Probing ultrafast spin dynamics with optical pump–probe scanning tunnelling microscopy

Abstract

Studies of spin dynamics in low-dimensional systems are important from both fundamental and practical points of view1,2. Spin-polarized scanning tunnelling microscopy allows localized spin dynamics to be characterized and plays important roles in nanoscale science and technology3,4,5. However, nanoscale analysis of the ultrafast dynamics of itinerant magnetism, as well as its localized characteristics, should be pursued to advance further the investigation of quantum dynamics in functional structures of small systems. Here, we demonstrate the optical pump–probe scanning tunnelling microscopy technique, which enables the nanoscale probing of spin dynamics with the temporal resolution corresponding, in principle, to the optical pulse width. Spins are optically oriented using circularly polarized light, and their dynamics are probed by scanning tunnelling microscopy based on the optical pump–probe method. Spin relaxation in a single quantum well with a width of 6 nm was observed with a spatial resolution of 1 nm. In addition to spin relaxation dynamics, spin precession, which provides an estimation of the Landé g factor, was observed successfully.

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Figure 1: OPP-STM used for spin detection.
Figure 2: OPP and OPP-STM measurements.
Figure 3: Temperature dependence of spin dynamics in GaAs.
Figure 4: OPP-STM measurement on quantum wells.
Figure 5: Spin precession measurement by OPP-STM.

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Acknowledgements

Support from Japan Society for the Promotion of Science (Grants-in-Aid for Scientific Research, 22226003) is acknowledged.

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Contributions

S.Y. performed the experiment and data analysis (with H.S.). Y.A., Z.W. and Y.M. assisted with the measurement. R.O. and H.O. worked on sample preparation. E.M. helped to design the TESLA system. O.T. provided technical advice and helped to design the TESLA system. H.S. organized and supervised the project and edited the paper.

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Correspondence to Hidemi Shigekawa.

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The authors declare no competing financial interests.

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Yoshida, S., Aizawa, Y., Wang, Zh. et al. Probing ultrafast spin dynamics with optical pump–probe scanning tunnelling microscopy. Nature Nanotech 9, 588–593 (2014). https://doi.org/10.1038/nnano.2014.125

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