Berlin 2018 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 22: Superconductivity: Topological Defects in Superconductors and Magnets (joint session TT/MA)
TT 22.4: Vortrag
Montag, 12. März 2018, 15:45–16:00, HFT-FT 101
Skyrmion optical creation/annihilation in a chiral magnet — •Gabriele Berruto1, Ivan Madan1, Yoshie Murooka1, Giovanni Maria Vanacore1, Enrico Pomarico1, Damien McGrouther2, Yoshihiko Togawa2, Heinrik Rønnow1, and Fabrizio Carbone1 — 1Institute of Physics, EPFL, Lausanne, Switzerland — 2SUPA, University of Glasgow, United Kingdom
We show that single light pulses of different duration and color can create and annihilate skyrmions for a broad range of parameters in the magnetic phase diagram of a 50 nm-thick slab of FeGe, a prototypical chiral magnet. Using a combination of camera-rate and ns pump-probe cryo-Lorentz Transmission Electron Microscopy, we directly resolve the spatio-temporal evolution of the magnetization ensuing (fs and ns) optical excitation. When we excite optically the skyrmion lattice, its structural parameters are not modified, only the magnetization being affected: it transiently decreases, and recovers to the initial value over long (μs) time scales, reflecting the important role of the cooling rate of the system. Contrary to previously reported cases in different systems, in our experiment the skyrmions are not created via a transient demagnetized (paramagnetic) state. The laser pulses transiently heat the system, driving it into a region of the phase diagram where the appearance of skyrmions is strongly favored, but still staying far below the Curie temperature. The system then supercools down to base temperature, and skyrmions remain frozen into their (meta)stable state. The skyrmion topological charge is injected from geometric edges, defects, and magnetic boundaries.