Publications by authors named "Justine Schlappa"

3 Publications

  • Page 1 of 1

Observation of fluctuation-mediated picosecond nucleation of a topological phase.

Nat Mater 2021 Jan 5;20(1):30-37. Epub 2020 Oct 5.

European XFEL, Schenefeld, Germany.

Topological states of matter exhibit fascinating physics combined with an intrinsic stability. A key challenge is the fast creation of topological phases, which requires massive reorientation of charge or spin degrees of freedom. Here we report the picosecond emergence of an extended topological phase that comprises many magnetic skyrmions. The nucleation of this phase, followed in real time via single-shot soft X-ray scattering after infrared laser excitation, is mediated by a transient topological fluctuation state. This state is enabled by the presence of a time-reversal symmetry-breaking perpendicular magnetic field and exists for less than 300 ps. Atomistic simulations indicate that the fluctuation state largely reduces the topological energy barrier and thereby enables the observed rapid and homogeneous nucleation of the skyrmion phase. These observations provide fundamental insights into the nature of topological phase transitions, and suggest a path towards ultrafast topological switching in a wide variety of materials through intermediate fluctuating states.
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http://dx.doi.org/10.1038/s41563-020-00807-1DOI Listing
January 2021

Femtosecond X-ray induced changes of the electronic and magnetic response of solids from electron redistribution.

Nat Commun 2019 11 21;10(1):5289. Epub 2019 Nov 21.

SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, CA, 94025, USA.

Resonant X-ray absorption, where an X-ray photon excites a core electron into an unoccupied valence state, is an essential process in many standard X-ray spectroscopies. With increasing X-ray intensity, the X-ray absorption strength is expected to become nonlinear. Here, we report the onset of such a nonlinearity in the resonant X-ray absorption of magnetic Co/Pd multilayers near the Co L[Formula: see text] edge. The nonlinearity is directly observed through the change of the absorption spectrum, which is modified in less than 40 fs within 2 eV of its threshold. This is interpreted as a redistribution of valence electrons near the Fermi level. For our magnetic sample this also involves mixing of majority and minority spins, due to sample demagnetization. Our findings reveal that nonlinear X-ray responses of materials may already occur at relatively low intensities, where the macroscopic sample is not destroyed, providing insight into ultrafast charge and spin dynamics.
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http://dx.doi.org/10.1038/s41467-019-13272-5DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6872582PMC
November 2019

Transition-Metal Nanoparticle Oxidation in a Chemically Nonhomogenous Environment Revealed by 2p3d Resonant X-ray Emission.

J Phys Chem Lett 2013 Apr 25;4(7):1161-6. Epub 2013 Mar 25.

‡Paul Scherrer Institut (PSI), Swiss Light Source, CH-5232 Villigen, Switzerland.

X-ray absorption spectroscopy (XAS) is often employed in fields such as catalysis to determine whether transition-metal nanoparticles are oxidized. Here we show 2p3/2 XAS and 2p3d resonant X-ray emission spectroscopy (RXES) data of oleate-coated cobalt nanoparticles with average diameters of 4.0, 4.2, 5.0, 8.4, and 15.2 nm. Two particle batches were exposed to air for different periods of time, whereas the others were measured as synthesized. In the colloidal nanoparticles, the cobalt sites can have different chemical environments (metallic/oxidized/surface-coordinated), and it is shown that most XAS data cannot distinguish whether the nanoparticles are oxidized or surface-coated. In contrast, the high-energy resolution RXES spectra reveal whether more than the first metal layer is oxidized based on the unique energetic separation of spectral features related to the formal metal (X-ray fluorescence) or to a metal oxide (d-d excitations). This is the first demonstration of metal 2p3d RXES as a novel surface science tool.
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http://dx.doi.org/10.1021/jz4002696DOI Listing
April 2013
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