in the condensed matter theory community by implementation and release in open-source codes, and students and postdocs will be trained in best practices for code development. This project will also innovate in undergraduate education by introducing a Course-based Undergraduate Research Experience as a lab activity into the sophomore-level Modern Physics class at the University of California, Merced. The activity will teach students the role of computation in physics and show applications in current research. The template, evaluation data, and results of this activity will be disseminated in papers and presentations, to enable use in similar classes elsewhere. 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.