Picosecond Ultrasonics in Magnetic Topological Insulator MnBi₂Te₂
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Fonseca, Jordan, Geoffrey M. Diederich, Dmitry Ovchinnikov, Jiaqiang Yan, Di Xiao, and Xiaodong Xu. “Picosecond Ultrasonics in Magnetic Topological Insulator MnBi₂Te₂.” Nano Letters 24, no. 34 (2024): 10562–68. https://doi.org/10.1021/acs.nanolett.4c01287.
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This document is the Accepted Manuscript version of a Published Work that appeared in final form in Nano Letters, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://doi.org/10.1021/acs.nanolett.4c01287.
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MnBi₂Te₂ is a magnetic topological insulator with layered A-type antiferromagnetic order. It exhibits a rich layer- and magnetic-state dependent topological phase diagram; however, much about the coupling between spin, charge, and lattice remains to be explored. In this work, we report that MnBi₂Te₂ is an excellent acoustic phonon cavity by realizing phonon frequency combs using picosecond ultrasonics. With the generated acoustic phonon wavepackets, we demonstrate that the timing and phase of acoustic echoes can be used to detect the presence of stacking faults between van der Waals layers buried deep within the crystal. Furthermore, by implementing this nondestructive ultrafast optical measurement in conjunction with time-resolved magneto-optical Kerr effect experiments, we uncover that out-of-plane vibrations in MnBi₂Te₂ do not couple to the magnetic order, i.e. there is no appreciable magnetostriction. Our work points out how a well-developed technique can probe the structural defects and phonon pulse engineering in layered topological insulators.