Theoretical description of pump-probe spectroscopies in solids

超快材料科学位于凝聚态物理学和超快光谱学之间的边界，凝聚态物理学研究固体中许多相互作用粒子的集体物理学，超快光谱学研究小长度尺度和超短时间尺度上光与物质的相互作用。一种方法是用短激光脉冲（“泵”）刺激一个复杂的多粒子系统，使其脱离热平衡，以便随后用第二脉冲（“探针”）监测激发态动力学。这个研究项目的目标是在微观层面上从理论上理解从泵浦激光器进入固体的能量流。重要的是，这种理解必须将多粒子材料科学语言与超快科学的非平衡性质联系起来。特别是，我计划研究有序机制及其在有序状态下的激光操作，如超导体和电荷密度波。从另一个角度来看，电子和离子晶格之间的相互作用可以通过直接驱动晶格运动来控制。我计划研究晶格驱动如何帮助从电子-晶格耦合驱动机制中分离纯电子排序机制。最后，我将研究如何创建新的光-物质耦合状态，这使得在泵浦激光存在下可以调整材料特性。为此，我将使用Keldysh Green函数技术，它自然地将多粒子和非平衡物理联系起来。我将在现有的计算机代码的基础上，对泵浦探测光谱进行广泛的数值模拟，这些代码是我们在过去几年中开发的。拟议的项目将有助于指导实验工作，并为进一步的理论发展铺平道路，以便平等地理解电子，晶格和泵浦激光光子的动态相互作用，并利用所学到的经验教训来设计具有更好功能的优化材料。

Ultrafast materials science is located at the boundary between condensed matter physics, which investigates the collective physics of many interacting particles in solids, and ultrafast spectroscopy, which investigates light-matter interactions on small length scales and on ultrashort time scales. One takes a complex many-particle system out of its thermal equilibrium by stimulation with a short laser pulse ("pump"), in order to subsequently monitor the excited state dynamics with a second ("probe") pulse. The goal of this research project is to theoretically understand the flow of energy from the pump laser into the solid on a microscopic level. Importantly, this understanding must connect the many-particle materials science language with the non-equilibrium nature of ultrafast science. In particular, I plan to investigate ordering mechanisms and their laser manipulation in ordered states, such as superconductors and charge-density waves. From a different angle, the interaction between the electrons and the ionic lattice can be manipulated by directly driving the lattice motion. I plan to investigate how lattice driving can help disentangle purely electronic ordering mechanisms from electron-lattice coupling driven mechanisms. Finally, I will study how new light-matter coupled states can be created, which enable tuning of the material properties in the presence of the pump laser. To this end, I will employ the Keldysh Green function technique, which naturally connects many-particle and non-equilibrium physics. I will use extensive numerical simulations for pump-probe spectroscopies, building upon existing computer codes, which were developed by us in the past few years. The proposed project will help guide experimental efforts as well as pave the way for further theoretical developments, in order to understand the dynamical interplay of electrons, lattice, and pump laser photons on an equal footing and to use the lessons learned in order to design optimized materials with better functionalities.