ECE Seminar Series – Dr. Yimei Zhu

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Probing Phonon, Magnon, and Spin Dynamics in 2D Materials Using Advanced Electron Microscopy

Yimei Zhu

Department of Condensed Matter Physics and Materials Science

Brookhaven National Laboratory, Upton, NY 11973 USA

In this presentation, I will highlight our recent advances in the characterization of two-dimensional (2D) materials enabled by state-of-the-art electron microscopy. By integrating atomic-resolution imaging, quantitative diffuse scattering, electron energy-loss spectroscopy, in-situ microscopy, and time-resolved pump–probe ultrafast techniques, we probe structural, electronic, and spin dynamics across multiple length and time scales. Case studies include low-temperature in-situ electric-biasing and magnetic-field experiments that reveal topological spin–chiral texture transitions from stripes containing Bloch lines to nontrivial homochiral skyrmionic bubbles [1], as well as femtosecond laser–induced generation of sub-100 nm skyrmions and electric-field control of their chirality [2]. Ultrafast photoexcitation uncovers the rapid formation of topological defects in a charge-density-wave system [3], while microwave-driven experiments elucidate how spin (anti)vortices and domain walls govern spin-wave emission and propagation [4]. Together, these studies demonstrate the power of advanced electron microscopy to elucidate phonon, magnon, and spin-lattice coupling mechanisms and to reveal emergent phenomena in 2D quantum materials and functional devices.

References
[1] Han, M.-G., et al., “Topological magnetic-spin textures in two-dimensional van der Waals Cr2Ge2Te6”, Nano Lett. 19, 11, 7859-7865 (2019).
[2] Li, Z., et al., “Room-temperature sub-100nm Néel-type skyrmions in non-stoichiometric van der Waals ferromagnet Fe3-xGaTe2 with ultrafast laser writability”, Nat. Comm., 15:1017 (2024).
[3] Cheng, Y., et al., “Ultrafast formation of topological defects in a two-dimensional charge density wave”. Nature Physics, 20, 54–60 (2024).
[4] Liu, C., et al., “Correlated spin-wave generation and domain-wall oscillation in a topologically textured magnetic film”, Nature Materials, 24, 406–413 (2025).