CAREER: Advancing theory of Resonant Inelastic X-ray Scattering for Materials In- and Out-of-Equilibrium

量子材料处于材料研究的前沿。在许多情况下，这些材料的显著特性源于它们的电子、磁性和结构特性之间微妙的相互作用。在过去的二十年里，谐振非弹性x射线散射已经成为这方面的一个强大的实验工具，因为它能够在一次实验中同时探测所有这些特性。但这种能力是有代价的，因为没有复杂的理论模型，这些实验很难解释；迫切需要新的理论工具。该职业奖支持旨在更好地理解共振非弹性x射线散射技术及其在几种新型量子材料中的应用的计算和理论研究和教育。该项目的目标是开发新的理论方法和计算机代码来模拟共振x射线散射实验。研究小组将与实验研究人员合作，应用这些方法来解决量子材料中的几个悬而未决的问题。该项目将为模拟共振x射线散射实验提供先进的理论工具，这些实验广泛适用于各种量子材料，从而有助于我们对这些系统的理解，并加速未来的发现。该项目的教育部分侧重于增加代表性不足的少数民族在高级物理研究中的参与。大约30%的大学适龄美国公民是少数种族群体的成员，但这些群体在科学、技术、工程和数学领域的代表性严重不足，其中最大的差距发生在物理领域。PI将带头在田纳西大学诺克斯维尔分校建立一个桥梁项目，与美国物理学会桥梁项目和美国国家科学基金会赞助的田纳西路易斯斯托克斯少数民族参与联盟项目合作。这些活动将有助于为那些不会申请或注册研究生院的学生创造进入物理研究生课程的另一种途径。该项目还支持本科生和研究生在物理学方面的研究机会，重点是先进的计算方法。强相关量子材料实现了广泛的科学和技术上重要的物质相。在许多情况下，这些系统的功能特性来源于它们的自旋、电荷、轨道和晶格激发的相互作用。在这种情况下，共振非弹性x射线散射（RIXS）已经成为一个强大的工具，能够同时访问所有这些激发在一个单一的实验。但如果没有理论模型，就很难解释RIXS的实验。此外，近年来泵浦探测或时间分辨RIXS实验的发展迫切需要新的理论工具。这个职业奖支持研究和教育朝着新的理论框架的发展建模平衡和时间分辨RIXS实验。该项目的主要目标是扩展最先进的数值方法，如密度矩阵重整化群，量子蒙特卡罗和嵌入式簇技术，以模拟平衡RIXS实验，然后将这些相同的方法整合到时间分辨RIXS实验的新理论中。研究小组将运用这些方法来解决几个悬而未决的问题。例子包括：1)识别量子自旋液体中的分数化准粒子激发并理解其平衡内外的动力学；2)确定相关量子材料中的集体磁和晶格激发的具体作用；3)建立RIXS如何提供回答这些问题的独特方法。其中许多问题将在自由电子激光设备（如直线加速器相干光源）上进行的实验中得到解决。该项目将为理解广泛适用于各种量子材料的RIXS实验提供一个先进的框架，从而为理解这些系统和加速未来的发现做出重大贡献。该项目的教育部分侧重于增加代表性不足的少数民族在高级物理研究中的参与。大约30%的大学适龄美国公民是少数种族群体的成员，但这些群体在科学、技术、工程和数学领域的代表性严重不足，其中最大的差距发生在物理领域。PI将带头在田纳西大学诺克斯维尔分校建立一个桥梁项目，与美国物理学会桥梁项目和美国国家科学基金会赞助的田纳西路易斯斯托克斯少数民族参与联盟项目合作。这些活动将有助于为那些不会申请或注册研究生院的学生创造进入物理研究生课程的另一种途径。该项目还支持本科生和研究生在物理学方面的研究机会，重点是先进的计算方法。该奖项反映了美国国家科学基金会的法定使命，并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，被认为值得支持。

NONTECHNICAL SUMMARYQuantum materials are at the forefront of materials research. In many cases, the remarkable properties of these materials derive from a subtle interplay between their electronic, magnetic, and structural properties. Over the last two decades, resonant inelastic x-ray scattering has emerged as a powerful experimental tool in this context, owing to its ability to simultaneously probe all of these properties in a single experiment. But this capability comes at a price, as these experiments are challenging to interpret without sophisticated theoretical models; there is an urgent need for new theoretical tools.This CAREER award supports computational and theoretical research and education aimed at obtaining a better understanding of resonant inelastic x-ray scattering techniques and their application to several novel quantum materials. The goal of the project is to develop new theoretical approaches and computer codes for modeling resonant x-ray scattering experiments. The research team will apply these methods to address several open questions in quantum materials, working in collaboration with experimental researchers. This project will provide advanced theoretical tools for modeling resonant x-ray scattering experiments that are broadly applicable to a wide range of quantum materials, thus contributing to our understanding of these systems and accelerating future discovery.This project's educational component focuses on increasing the participation of underrepresented minorities in advanced physics research. Approximately 30% of college-aged US citizens are members of racial minority groups, but these groups are drastically underrepresented in Science, Technology, Engineering, and Mathematics, with the largest disparity occurring in physics. The PI will spearhead the establishment of a Bridge Program at the University of