Electrical detection of charge-current-induced spin polarization due to spin-momentum locking in Bi2Se3

Abstract

Topological insulators exhibit metallic surface states populated by massless Dirac fermions with spin-momentum locking, where the carrier spin lies in-plane, locked at right angles to the carrier momentum. Here, we show that a charge current produces a net spin polarization via spin-momentum locking in Bi2Se3 films, and this polarization is directly manifested as a voltage on a ferromagnetic contact. This voltage is proportional to the projection of the spin polarization onto the contact magnetization, is determined by the direction and magnitude of the charge current, scales inversely with Bi2Se3 film thickness, and its sign is that expected from spin-momentum locking rather than Rashba effects. Similar data are obtained for two different ferromagnetic contacts, demonstrating that these behaviours are independent of the details of the ferromagnetic contact. These results demonstrate direct electrical access to the topological insulators’ surface-state spin system and enable utilization of its remarkable properties for future technological applications.

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Figure 1: Schematic of TI surface bands and experimental concept.
Figure 2: Schematic of contacts and transport devices.
Figure 3: TI spin polarization detected as a voltage with Fe/Al2O3 contacts.
Figure 4: TI spin polarization detected as a voltage with Fe/Al2O3 and Co/MgO/graphene contacts.
Figure 5: Dependence of the ferromagnetic detector voltage on bias current, thickness and temperature.

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Acknowledgements

The authors acknowledge support for this work from core programmes at the Naval Research Laboratory, and the Office of Naval Research contract N0001413WX21513.

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Contributions

C.H.L., L.L. and B.T.J. conceived and designed the experiments. Y.L. and L.L. grew the Bi2Se3 films. J.T.R. provided the large-area graphene. C.H.L. fabricated the devices and performed the transport measurements with assistance from O.M.J.E. C.H.L., O.M.J.E. and B.T.J. analysed the data. B.T.J. and C.H.L. wrote the paper. All authors discussed the results and commented on the manuscript.

Corresponding authors

Correspondence to C. H. Li or B. T. Jonker.

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Li, C., van ‘t Erve, O., Robinson, J. et al. Electrical detection of charge-current-induced spin polarization due to spin-momentum locking in Bi2Se3. Nature Nanotech 9, 218–224 (2014). https://doi.org/10.1038/nnano.2014.16

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