CAREER: Sub-Picosecond Electron Dynamics in Complex Electron Systems

*复杂电子系统(CES)，如铜酸盐高温超导体，由于电荷自由度、晶格自由度和自旋自由度之间的相互作用和竞争，呈现出非常规的现象。揭开这种相互作用的细节将有助于理解复杂材料功能背后的物理作用。不可能在自由度之间建立因果关系，这妨碍了理解它们之间的相互作用。该提案讨论了一种独特的实验方法，有望克服这一挑战。它是基于将超快测量技术扩展到使用飞秒激光作为光子源的角度分辨光电子发射实验。时间分辨率允许通过在比潜在相关性更短的时间尺度上激发CES中的不同自由度来解开它们的耦合，并通过探测它们随着相关性的发展而产生的时间响应来分类这些相互作用。根据激发电子态的动力学响应，建立了不同自由度之间的时间序列。田纳西大学拟议的科学和辅助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，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，将研究和教育结合起来。*非技术摘要*在复杂电子系统(CES)中，电子通过电荷、晶格或自旋相互作用，产生壮观的和非常规的现象，如高温超导。CES研究中的一个主要挑战是无法建立相互作用之间的因果关系，从而阻碍了对复杂材料的正确理解。该提案讨论了一种独特的实验方法，有望克服这一挑战。它是基于诱导电子发射的，具有超短(不到十亿分之一秒！)紫外线辐射的脉冲。对发射电子的分析提供了有关电子在材料中如何相互作用的重要信息。这些脉冲可以如此迅速地激发电子，从而瞬间摧毁它们的相互作用。然后在这些初始激发之后对电子进行监测。当相互作用开始重新形成时，就有可能在电子光谱中观察到它们的签名。因此，通过探测激发电子态的时间响应，相互作用将被解缠，并有可能在它们之间建立时间层次。田纳西大学拟议的科学和辅助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，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，具体努力整合研究和教育。

****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.