Dynamics of Localized Photoexcitations in Condensed Matter Systems

技术摘要：电子态的局域化在决定各种材料的性质方面起着至关重要的作用：极化子的形成对电子材料的电荷输运性质有着深远的影响，自陷激子或激子-极化子的形成极大地改变了光学性质和能量输运机制。 虽然准粒子的平衡性质在许多系统中得到了很好的建立，但对准粒子形成过程的动力学还没有完全理解。 除了其基本意义外，这些知识还提供了一种理解并从而利用材料的快速电子和光学响应的方法。 该项目包括研究本地化固有的耦合电子和振动动力学，在准一维材料中进行，其中驱动本地化动力学的电子-声子相互作用的强度可以系统地调整。 这些系统的研究将使用飞秒时间分辨技术，是敏感的电子，振动和结构动力学。 时间分辨光谱和X射线技术的协同组合，加上理论建模，有望提高光致结构变化的理解，无论是在这些系统和更普遍的。 非技术摘要：电子态的局域化在确定各种材料的性质方面起着关键作用。 局域电荷载流子或极化子的形成对电子材料的电荷输运性质具有深远的影响，并且局域电子激发（自陷激子或激子-极化子）的形成显著地改变光学性质和能量输运机制。 除了其基本意义外，对局域化过程的基本物理学的了解还有望成为理解并利用材料的快速电子和光学响应的手段。 该项目研究本地化固有的耦合电子和振动动力学，在驱动本地化动力学的电子-声子相互作用的强度可以系统地调整的材料中进行。对这些材料的研究将使用对电子、振动和结构动力学敏感的超快时间分辨技术来完成。时间分辨光谱和X射线技术的协同组合，加上理论建模，有望提高光致结构变化的理解，无论是在这些系统和更普遍的。该项目将支持2博士的工作。学生涉及凝聚态物理学基本问题的基础研究与实验开发中的实际问题相结合，提供了一个很好的培训场所;在电子材料超快光谱学领域工作的学生为进入学术界，政府实验室和高科技行业做好了充分的准备，因为他们在基础和应用工作方面都有背景。

Technical abstract:Localization of electronic states plays a critical role in determining the properties of a wide range of materials: polaron formation has a profound impact on the charge transport properties of electronic materials, and formation of self-trapped excitons, or exciton-polarons, dramatically changes optical properties and energy transport mechanisms. While the equilibrium properties of quasiparticles are well-established in many systems, a full understanding of the dynamics of the process of quasiparticle formation has yet to be achieved. In addition to its fundamental significance, such knowledge promises a means to understand, and thereby exploit, the fast electronic and optical response of materials. This project consists of studies of the coupled electronic and vibrational dynamics inherent to localization, carried out in quasi-one-dimensional materials in which the strength of the electron-phonon interactions that drive the localization dynamics can be systematically tuned. Studies of these systems will be accomplished using femtosecond time-resolved techniques that are sensitive to electronic, vibrational, and structural dynamics. The synergistic combination of time-resolved spectroscopic and x-ray techniques, together with theoretical modeling, promises to enhance the understanding of photoinduced structural changes, both in these systems and more generally. Non-technical abstract:Localization of electronic states plays a critical role in determining the properties of a wide range of materials. The formation of localized charge carriers, or polarons, has a profound impact on the charge transport properties of electronic materials, and the formation of localized electronic excitations (self-trapped excitons or exciton-polarons) dramatically changes optical properties and energy transport mechanisms. In addition to its fundamental significance, knowledge of the underlying physics of localization processes promises a means to understand, and thereby exploit, the fast electronic and optical response of materials. This project studies the coupled electronic and vibrational dynamics inherent to localization, carried out in materials in which the strength of the electron-phonon interactions that drive the localization dynamics can be systematically tuned. Studies of these materials will be accomplished using ultrafast time-resolved techniques that are sensitive to electronic, vibrational, and structural dynamics. The synergistic combination of time-resolved spectroscopic and x-ray techniques, together with theoretical modeling, promises to enhance the understanding of photoinduced structural changes, both in these systems and more generally. This project will support the work of 2 Ph.D. students. The combination of basic research involving fundamental issues in condensed matter physics with practical issues in experiment development provides an excellent training ground; students working in ultrafast spectroscopy of electronic materials are well-prepared to enter positions in academia, government laboratories, and hightech industry, given their background in both basic and applied work.