CAREER: Sub-Picosecond Electron Dynamics in Complex Electron Systems

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****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.