Topological Phase Transitions and Nonlinear Interaction of X-Rays with Matter

by Prof. Stefan Eisebitt (Max-Born-Institute, Berlin)

Tuesday 1 Dec 2020, 13:00 → 14:00 Europe/Berlin

Zoom meeting

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.[1]

(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.[2]

[1] 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

[2] 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)

Join Zoom Meeting
https://xfel.zoom.us/j/91627985429?pwd=N1I0U2IrWDdyYWpjeE03Sk1KNkUvZz09

Meeting ID: 916 2798 5429
Passcode: 777823