Publications by authors named "Sergey Zayko"

4 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

Nanoscale magnetic imaging using circularly polarized high-harmonic radiation.

Sci Adv 2017 12 15;3(12):eaao4641. Epub 2017 Dec 15.

4th Physical Institute, University of Göttingen, Göttingen 37077, Germany.

This work demonstrates nanoscale magnetic imaging using bright circularly polarized high-harmonic radiation. We utilize the magneto-optical contrast of worm-like magnetic domains in a Co/Pd multilayer structure, obtaining quantitative amplitude and phase maps by lensless imaging. A diffraction-limited spatial resolution of 49 nm is achieved with iterative phase reconstruction enhanced by a holographic mask. Harnessing the exceptional coherence of high harmonics, this approach will facilitate quantitative, element-specific, and spatially resolved studies of ultrafast magnetization dynamics, advancing both fundamental and applied aspects of nanoscale magnetism.
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http://dx.doi.org/10.1126/sciadv.aao4641DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5732000PMC
December 2017

Coherent diffractive imaging beyond the projection approximation: waveguiding at extreme ultraviolet wavelengths.

Opt Express 2015 Jul;23(15):19911-21

We study extreme-ultraviolet wave propagation within optically thick nanostructures by means of high-resolution coherent diffractive imaging using high-harmonic radiation. Exit waves from different objects are reconstructed by phase retrieval algorithms, and are shown to be dominated by waveguiding within the sample. The experiments provide a direct visualization of extreme-ultraviolet guided modes, and demonstrate that multiple scattering is a generic feature in extruded nanoscale geometries. The observations are successfully reproduced in numerical and semi-analytical simulations.
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http://dx.doi.org/10.1364/OE.23.019911DOI Listing
July 2015

Toroidal grating astigmatism of high-harmonics characterized by EUV Hartmann sensor.

Opt Express 2015 Jun;23(12):15310-5

The beam transport of single high-order harmonics in a monochromator arrangement is studied. A toroidal grating combines spectral filtering and focusing in order to produce a small individual spot for each harmonic. Here, the effect of small deviations from perfect alignment is investigated. Experimentally, a Hartmann sensor monitors the EUV wavefront while the grating is subjected to an online alignment procedure. The obtained results are confirmed by a simple theoretical description employing optical matrix methods.
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http://dx.doi.org/10.1364/OE.23.015310DOI Listing
June 2015
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