Tennessee, Knoxville in partnership with the American Physical Society Bridge Program and the NSF-sponsored Tennessee Louis Stokes Alliance for Minority Participation Program. These activities will help create an alternative pathway into a physics graduate program for students who would not otherwise apply to or enroll in graduate school. This project also supports undergraduate and graduate research opportunities in physics with a focus on advanced computational methods.TECHNICAL SUMMARYStrongly correlated quantum materials realize a wide range of scientifically and technologically significant phases of matter. In many cases, the functional properties of these systems derive from the interplay of their spin, charge, orbital, and lattice excitations. In this context, resonant inelastic x-ray scattering (RIXS) has become a powerful tool, capable of simultaneously accessing all of these excitations in a single experiment. But RIXS experiments are difficult to interpret without theoretical models. Moreover, the recent development of pump-probe or time-resolved RIXS experiments has created an urgent need for new theoretical tools. This CAREER award supports research and education towards the development of new theoretical frameworks for modeling equilibrium and time-resolved RIXS experiments. The primary goals of this project are to extend state-of-the-art numerical methods like the density matrix renormalization group, quantum Monte Carlo, and embedded cluster techniques to model equilibrium RIXS experiments and then integrate these same approaches into new theory for time-resolved RIXS experiments. The research team will apply these methods to address several open problems. Examples include: 1) identifying fractionalized quasiparticle excitations in quantum spin liquids and understanding their dynamics both in and out of equilibrium, 2) determining the specific roles of the collective magnetic and lattice excitations in correlated quantum materials, and 3) establishing how RIXS provides a unique way of answering these questions. Many of these questions will be addressed in the context of ongoing experiments at free electron laser facilities like the Linac Coherent Light Source. This project will provide an advanced framework for understanding RIXS experiments that are broadly applicable to a wide range of quantum materials, thus contributing significantly to the understanding of these systems and accelerating future discovery. This project's educational component focuses on increasing the participation of underrepresented minorities in advanced physics research. Approximately 30% of college-aged US citizens are members of racial minority groups, but these groups are drastically underrepresented in Science, Technology, Engineering, and Mathematics, with the largest disparity occurring in physics. The PI will spearhead the establishment of a Bridge Program at the University of Tennessee, Knoxville in partnership with the American Physical Society Bridge Program and the NSF-sponsored Tennessee Louis Stokes Alliance for Minority Participation Program. These activities will help create an alternative pathway into a physics graduate program for students who would not otherwise apply to or enroll in graduate school. This project also supports undergraduate and graduate research opportunities in physics with a focus on advanced computational methods.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.