Dynamics of Localized Photoexcitations in Condensed Matter Systems Susan L. Dexheimer, Washington State University, DMR The localization of electronic states is a phenomenon that has a dramatic impact on optical and electronic properties of materials and reflects fundamental interactions in the physics of condensed matter systems. We are investigating the physics of the formation of localized electronic excitations using state-of-the-art time-resolved techniques with femtosecond ( s) resolution that are sensitive to both electronic dynamics and atomic-scale vibrational motions, including coherent vibrational, optical, terahertz, and x-ray methods. In addition to its fundamental significance, such knowledge promises a means to understand, and thereby exploit, the fast electronic and optical response of materials. In our recent work, 1 we time-resolved the formation of exciton- polarons in a series of materials in which the strength of the electron-phonon interaction that drives the dynamics can be systematically tuned from the small polaron limit, in which the localization length approaches a single unit cell of the lattice, to the large polaron limit, in which the excitation extends over a large number of unit cells. We find that the polaron forms on the time scale of a single vibrational period, approaching the fastest physically possible limit for the structural transformation, and we find a striking variation in the extent of the softening of the accompanying optical phonon mode, which we have related to the extent of the electronic delocalization. We anticipate that these results will provide an important benchmark for the development of theoretical models for the dynamics of quasiparticle formation. Structurally tunable quasi-one-dimensional mixed-valence linear chains: [Pt(en) 2 ][Pt(en) 2 X 2 ]. ClO 4 X = Cl, Br, I (en) = ethylenediamine (C 2 H 8 N 2 )... 1 F X Morrissey, J G Mance, A D Van Pelt, and S L Dexheimer, Femtosecond dynamics of exciton localization: Self-trapping from the small to the large polaron limit, J. Phys.: Condens. Matter 25 (2013) This paper was highlighted in an Institute of Physics LabTalk news article "Ultrafast Dynamics of Polaron Formation" and was included in IOPselect, a special collection of journal articles chosen by the editors based on the criteria of substantial advances or significant breakthroughs, a high degree of novelty, and significant impact on future research.

Dynamics of Localized Photoexcitations in Condensed Matter Systems Susan L. Dexheimer, Washington State University, DMR Broader impact Molecular-based and nanoscale electronic materials have significant potential for the development of new technologies for a wide range of applications. This work contributes to the understanding of key fundamental physical processes that are important for future technological development. Education and outreach activities Four graduate students in physics and materials science have gained research training while working on research supported by this NSF award. The PI teaches classes in optical and materials physics at the undergraduate and graduate levels, and integrates research activities and results into classroom instruction. The PI serves as director of a scholarship program focused on recruiting and retaining women physics students at WSU, and has served on the Graduate Recruiting Committee of the Department of Physics and Astronomy at WSU, contributing to recruitment of under-represented groups. A number of high school student groups from throughout the state of Washington have visited our laser laboratories as part of the outreach activities of the WSU Department of Physics and Astronomy. Professor Susan Dexheimer, NSF Research Experiences for Undergraduates student Nicholas Jackson from Wesleyan University, and WSU physics Ph.D. candidate Jason Mance optimize a femtosecond regenerative amplifier.