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Type: Article × Subject: Electron diffraction ×

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    Exchange-Striction Driven Ultrafast Nonthermal Lattice Dynamics in NiO
    (College Park, Md. : APS, 2021) Windsor, Y.W.; Zahn, D.; Kamrla, R.; Feldl, J.; Seiler, H.; Chiang, C.-T.; Ramsteiner, M.; Widdra, W.; Ernstorfer, R.; Rettig, L.
    We use femtosecond electron diffraction to study ultrafast lattice dynamics in the highly correlated antiferromagnetic (AFM) semiconductor NiO. Using the scattering vector (Q) dependence of Bragg diffraction, we introduce Q-resolved effective temperatures describing the transient lattice. We identify a nonthermal lattice state with preferential displacement of O compared to Ni ions, which occurs within ∼0.3  ps and persists for 25 ps. We associate this with transient changes to the AFM exchange striction-induced lattice distortion, supported by the observation of a transient Q asymmetry of Friedel pairs. Our observation highlights the role of spin-lattice coupling in routes towards ultrafast control of spin order.
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    Spot profile analysis and lifetime mapping in ultrafast electron diffraction: Lattice excitation of self-organized Ge nanostructures on Si(001)
    (Melville, NY : AIP Publishing LLC, 2015) Frigge, T.; Hafke, B.; Tinnemann, V.; Witte, T.; Horn-von Hoegen, M.
    Ultrafast high energy electron diffraction in reflection geometry is employed to study the structural dynamics of self-organized Germanium hut-, dome-, and relaxed clusters on Si(001) upon femtosecond laser excitation. Utilizing the difference in size and strain state the response of hut- and dome clusters can be distinguished by a transient spot profile analysis. Surface diffraction from {105}-type facets provide exclusive information on hut clusters. A pixel-by-pixel analysis of the dynamics of the entire diffraction pattern gives time constants of 40, 160, and 390 ps, which are assigned to the cooling time constants for hut-, dome-, and relaxed clusters.