CAREER: Sub-Picosecond Electron Dynamics in Complex Electron Systems

****技术摘要****铜高温超导体等复杂电子系统（CES）表现出电荷自由度、晶格自由度和自旋自由度之间相互作用和竞争的非常规现象。揭开这种相互作用的细节将促进对复杂材料功能背后的物理原理的理解。在自由度之间建立因果关系的不可能性阻碍了理解它们之间的相互作用。本文讨论了一种独特的实验方法，有望克服这一挑战。它的基础是将超快测量技术扩展到以飞秒激光器为光子源的角度分辨光电发射实验。时间分辨率允许在比潜在相关性更短的时间尺度上激发CES中不同自由度的耦合，并通过在相关性发展时探测它们的时间响应来对这些相互作用进行分类。基于激发态的动态响应，建立了不同自由度间的时间层次。田纳西大学拟议的科学和配套基础设施为年轻学生的教育和培训提供了良好的环境。我们的教育计划利用这些资源的可用性，在为本科生创造新的研究机会和为高中生制定详细计划的基础上，具体地努力将研究和教育结合起来。****非技术摘要****在复杂电子系统（CES）中，电子通过它们的电荷、晶格或自旋相互作用，产生了壮观和非常规的现象，如高温超导。CES研究的一个主要挑战是无法在相互作用之间建立因果关系，从而阻碍了对复杂材料的正确理解。本文讨论了一种独特的实验方法，有望克服这一挑战。它是基于感应电子发射，与超短（不到十亿分之一秒！）脉冲紫外线辐射。对发射电子的分析提供了关于电子如何在材料中相互作用的重要信息。这些脉冲可以如此迅速地激发电子，从而瞬间破坏它们之间的相互作用。然后在这些初始激发之后监测电子。当相互作用开始重新形成时，将有可能在电子光谱中观察到它们的特征。因此，通过探测激发态在时间上的响应，可以解开相互作用的纠缠，并有可能在它们之间建立一个时间层次。田纳西大学拟议的科学和配套基础设施为年轻学生的教育和培训提供了良好的环境。我们的教育计划利用这些资源的可用性，在为本科生创造新的研究机会和为高中生制定详细计划的基础上，具体地努力将研究和教育结合起来。

****Technical Abstract****Complex electron systems (CES) such as cuprate high-temperature superconductors exhibit unconventional phenomena emerging from the interplay and competition among the charge-, lattice- and spin-degrees of freedom. Unraveling the details of this interplay will foster understanding of the physics at play behind the functionality of complex materials. The impossibility of establishing cause-effect relationships among the degrees of freedom hampers understanding their interplay. This Proposal discusses a unique experimental approach promising the overcome of this challenge. It is based on the extension of ultrafast measurement techniques to Angle Resolved Photoemission experiments using femtosecond lasers as photon sources. The time resolution allows disentangling the coupling of different degrees of freedom in CES by exciting them on timescales shorter than the underlying correlations, and to sort out these interactions by probing their time response as the correlations develop. A time hierarchy among different degrees of freedom is established based on the dynamical response of the excited electron states. The proposed science and supporting infrastructure at the University of Tennessee provide an excellent setting for the education and training of young students. Our educational plan exploits the availability of these resources in a concrete effort to integrate research and education based on creating new research opportunities for undergraduate students and a detailed plan to reach high school students.****Non-Technical Abstract****In complex electron systems (CES), electrons interact among each other via their charge, lattice, or spin, giving rise to spectacular and unconventional phenomena such as high temperature superconductivity. A major challenge in the study of CES is the problem of being unable to establish a cause-effect relationship among the interactions, thus hampering a sound understanding of complex materials. This Proposal discusses a unique experimental approach promising the overcome of this challenge. It is based on inducing electrons emission, with ultra-short (less than a billionth of a second!) pulses of ultraviolet radiation. Analyses of the emitted electrons provide important information about how electrons interact in a material. These pulses can excite electrons so quickly so as to instantaneously destroy their interactions. Electrons are then monitored following these initial excitations. When the interactions start to re-form, it will be possible to observe their signature in the electronic spectra. The interactions will thus be disentangled by probing the response in time of the excited electron states, with the possibility of establishing a time hierarchy among them. The proposed science and supporting infrastructure at the University of Tennessee provide an excellent setting for the education and training of young students. Our educational plan exploits the availability of these resources in a concrete effort to integrate research and education based on creating new research opportunities for undergraduate students and a detailed plan to reach high school students.