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

该奖项的部分资金来自2021年美国救援计划法案（公法117-2）。非技术总结该奖项支持理论和计算研究和教育活动，旨在提高对光的相互作用和材料中原子集体振动的基本理解。这种相互作用在许多不同的现象中是重要的，例如吸收光后原子结构的变化或由于与原子振动相互作用而引起的光能量的变化。当电子和空穴（被激发的电子留下的空态）被强烈束缚时，这些相互作用特别重要。这种情况包括原子薄的二维（2D）材料，以及原子缺失或添加的材料中的缺陷，这些缺陷也可能具有理论上难以处理的未成对电子自旋。该项目将开发更准确和有效的量子力学计算方法来研究光和振动的相互作用，并将通过实验测量进行验证。然后，PI将应用这些方法来更好地理解2D材料和缺陷中的现象，从而更好地预测哪些缺陷在量子计算中有应用前景，并能够识别2D材料中缺陷的难以捉摸的原子结构。该项目的研究将通过为包括计算，通信和传感在内的量子技术的进步建立基础科学知识，从而造福社会和经济发展。开发的方法将通过实施和发布开源代码在凝聚态理论社区中广泛使用，学生和博士后将接受代码开发最佳实践的培训。该项目还将通过将基于课程的本科生研究体验作为实验室活动引入加州大学默塞德分校的本科生现代物理课程来创新本科生教育。该活动将教授学生计算在物理学中的作用，并展示其在当前研究中的应用。该活动的模板、评估数据和结果将在论文和演示文稿中传播，以便在其他地方的类似课程中使用。技术概要该奖项支持旨在提高对材料中激子-声子相互作用的基本理解的理论和计算研究和教育活动。涉及激子-声子相互作用的重要实验测量现象包括光吸收后的超快运动、共振拉曼光谱和光谱中的电子振动特征。在这些现象中，忽略激子效应可以得到定性的不同结果，但是激子-声子耦合由于缺乏合适的方法而没有在理论上进行详细的研究。激子-声子耦合通常在缺陷和二维（2D）材料中很强，这对量子应用非常感兴趣。令人兴奋的是，第一性原理理论和大规模并行计算的发展现在可以通过GW近似和Bethe-Salpeter方程精确有效地计算材料激发态的力。该项目将开发和实施具有激子效应的共振拉曼和振动光谱的方法，这些方法将用于研究量子信息的二维材料和缺陷，包括具有挑战性的三重基态。与两个实验小组的合作将验证和应用该项目的结果。该项目的研究将通过为包括计算，通信和传感在内的量子技术的进步建立基础科学知识，从而造福社会和经济发展。开发的方法将通过实施和发布开源代码在凝聚态理论社区中广泛使用，学生和博士后将接受代码开发最佳实践的培训。该项目还将通过将基于课程的本科生研究体验作为实验室活动引入加州大学默塞德分校的本科生现代物理课程来创新本科生教育。该活动将教授学生计算在物理学中的作用，并展示其在当前研究中的应用。该活动的模板、评估数据和结果将在论文和演示文稿中传播，以便在其他地方的类似课程中使用。该奖项反映了NSF的法定使命，并被认为值得通过使用基金会的知识价值和更广泛的影响审查标准进行评估来支持。

This award is funded in part under the American Rescue Plan Act of 2021 (Public Law 117-2).NONTECHNICAL SUMMARYThis 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.