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  • Letter
  • Open Access

Ultrafast optical generation of antiferromagnetic meron-antimeron pairs with conservation of topological charge

Sumit Ghosh, Stefan Blügel, and Yuriy Mokrousov
Phys. Rev. Research 5, L022007 – Published 7 April 2023
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  • INTRODUCTION
  • MODEL AND METHOD
  • RESULT AND DISCUSSION
  • CONCLUSIONS
  • ACKNOWLEDGMENTS
    • References

    Abstract

    We propose a new mechanism to produce a meron-antimeron pair in a two dimensional antiferromagnet with an ultrafast laser pulse via a thermal Schwinger mechanism. Unlike ultrafast skyrmion nucleation, this process conserves total topological charge. We systematically show different stages of the dynamics and define proper topological invariants to characterize the configurations. The emergent structure can retain its topological structure for up to 100 ps. By introducing a topological structure factor we show that pair formation is robust against any random choice of initial magnetic configuration and can survive against disorder. Our findings demonstrate that the rich world of spin textures, which goes beyond conventional skyrmions, can be reached optically.

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    • Received 8 December 2022
    • Revised 21 February 2023
    • Accepted 17 March 2023

    DOI:https://doi.org/10.1103/PhysRevResearch.5.L022007

    Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

    Published by the American Physical Society

    Physics Subject Headings (PhySH)

    1. Research Areas
    Magnetic textureUltrafast magnetic effects
    Condensed Matter, Materials & Applied Physics

    Authors & Affiliations

    Sumit Ghosh1,2,*, Stefan Blügel1, and Yuriy Mokrousov1,2

    • 1Peter Grünberg Institut (PGI-1), Forschungszentrum Jülich GmbH, 52428 Jülich, Germany
    • 2Institute of Physics, Johannes Gutenberg-University Mainz, 55128 Mainz, Germany

    • *s.ghosh@fz-juelich.de

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    Issue

    Vol. 5, Iss. 2 — April - June 2023

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    • Figure 1
      Figure 1

      Generation of a meron-antimeron pair by an ultrafast laser pulse. (a) Initial antiferromagnetic configuration. Yellow line denotes the circularly polarized laser. (b) Emergence of a quasistable meron-antimeron pair after the action of the laser pulse. The blue and red regions show the negative and positive topological charge.

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    • Figure 2
      Figure 2

      Time evolution of different physical observables. (a) Change of occupation for different states with their color denoting corresponding eigenvalues. Here we show every 5th state. Gray shaded region shows the time delay between the incident of laser and onset of magnetization dynamics. (b) Change of magnetization vector (solid) and effective field (dashed) components of the magnetic moment at x=1,y=10. Yellow line denotes the x component of the laser electric field. (c) Change of average total energy (gray dashed) and rate of change of energy (red) where the green portion shows when the system absorbs energy. (d) Evolution of different components of average torque.

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    • Figure 3
      Figure 3

      Skyrmionic charge and winding number for antiferromagnetic meron-antimeron pairs. (a) Distribution of skyrmionic charge is shown with red and blue color denoting positive and negative values, with winding centers W1,2,3,4 marked with yellow spheres. Solid blue and red lines show the contours along which winding number is calculated with red and blue colors denoting a winding number ±1. (b) Time evolution of total absolute skyrmion charge density and winding number.

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    • Figure 4
      Figure 4

      Topological structure factor and its stability. (a) Topological structure factor of the configuration shown in Fig. 3. Inset shows the corresponding real space distribution of the topological charge. (b) Average topological structure factor averaged over 70 different configurations. (c) Average topological structure factor for different strengths of scalar impurity averaged over 32 different configurations and scaled with its average value at V0=0. For each configuration we consider the mean value at q=0.1(±x̂±ŷ)π.

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