CAREER: Real-Time First-Principles Approach to Understanding Many-Body Effects on High Harmonic Generation in Solids

该奖项支持研究，教育和推广活动，重点是了解电子之间的相互作用如何改变材料在暴露于非常强的电磁场时的行为方式。强电磁场以高度非线性的方式与材料相互作用。在这些高场中出现的一种现象是高次谐波产生--一种低能量光被材料吸收并结合以产生能量为入射光的整数倍（或谐波）的光的过程。这种高次谐波的产生对于超快光源的发展是至关重要的，超快光源可用于在非常短的时间尺度上探测电子和原子运动的物理学。大多数现有的高次谐波产生源依赖于从原子和分子的气体产生，其中电子的允许能级是离散的。将这些过程从气相扩展到结晶固体，在入射和产生的光可以访问的能量范围中引入了更大的灵活性。固体中高次谐波光的产生也可以潜在地用作表征这些固体中电子行为的工具。然而，固体中的高次谐波光谱的解释是非常具有挑战性的，由于复杂的相互作用的电子和原子的运动，有助于在不同的生成条件下的出射光的产量。该项目旨在开发，实施和应用新的理论和计算工具，以帮助理解电子运动和相互作用在固体高次谐波产生中的作用。所开发的方法将被应用于研究高谐波产生低维固体中的电子相互作用预计会很强。该项目支持博士后研究人员和研究生的教育。此外，该项目将整合研究，教育和指导与脚手架外展计划，旨在扩大历史上在科学和工程中代表性不足的群体的参与。PI将开发新的本科材料科学课程和夏季材料科学研讨会，并为纽黑文公立学校系统的学生提供年度夏季实习。拟议的推广包括一个严格的数据收集组件，将允许该计划的影响进行assessed.Technical SUMMARYThis奖项支持研究，教育和推广活动，重点是了解多体效应在非微扰高谐波发电。固体中的高次谐波产生是在极紫外区产生新的阿秒光源的基础，并有望成为材料能带结构和拓扑结构的全光学探针。然而，能够描述真实的材料中非微扰高次谐波产生的理论仍然处于萌芽状态，特别是在对多体效应进行定量理解时。本项目旨在开发和应用一种新的从头算方法，该方法基于非平衡多体态的Keldysh形式主义，以了解高次谐波产生和其他非线性光谱学中的多体效应。该方法是建立在依赖于时间的绝热GW的方法（这里，G代表的单粒子绿色的功能和W是屏蔽库仑相互作用），其中的单粒子密度矩阵耦合到一个外部场和传播的时间与从头算GW自能。PI和她的团队将把这种方法应用于（1）通过在二维材料的测试平台上进行计算来理解高次谐波光谱中的拓扑结构、自旋、极化纹理和激子效应的特征，其中激子结合能、屏蔽和对称性等复杂因素可以更容易地分离出来;以及（2）了解我们的计算技术和组分近似的局限性。2这个项目支持博士后研究人员和研究生的教育。此外，该项目将整合研究，教育和指导与脚手架外展计划，旨在扩大历史上在科学和工程中代表性不足的群体的参与。PI将开发新的本科材料科学课程和夏季材料科学研讨会，并为纽黑文公立学校系统的学生提供年度夏季实习。该奖项反映了NSF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 SummaryThis award supports research, education, and outreach activities focused on understanding how interactions between electrons change the way that materials behave when exposed to very strong electromagnetic fields. Strong electromagnetic fields interact with materials in a highly nonlinear way. One phenomenon that arises in these high fields is high harmonic generation—a process where low-energy light is absorbed by a material and combined to produce light at energies that are integer multiples (or harmonics) of the incoming light. Such high harmonic generation is fundamental for the development of ultrafast light sources that can be used to probe the physics of electronic and atomic motion on very short timescales. Most existing sources of high harmonic generation rely on generation from gases of atoms and molecules, where the allowed energy levels of the electrons are discrete. Extending these processes from the gas phase to crystalline solids introduces greater flexibility in the energy ranges that can be accessed by the incoming and generated light. The generation of high harmonic light in solids can also potentially be used as a tool for characterizing the behavior of electrons in these solids. However, the interpretation of high harmonic spectra in solids is highly challenging due to the complicated interplay of electronic and atomic motion that contribute to the yield of outgoing light under different generation conditions. This project aims to develop, implement, and apply new theoretical and computational tools to aid in understanding the role of electron motion and interactions in high harmonic generation from solids. The developed methods will be applied to study high harmonic generation in low-dimensional solids where electron interactions are expected to be strong.This project supports a postdoctoral researcher and the education of a graduate student. Additionally, this project will integrate research, education, and mentoring with a scaffolded outreach program designed to broaden the participation of groups that are historically under-represented in science and engineering. The PI will develop a new undergraduate materials science curriculum and a summer materials science workshop and offer a yearly summer internship for students from the New Haven public school system. The proposed outreach includes a rigorous data collection component that will allow the impact of the program to be assessed.TECHNICAL SUMMARYThis award supports research, education, and outreach activities focused on understanding many-body effects in nonperturbative high harmonic generation. High harmonic generation in solids is foundational for the creation of new attosecond light sources across the extreme ultraviolet regime and holds promise as an all-optical probe of materials’ bandstructure and topology. However, theory that can describe nonperturbative high harmonic generation in real materials is still nascent, especially when it comes to a quantitative understanding of many-body effects. This project aims to develop and apply a new ab initio method based on the Keldysh formalism for nonequilibrium many-body states to understand many-body effects in high harmonic generation and other nonlinear spectroscopies beyond the perturbative regime. The method is built on the time-dependent adiabatic GW approach (here, G stands for the one-particle Green’s function and W is the screened Coulomb interaction), where the one-particle density matrix is coupled to an external field and propagated in time with the ab initio GW self-energy. The PI and her team will apply this approach to (1) to understand signatures of topology, spin, polarization textures, and exciton effects in high harmonic spectra by performing calculations on a testbed of two-dimensional materials, where complex factors like exciton binding energy, screening, and symmetry can be more easily isolated; and (2) understand the limits of our computational techniques and constituent approximations.This project supports a postdoctoral researcher and the education of a graduate student. Additionally, this project will integrate research, education, and mentoring with a scaffolded outreach program designed to broaden the participation of groups that are historically under-represented in science and engineering. The PI will develop a new undergraduate materials science curriculum and a summer materials science workshop and offer a yearly summer internship for students from the New Haven public school system. The proposed outreach includes a rigorous data collection component that will allow the impact of the program to be assessed.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.