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Nano-to-micro spatiotemporal imaging of magnetic skyrmions life cycle

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 Added by Takahiro Shimojima
 Publication date 2021
  fields Physics
and research's language is English




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Magnetic skyrmions are the self-organized topological spin textures behaving like particles. Because of their fast creation and typically long lifetime, experimental verification of skyrmions creation/annihilation processes has been challenging. Here we successfully track skyrmions dynamics in defect-introduced Co9Zn9Mn2, by using pump-probe Lorentz transmission electron microscope. Following the nanosecond-photothermal excitation, we resolve 160-nm-skyrmions proliferation at <1 ns, contraction at 5 ns, drift from 10 ns to 4 microsecond and coalescence at 5 microsecond. These motions relay the multiscale arrangement and relaxation of skyrmion clusters in a repeatable cycle of 20 kHz. Such repeatable dynamics of skyrmions, arising from the weakened but still persistent topological protection around defects, enables us to visualize the whole life of the skyrmions, as well as demonstrating the possible high-frequency manipulations of topological charges brought by skyrmions.



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Van der Waals materials exhibit naturally passivated surfaces and can form versatile heterostructures, enabling observation of carrier transport mechanisms not seen in three-dimensional materials. Here we report observation of a band bending junction, a new type of semiconductor homojunction whose surface potential landscape depends solely on a difference in thickness between the two semiconductor regions atop a buried heterojunction interface. Using MoS2 on Au to form a buried heterojunction interface, we find that lateral surface potential differences can arise in MoS2 from the local extent of vertical band bending in thin and thick MoS2 regions. Using scanning ultrafast electron microscopy, we examine the spatiotemporal dynamics of photogenerated charge carriers and find that lateral carrier separation is enabled by a band bending junction, which is confirmed with semiconductor transport simulations. Band bending junctions may therefore enable new electronic and optoelectronic devices in Van der Waals materials that rely on thickness variations rather than doping to separate charge carriers.
146 - Y. P. Pan , S. Y. Wang , X. Y. Liu 2019
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