Pseudospin-driven spin relaxation mechanism in graphene

Abstract

The prospect of transporting spin information over long distances in graphene, possible because of its small intrinsic spin–orbit coupling (SOC) and vanishing hyperfine interaction, has stimulated intense research exploring spintronics applications. However, measured spin relaxation times are orders of magnitude smaller than initially predicted, while the main physical process for spin dephasing and its charge-density and disorder dependences remain unconvincingly described by conventional mechanisms. Here, we unravel a spin relaxation mechanism for non-magnetic samples that follows from an entanglement between spin and pseudospin driven by random SOC, unique to graphene. The mixing between spin and pseudospin-related Berry’s phases results in fast spin dephasing even when approaching the ballistic limit, with increasing relaxation times away from the Dirac point, as observed experimentally. The SOC can be caused by adatoms, ripples or even the substrate, suggesting novel spin manipulation strategies based on the pseudospin degree of freedom.

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Figure 1: Spin dynamics in disordered graphene.
Figure 2: Spin relaxation times and transport mechanisms.
Figure 3: Spin relaxation times deduced from the continuum and microscopic models.
Figure 4: Spin and pseudospin dynamics in graphene with ρ = 8% of adatoms.

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Acknowledgements

We thank A. Cummings for a critical reading of the manuscript. The research leading to these results has received funding from the European Union Seventh Framework Programme under grant agreement number 604391 Graphene Flagship. This work was also funded by Spanish Ministry of Economy and Competitiveness under contracts MAT2012-33911 and MAT2010-18065. S.O.V. acknowledges ERC Grant agreement 308023 SPINBOUND.

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D.V.T., D.S. and F.O. designed the models and performed the calculations. D.V.T., F.O., S.O.V. and S.R. carried out analyses and interpretation. F.O., S.O.V. and S.R. wrote the text and all authors contributed to the manuscript and Supplementary Information.

Corresponding author

Correspondence to Stephan Roche.

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The authors declare no competing financial interests.

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Tuan, D., Ortmann, F., Soriano, D. et al. Pseudospin-driven spin relaxation mechanism in graphene. Nature Phys 10, 857–863 (2014). https://doi.org/10.1038/nphys3083

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