In this seminar, I will discuss two unrelated basic physics experiments carried out with soft x-ray pulses at European XFEL:
(A) Magnetic Skyrmions are spin textures which behave as quasi-particles and are characterized by a specific topology. Some types of skyrmions do exist in suitable thin magnetic film systems at room temperature, and they can be generated and efficiently moved around by spin-polarized current pulses. I will discuss how magnetic skyrmions can be generated via laser pulses instead, at unprecedented speed. Building on previous imaging experiments and theoretical simulations of the spin dynamics, the creation mechanism – which necessarily involves a change of local topology – could be clarified in resonant scattering experiments at the European XFEL SCS instrument.
(B) The study and exploitation of non-linear light-matter interactions using x-rays has been one of the scientific visions when free electron x-ray lasers were conceived. Stimulated Raman scattering is a key process in this regard, but it is difficult to unambiguously detect via the radiation emitted. Analyzing the momenta of the atoms involved, we have established photon-recoil imaging as a powerful alternative approach. As demonstrated at the SQS instrument in an experiment on Neon, this method allows for an almost background-free detection of stimulated x-ray Raman scattering, providing access to non-linear processes on the single atom level.
 F. Büttner, B. Pfau, M. Böttcher, M. Schneider, G. Mercurio, C. M. Günther, P. Hessing, C. Klose, A. Wittmann, K. Gerlinger, L. M. Kern, C. Struber, C. V. Schmising, J. Fuchs, D. Engel, A. Churikova, S. Y. Huang, D. Suzuki, I. Lemesh, M. T. Huang, L. Caretta, D. Weder, J. H. Gaida, M. Möller, T. R. Harvey, S. Zayko, K. Bagschik, R. Carley, L. Mercadier, J. Schlappa, A. Yaroslavtsev, L. Le Guyarder, N. Gerasimova, A. Scherz, C. Deiter, R. Gort, D. Hickin, J. Zhu, M. Turcato, D. Lomidze, F. Erdinger, A. Castoldi, S. Maffessanti, M. Porro, A. Samartsev, J. Sinova, C. Ropers, J. H. Mentink, B. Dupe, G. S. D. Beach, and S. Eisebitt, Observation of fluctuation-mediated picosecond nucleation of a topological phase, Nature Materials (2020). https://doi.org/10.1038/s41563-020-00807-1
 U. Eichmann, H. Rottke, S. Meise, J.-E. Rubensson, J. Söderström, M. Agåker, C. Såthe,
M. Meyer, T. M. Baumann, R. Boll, A. De Fanis, P. Grychtol, M. Ilchen, T. Mazza, J. Montano4, V. Music, Y. Ovcharenko, D. E. Rivas, S. Serkez, R. Wagner, S. Eisebitt, Photon-recoil imaging: Expanding the view of nonlinear x-ray physics, Science 369, 1630 (2020)
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Meeting ID: 916 2798 5429
Robert Carley / Gabriella Mulá-Mathews