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Direct mapping of the formation of a persistent spin helix

Abstract

The spin–orbit interaction (SOI) in zincblende semiconductor quantum wells can be set to a symmetry point, in which spin decay is strongly suppressed for a helical spin mode. Signatures of such a persistent spin helix (PSH) have been probed using the transient spin-grating technique, but it has not yet been possible to observe the formation and the helical nature of a PSH. Here we directly map the diffusive evolution of a local spin excitation into a helical spin mode by a time-resolved and spatially resolved magneto-optical Kerr rotation technique. Depending on its in-plane direction, an external magnetic field interacts differently with the spin mode and either highlights its helical nature or destroys the SU(2) symmetry of the SOI and thus decreases the spin lifetime. All relevant SOI parameters are experimentally determined and confirmed with a numerical simulation of spin diffusion in the presence of SOI.

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Figure 1: Direct mapping of the PSH formation.
Figure 2: Helical spin modes and the PSH.
Figure 3: Spin diffusion and SOI characterization.
Figure 4: Dependence of the total magnetic field Btot on k.
Figure 5: Interplay of the PSH with an external magnetic field.
Figure 6: Detuning from the PSH regime.

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Acknowledgements

We would like to acknowledge financial support from the Swiss National Science Foundation through NCCR Nano and NCCR QSIT, as well as valuable discussions with R. Allenspach, K. Ensslin and Y. Chen.

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Contributions

M.P.W. and G.S. designed the experiment, interpreted the data and wrote the manuscript. M.P.W. performed the time-resolved experiment. C.R. and W.W. grew the samples. G.S. performed numerical simulations.

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Correspondence to G. Salis.

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The authors declare no competing financial interests.

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Walser, M., Reichl, C., Wegscheider, W. et al. Direct mapping of the formation of a persistent spin helix. Nature Phys 8, 757–762 (2012). https://doi.org/10.1038/nphys2383

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